APPARATUS FOR HUMIDIFYING A RESPIRATORY GAS

Abstract

An apparatus is provided to change the absolute humidity of a flow of air for delivery to an entrance of the airways of a patient, the change being compared to the absolute humidity of ambient air. The apparatus has a reservoir configured to hold a volume of liquid. A heating element creates vapour from the liquid. A chamber is provided to mix the flow of air with the vapour. The apparatus has a body having a first wall structure with a chamber inlet port. A closure element having an air inlet port for pneumatically connecting to a source of the flow of air is secured to the body to provide a sealed gas flow path between the air inlet port and the chamber inlet port, and a liquid trap in the gas flow path.

Claims

1. An apparatus to change the absolute humidity of a flow of air for delivery to an entrance of the airways of a patient, the change being compared to the absolute humidity of ambient air, the apparatus comprising: a reservoir configured to hold a volume of liquid; a heating element to create vapour from the liquid; a chamber to mix the flow of air with the vapour; a body, the body comprising a first wall structure, the first wall structure comprising an upright body wall, wherein the upright body wall is in a substantially upright orientation when the apparatus is in an intended working orientation, the upright body wall comprising a chamber inlet port; a closure element comprising an air inlet port for pneumatically connecting to a source of the flow of air; wherein the closure element is secured to the body to provide a sealed gas flow path between the air inlet port and the chamber inlet port, and a liquid trap in the gas flow path, wherein the upright body wall forms part of the sealed gas flow path.

2. The apparatus of claim 1, wherein the first wall structure comprises a chamber inlet port sealing portion surrounding the chamber inlet port and extending towards the closure element.

3. The apparatus of claim 2, wherein the chamber inlet port sealing portion comprises a first peripheral wall.

4. The apparatus of claim 1, wherein the closure element comprises an air inlet port sealing portion surrounding the air inlet port and extending towards the first wall structure.

5-9. (canceled)

10. The apparatus of claim 2, comprising a resilient seal, wherein the closure element comprises an air inlet port sealing portion surrounding the air inlet port and extending towards the first wall structure, and wherein the resilient seal comprises a liquid trap portion positioned between the chamber inlet port sealing portion and the air inlet port sealing portion.

11. (canceled)

12. The apparatus of claim 2, comprising a resilient seal, wherein the closure element comprises an air inlet port sealing portion surrounding the air inlet port and extending towards the first wall structure, and wherein the resilient seal comprises a liquid trap portion provided on a rim of the air inlet port sealing portion and configured to seal against the chamber inlet port sealing portion.

13-23. (canceled)

24. The apparatus of claim 1, wherein the first wall structure and the closure element are generally upright when the apparatus is in the intended working orientation.

25. The apparatus of claim 1, wherein when the apparatus is in an intended working orientation, a lowest point of the chamber inlet port is one or more of: inferior to a lowest point of the air inlet port, and superior to an intended liquid fill level of the chamber.

26. (canceled)

27. The apparatus of claim 1 to 26, wherein a centre of the chamber inlet port is at least one of: laterally offset from a centre of the air inlet port, and inferior to a centre of the air inlet port.

28. (canceled)

29. The apparatus of claim 1, wherein the liquid trap is configured to trap a volume of liquid of one of: between about 5 ml to about 100 ml, between about 10 ml to about 80 ml, between about 30 ml to about 80 ml, and about 60 ml.

30-32. (canceled)

33. The apparatus of claim 1, wherein the liquid trap comprises a superior portion provided above the chamber.

34. The apparatus of claim 33, wherein the superior portion of the liquid trap is configured such that liquid drains from the superior portion into an inferior portion of the liquid trap.

35. (canceled)

36. The apparatus of claim 1, wherein the liquid trap comprises a lateral portion.

37. The apparatus of claim 36, wherein a height of the lateral portion is less than a greatest height of the liquid trap.

38. The apparatus of claim 36 , wherein the lateral portion of the liquid trap is configured such that liquid drains from the lateral portion into an inferior portion of the liquid trap.

39. (canceled)

40. The apparatus of claim 1, comprising an inverted receptacle provided to a superior portion of the chamber inlet port when the apparatus is in an intended working orientation.

41. The apparatus of claim 40, wherein the inverted receptacle extends from the body towards the closure element.

42-46. (canceled)

47. The apparatus of claim 1, comprising an interior trap wall extending from the closure element towards the chamber inlet port and surrounding the air inlet port.

48-50. (canceled)

51. The apparatus of claim 1, comprising a baffle portion positioned between the air inlet port and the chamber inlet port.

52. The apparatus of claim 51, wherein the baffle portion is configured to direct liquid flowing from the chamber inlet port in a radial direction.

53-58. (canceled)

59. The apparatus of claim 1, comprising at least one liquid trap partition providing a plurality of liquid trap catchments within the liquid trap.

60. The apparatus of claim 59, wherein the liquid trap comprises a first liquid trap catchment inferior to the chamber inlet port, and a second liquid trap catchment inferior to the first liquid trap catchment when the apparatus is in an inverted from intended working orientation.

61-63. (canceled)

64. The apparatus of claim 60,wherein the at least one liquid trap partition comprises one or more of: an upright intermediary wall and a partition wall extending from the upright intermediary wall towards the body, wherein a superior gap is provided between the chamber inlet port and the partition wall and the superior gap opens into the first liquid trap catchment; and an interior trap wall extending from the closure element towards the chamber inlet port and surrounding the air inlet port to define a third liquid trap catchment around the interior trap wall.

65-68. (canceled)

69. The apparatus of claim 1, wherein the closure element is configured to interact with a secondary closure element to provide the liquid trap.

70. The apparatus of claim 69, wherein the secondary closure element comprises at least the air inlet port for pneumatically connecting to a source of the flow of air.

71. The apparatus of claim 69 , wherein the secondary closure element is one or more of: a component of a device configured to provide the source of the flow of air; a component of a Positive Airway Pressure generator configured to be connected to the apparatus; and configured to act as an interface between the apparatus and a device configured to provide the source of the flow of air.

72-73. (canceled)

74. A respiratory treatment apparatus comprising: a source of a flow of air at positive pressure to ambient; a body constructed and arranged to be fixed in location in use relative to the source; an inlet pneumatic connection structure for connecting to the source to receive sealably the flow of air at positive pressure from the source in use; a container to hold a body of water in use, the container being configured to direct the flow of air so that the flow of air contacts a surface of the body of water in use so that water vapour may transfer from the body of water to the flow of air in use to increase the absolute humidity of the flow of air, the container including a wall constructed at least in part from a material having a relatively high thermal conductivity; a heating element; a temperature sensor; a controller to control the heating element; and an outlet pneumatic connection structure to receive the flow of air with increased absolute humidity; wherein the body is configured to hold the container in location close relative to the heating element so that heat energy may transfer from the heating element to the body of water to increase the absolute humidity of the flow of air, wherein the controller is constructed and arranged to energise the heating element to heat the water without boiling the water, wherein the respiratory treatment apparatus includes a sealing arrangement so that in use the flow of air with increased absolute humidity received at the outlet pneumatic connection structure has a positive pressure with respect to ambient, wherein the inlet pneumatic connection structure comprises an air inlet port, wherein the respiratory treatment apparatus comprises a closure element comprising the air inlet port, wherein the container comprises an upright wall, wherein the upright wall is in a substantially upright orientation when the apparatus is in an intended working orientation, the upright wall comprising a container inlet port, wherein the closure element is secured to the body to provide a sealed gas flow path between the air inlet port and the container inlet port, and a liquid trap in the gas flow path, wherein the upright wall forms part of the sealed gas flow path.

75-76. (canceled)

77. A device for treating a respiratory disorder comprising: a Positive Airway Pressure generator; and an apparatus to change the absolute humidity of a flow of air produced by the Positive Airway Pressure generator for delivery to an entrance of the airways of a patient, wherein the apparatus is configured as claimed in claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0180] The present technology is illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings, in which like reference numerals refer to similar elements including:

4.1 Respiratory Therapy Systems

[0181] FIG. 1A shows a system including a patient 1000 wearing a patient interface 3000, in the form of nasal pillows, receiving a supply of air at positive pressure from an RPT device 4000. Air from the RPT device 4000 is conditioned in a humidifier 5000, and passes along an air circuit 4170 to the patient 1000. A bed partner 1100 is also shown. The patient is sleeping in a supine sleeping position.

[0182] FIG. 1B shows a system including a patient 1000 wearing a patient interface 3000, in the form of a nasal mask, receiving a supply of air at positive pressure from an RPT device 4000. Air from the RPT device is humidified in a humidifier 5000, and passes along an air circuit 4170 to the patient 1000.

[0183] FIG. 1C shows a system including a patient 1000 wearing a patient interface 3000, in the form of a full-face mask, receiving a supply of air at positive pressure from an RPT device 4000. Air from the RPT device is humidified in a humidifier 5000, and passes along an air circuit 4170 to the patient 1000. The patient is sleeping in a side sleeping position.

4.2 Respiratory System and Facial Anatomy

[0184] FIG. 2A shows an overview of a human respiratory system including the nasal and oral cavities, the larynx, vocal folds, oesophagus, trachea, bronchus, lung, alveolar sacs, heart and diaphragm.

[0185] FIG. 2B shows a view of a human upper airway including the nasal cavity, nasal bone, lateral nasal cartilage, greater alar cartilage, nostril, lip superior, lip inferior, larynx, hard palate, soft palate, oropharynx, tongue, epiglottis, vocal folds, oesophagus and trachea.

4.3 Patient Interface

[0186] FIG. 3A shows a patient interface in the form of a nasal mask in accordance with one form of the present technology.

[0187] FIG. 3B shows a patient interface in the form of a nasal cannula in accordance with one form of the present technology.

4.4 Rpt Device

[0188] FIG. 4A shows an RPT device in accordance with one form of the present technology.

[0189] FIG. 4B is a schematic diagram of the pneumatic path of an RPT device in accordance with one form of the present technology. The directions of upstream and downstream are indicated with reference to the blower and the patient interface. The blower is defined to be upstream of the patient interface and the patient interface is defined to be downstream of the blower, regardless of the actual flow direction at any particular moment. Items which are located within the pneumatic path between the blower and the patient interface are downstream of the blower and upstream of the patient interface.

[0190] FIG. 4C is a schematic diagram of the electrical components of an RPT device in accordance with one form of the present technology.

[0191] FIG. 4D is a schematic diagram of the algorithms implemented in an RPT device in accordance with one form of the present technology.

[0192] FIG. 4E is a flow chart illustrating a method carried out by the therapy engine module of FIG. 4D in accordance with one form of the present technology.

4.5 Humidifier

[0193] FIG. 5A shows an isometric view of a humidifier in accordance with one form of the present technology.

[0194] FIG. 5B shows an isometric view of a humidifier in accordance with one form of the present technology, showing a humidifier reservoir 5110 removed from the humidifier reservoir dock 5130.

[0195] FIG. 5C shows a schematic of a humidifier in accordance with one form of the present technology.

[0196] FIG. 5D shows an RPT device in accordance with one form of the present technology.

[0197] FIG. 5E shows the RPT device of FIG. 5D connected to a releasable component in the form of a humidifier.

[0198] FIG. 5F shows the respiratory therapy device and humidifier of FIG. 5E with the lid of the humidifier in an open position.

[0199] FIG. 5G shows a cross-section through a housing for a humidifier having a liquid trap in accordance with one form of the present technology.

[0200] FIG. 5H shows a schematic of a humidifier having a liquid trap in accordance with one form of the present technology.

[0201] FIG. 5I shows an end view of a humidifier having a liquid trap in accordance with one form of the present technology.

[0202] FIG. 5J shows a cross-section through a humidifier housing having a liquid trap in in accordance with one form of the present technology, showing the humidifier in a tipped orientation.

[0203] FIG. 5K shows a cross-section through a humidifier housing having a liquid trap in in accordance with one form of the present technology, showing the humidifier in a level condition.

[0204] FIG. 5L shows a cross-section through a humidifier housing having a liquid trap in in accordance with one form of the present technology.

[0205] FIG. 5M shows an end view of an end cap of a humidifier housing in accordance with one form of the present technology.

[0206] FIG. 6A shows a perspective view of an inverted receptacle for use in a humidifier having a liquid trap in accordance with one form of the present technology.

[0207] FIG. 6B shows a cross-section through a humidifier housing having a liquid trap comprising an inverted receptacle in accordance with one form of the present technology.

[0208] FIG. 6C shows a cross-section through a receptacle for use in a humidifier having a liquid trap in accordance with one form of the present technology.

[0209] FIG. 6D shows a cross-section through a humidifier housing having a liquid trap comprising an inverted receptacle in accordance with one form of the present technology.

[0210] FIG. 7A shows a cross-section through a humidifier housing having a liquid trap in in accordance with one form of the present technology, showing the humidifier in a level orientation.

[0211] FIG. 7B shows a cross-section through a humidifier housing having a liquid trap in in accordance with one form of the present technology, showing the humidifier in an upended condition.

[0212] FIG. 7C shows a cross-section through a humidifier housing having a liquid trap in in accordance with one form of the present technology.

[0213] FIG. 8A shows a perspective view of a receptacle comprising a baffle portion for use in a humidifier having a liquid trap in accordance with one form of the present technology.

[0214] FIG. 8B shows a perspective view of the receptacle relative to an air inlet port of a humidifier in accordance with one form of the present technology

[0215] FIG. 8C shows a perspective view of a receptacle comprising a baffle portion for use in a humidifier having a liquid trap in accordance with one form of the present technology.

[0216] FIG. 8D shows a perspective view of a baffle portion for use in a humidifier having a liquid trap in accordance with one form of the present technology.

[0217] FIG. 9 shows a cross-section through a humidifier housing having a liquid trap comprising a liquid trap partition in accordance with one form of the present technology.

[0218] FIG. 10 is a front view of a moveable barrier for use in a humidifier having a liquid trap in accordance with one form of the present technology.

[0219] FIG. 11 shows a cross-section through a humidifier housing having a liquid trap comprising a secondary closure element in accordance with one form of the present technology.

DETAILED DESCRIPTION OF EXAMPLES OF THE TECHNOLOGY

[0220] Before the present technology is described in further detail, it is to be understood that the technology is not limited to the particular examples described herein, which may vary. It is also to be understood that the terminology used in this disclosure is for the purpose of describing only the particular examples discussed herein, and is not intended to be limiting.

[0221] The following description is provided in relation to various examples which may share one or more common characteristics and/or features. It is to be understood that one or more features of any one example may be combinable with one or more features of another example or other examples. In addition, any single feature or combination of features in any of the examples may constitute a further example.

5.1 Therapy

[0222] In one form, the present technology comprises a method for treating a respiratory disorder comprising applying positive pressure to the entrance of the airways of a patient 1000.

[0223] In certain examples of the present technology, a supply of air at positive pressure is provided to the nasal passages of the patient via one or both nares.

[0224] In certain examples of the present technology, mouth breathing is limited, restricted or prevented.

5.2 Respiratory Therapy Systems

[0225] In one form, the present technology comprises a respiratory therapy system for treating a respiratory disorder. The respiratory therapy system may comprise an RPT device 4000 for supplying a flow of air to the patient 1000 via an air circuit 4170 and a patient interface 3000 or 3800.

5.3 Patient Interface

[0226] A non-invasive patient interface 3000 in accordance with one aspect of the present technology comprises the following functional aspects: a seal-forming structure 3100, a plenum chamber 3200, a positioning and stabilising structure 3300, a vent 3400, one form of connection port 3600 for connection to air circuit 4170, and a forehead support 3700. In some forms a functional aspect may be provided by one or more physical components. In some forms, one physical component may provide one or more functional aspects. In use the seal-forming structure 3100 is arranged to surround an entrance to the airways of the patient so as to maintain positive pressure at the entrance(s) to the airways of the patient 1000. The sealed patient interface 3000 is therefore suitable for delivery of positive pressure therapy.

[0227] An unsealed patient interface 3800, in the form of a nasal cannula, includes nasal prongs 3810a, 3810b which can deliver air to respective nares of the patient 1000 via respective orifices in their tips. Such nasal prongs do not generally form a seal with the inner or outer skin surface of the nares. The air to the nasal prongs may be delivered by one or more air supply lumens 3820a, 3820b that are coupled with the nasal cannula 3800. The lumens 3820a, 3820b lead from the nasal cannula 3800 to a respiratory therapy device via an air circuit. The unsealed patient interface 3800 is particularly suitable for delivery of flow therapies, in which the RPT device generates the flow of air at controlled flow rates rather than controlled pressures. The “vent” at the unsealed patient interface 3800, through which excess airflow escapes to ambient, is the passage between the end of the prongs 3810a and 3810b of the cannula 3800 via the patient’s nares to atmosphere.

[0228] If a patient interface is unable to comfortably deliver a minimum level of positive pressure to the airways, the patient interface may be unsuitable for respiratory pressure therapy.

[0229] The patient interface 3000 in accordance with one form of the present technology is constructed and arranged to be able to provide a supply of air at a positive pressure of at least 6 cmH.sub.2O with respect to ambient.

[0230] The patient interface 3000 in accordance with one form of the present technology is constructed and arranged to be able to provide a supply of air at a positive pressure of at least 10 cmH.sub.2O with respect to ambient.

[0231] The patient interface 3000 in accordance with one form of the present technology is constructed and arranged to be able to provide a supply of air at a positive pressure of at least 20 cmH.sub.2O with respect to ambient.

5.4 RPT Device

[0232] An RPT device 4000 in accordance with one aspect of the present technology comprises mechanical, pneumatic, and/or electrical components and is configured to execute one or more algorithms 4300, such as any of the methods, in whole or in part, described herein. The RPT device 4000 may be configured to generate a flow of air for delivery to a patient’s airways, such as to treat one or more of the respiratory conditions described elsewhere in the present document.

[0233] In one form, the RPT device 4000 is constructed and arranged to be capable of delivering a flow of air in a range of -20 L/min to +150 L/min while maintaining a positive pressure of at least 6 cmH.sub.2O, or at least 10 cmH.sub.2O, or at least 20 cmH.sub.2O.

[0234] The RPT device may have an external housing 4010, formed in two parts, an upper portion 4012 and a lower portion 4014. Furthermore, the external housing 4010 may include one or more panel(s) 4015. The RPT device 4000 comprises a chassis 4016 that supports one or more internal components of the RPT device 4000. The RPT device 4000 may include a handle 4018.

[0235] The pneumatic path of the RPT device 4000 may comprise one or more air path items, e.g., an inlet air filter 4112, an inlet muffler 4122, a pressure generator 4140 capable of supplying air at positive pressure (e.g., a blower 4142), an outlet muffler 4124 and one or more transducers 4270, such as pressure sensors 4272 and flow rate sensors 4274.

[0236] One or more of the air path items may be located within a removable unitary structure which will be referred to as a pneumatic block 4020. The pneumatic block 4020 may be located within the external housing 4010. In one form a pneumatic block 4020 is supported by, or formed as part of, the chassis 4016.

[0237] The RPT device 4000 may have an electrical power supply 4210, one or more input devices 4220, a central controller 4230, a therapy device controller 4240, a pressure generator 4140, one or more protection circuits 4250, memory 4260, transducers 4270, data communication interface 4280 and one or more output devices 4290. Electrical components 4200 may be mounted on a single Printed Circuit Board Assembly (PCBA) 4202. In an alternative form, the RPT device 4000 may include more than one PCBA 4202.

5.4.1 RPT Device Mechanical & Pneumatic Components

[0238] An RPT device may comprise one or more of the following components in an integral unit. In an alternative form, one or more of the following components may be located as respective separate units.

5.4.1.1 Air Filter(s)

[0239] An RPT device in accordance with one form of the present technology may include an air filter 4110, or a plurality of air filters 4110.

[0240] In one form, an inlet air filter 4112 is located at the beginning of the pneumatic path upstream of a pressure generator 4140.

[0241] In one form, an outlet air filter 4114, for example an antibacterial filter, is located between an outlet of the pneumatic block 4020 and a patient interface 3000 or 3800.

5.4.1.2 Muffler(s)

[0242] An RPT device in accordance with one form of the present technology may include a muffler 4120, or a plurality of mufflers 4120.

[0243] In one form of the present technology, an inlet muffler 4122 is located in the pneumatic path upstream of a pressure generator 4140.

[0244] In one form of the present technology, an outlet muffler 4124 is located in the pneumatic path between the pressure generator 4140 and a patient interface 3000 or 3800.

5.4.1.3 Pressure Generator

[0245] In one form of the present technology, a pressure generator 4140 for producing a flow, or a supply, of air at positive pressure is a controllable blower 4142. For example, the blower 4142 may include a brushless DC motor 4144 with one or more impellers. The impellers may be located in a volute. The blower may be capable of delivering a supply of air, for example at a rate of up to about 120 litres/minute, at a positive pressure in a range from about 4 cmH.sub.2O to about 20 cmH.sub.2O, or in other forms up to about 30 cmH.sub.2O when delivering respiratory pressure therapy. The blower may be as described in any one of the following patents or patent applications the contents of which are incorporated herein by reference in their entirety: U.S. Pat. No. 7,866,944; U.S. Pat. No. 8,638,014; U.S. Pat. No. 8,636,479; and PCT Pat. Application Publication No. WO 2013/020167.

[0246] The pressure generator 4140 is under the control of the therapy device controller 4240.

[0247] In other forms, a pressure generator 4140 may be a piston-driven pump, a pressure regulator connected to a high pressure source (e.g. compressed air reservoir), or a bellows.

5.4.1.4 Transducer(s)

[0248] Transducers may be internal of the RPT device, or external of the RPT device. External transducers may be located for example on or form part of the air circuit, e.g., the patient interface. External transducers may be in the form of noncontact sensors such as a Doppler radar movement sensor that transmit or transfer data to the RPT device.

[0249] In one form of the present technology, one or more transducers 4270 are located upstream and/or downstream of the pressure generator 4140. The one or more transducers 4270 may be constructed and arranged to generate signals representing properties of the flow of air such as a flow rate, a pressure or a temperature at that point in the pneumatic path.

[0250] In one form of the present technology, one or more transducers 4270 may be located proximate to the patient interface 3000 or 3800.

[0251] In one form, a signal from a transducer 4270 may be filtered, such as by low-pass, high-pass or band-pass filtering.

5.4.1.4.1 Flow Rate Sensor

[0252] A flow rate sensor 4274 in accordance with the present technology may be based on a differential pressure transducer, for example, an SDP600 Series differential pressure transducer from SENSIRION.

[0253] In one form, a signal generated by the flow rate sensor 4274 and representing a flow rate is received by the central controller 4230.

5.4.1.4.2 Pressure Sensor

[0254] A pressure sensor 4272 in accordance with the present technology is located in fluid communication with the pneumatic path. An example of a suitable pressure sensor is a transducer from the HONEYWELL ASDX series. An alternative suitable pressure sensor is a transducer from the NPA Series from GENERAL ELECTRIC.

[0255] In one form, a signal generated by the pressure sensor 4272 is received by the central controller 4230.

5.4.1.4.3 Motor Speed Transducer

[0256] In one form of the present technology a motor speed transducer 4276 is used to determine a rotational velocity of the motor 4144 and/or the blower 4142. A motor speed signal from the motor speed transducer 4276 may be provided to the therapy device controller 4240. The motor speed transducer 4276 may, for example, be a speed sensor, such as a Hall effect sensor.

5.4.1.5 Anti-Spill Back Valve

[0257] In one form of the present technology, an anti-spill back valve 4160 is located between the humidifier 5000 and the pneumatic block 4020. The anti-spill back valve is constructed and arranged to reduce the risk that water will flow upstream from the humidifier 5000, for example to the motor 4144.

5.4.2 RPT Device Electrical Components

5.4.2.1 Power Supply

[0258] A power supply 4210 may be located internal or external of the external housing 4010 of the RPT device 4000.

[0259] In one form of the present technology, power supply 4210 provides electrical power to the RPT device 4000 only. In another form of the present technology, power supply 4210 provides electrical power to both RPT device 4000 and humidifier 5000.

5.4.2.2 Input Devices

[0260] In one form of the present technology, an RPT device 4000 includes one or more input devices 4220 in the form of buttons, switches or dials to allow a person to interact with the device. The buttons, switches or dials may be physical devices, or software devices accessible via a touch screen. The buttons, switches or dials may, in one form, be physically connected to the external housing 4010, or may, in another form, be in wireless communication with a receiver that is in electrical connection to the central controller 4230.

[0261] In one form, the input device 4220 may be constructed and arranged to allow a person to select a value and/or a menu option.

5.4.2.3 Central Controller

[0262] In one form of the present technology, the central controller 4230 is one or a plurality of processors suitable to control an RPT device 4000.

[0263] Suitable processors may include an x86 INTEL processor, a processor based on ARM® Cortex®-M processor from ARM Holdings such as an STM32 series microcontroller from ST MICROELECTRONIC. In certain alternative forms of the present technology, a 32-bit RISC CPU, such as an STR9 series microcontroller from ST MICROELECTRONICS or a 16-bit RISC CPU such as a processor from the MSP430 family of microcontrollers, manufactured by TEXAS INSTRUMENTS may also be suitable.

[0264] In one form of the present technology, the central controller 4230 is a dedicated electronic circuit.

[0265] In one form, the central controller 4230 is an application-specific integrated circuit. In another form, the central controller 4230 comprises discrete electronic components.

[0266] The central controller 4230 may be configured to receive input signal(s) from one or more transducers 4270, one or more input devices 4220, and the humidifier 5000.

[0267] The central controller 4230 may be configured to provide output signal(s) to one or more of an output device 4290, a therapy device controller 4240, a data communication interface 4280, and the humidifier 5000.

[0268] In some forms of the present technology, the central controller 4230 is configured to implement the one or more methodologies described herein, such as the one or more algorithms 4300 expressed as computer programs stored in a non-transitory computer readable storage medium, such as memory 4260. In some forms of the present technology, the central controller 4230 may be integrated with an RPT device 4000. However, in some forms of the present technology, some methodologies may be performed by a remotely located device. For example, the remotely located device may determine control settings for a ventilator or detect respiratory related events by analysis of stored data such as from any of the sensors described herein.

5.4.2.4 Clock

[0269] The RPT device 4000 may include a clock 4232 that is connected to the central controller 4230.

5.4.2.5 Therapy Device Controller

[0270] In one form of the present technology, therapy device controller 4240 is a therapy control module 4330 that forms part of the algorithms 4300 executed by the central controller 4230.

[0271] In one form of the present technology, therapy device controller 4240 is a dedicated motor control integrated circuit. For example, in one form a MC33035 brushless DC motor controller, manufactured by ONSEMI is used.

5.4.2.6 Protection Circuits

[0272] The one or more protection circuits 4250 in accordance with the present technology may comprise an electrical protection circuit, a temperature and/or pressure safety circuit.

5.4.2.7 Memory

[0273] In accordance with one form of the present technology the RPT device 4000 includes memory 4260, e.g., non-volatile memory. In some forms, memory 4260 may include battery powered static RAM. In some forms, memory 4260 may include volatile RAM.

[0274] Memory 4260 may be located on the PCBA 4202. Memory 4260 may be in the form of EEPROM, or NAND flash.

[0275] Additionally or alternatively, RPT device 4000 includes a removable form of memory 4260, for example a memory card made in accordance with the Secure Digital (SD) standard.

[0276] In one form of the present technology, the memory 4260 acts as a non-transitory computer readable storage medium on which is stored computer program instructions expressing the one or more methodologies described herein, such as the one or more algorithms 4300.

5.4.2.8 Data Communication Systems

[0277] In one form of the present technology, a data communication interface 4280 is provided, and is connected to the central controller 4230. Data communication interface 4280 may be connectable to a remote external communication network 4282 and/or a local external communication network 4284. The remote external communication network 4282 may be connectable to a remote external device 4286. The local external communication network 4284 may be connectable to a local external device 4288.

[0278] In one form, data communication interface 4280 is part of the central controller 4230. In another form, data communication interface 4280 is separate from the central controller 4230, and may comprise an integrated circuit or a processor.

[0279] In one form, remote external communication network 4282 is the Internet. The data communication interface 4280 may use wired communication (e.g. via Ethernet, or optical fibre) or a wireless protocol (e.g. CDMA, GSM, LTE) to connect to the Internet.

[0280] In one form, local external communication network 4284 utilises one or more communication standards, such as Bluetooth, or a consumer infrared protocol.

[0281] In one form, remote external device 4286 is one or more computers, for example a cluster of networked computers. In one form, remote external device 4286 may be virtual computers, rather than physical computers. In either case, such a remote external device 4286 may be accessible to an appropriately authorised person such as a clinician.

[0282] The local external device 4288 may be a personal computer, mobile phone, tablet or remote control.

5.4.2.9 Output Devices Including Optional Display, Alarms

[0283] An output device 4290 in accordance with the present technology may take the form of one or more of a visual, audio and haptic unit. A visual display may be a Liquid Crystal Display (LCD) or Light Emitting Diode (LED) display.

5.4.2.9.1 Display Driver

[0284] A display driver 4292 receives as an input the characters, symbols, or images intended for display on the display 4294, and converts them to commands that cause the display 4294 to display those characters, symbols, or images.

5.4.2.9.2 Display

[0285] A display 4294 is configured to visually display characters, symbols, or images in response to commands received from the display driver 4292. For example, the display 4294 may be an eight-segment display, in which case the display driver 4292 converts each character or symbol, such as the figure “0”, to eight logical signals indicating whether the eight respective segments are to be activated to display a particular character or symbol.

5.4.3 RPT Device Algorithms

[0286] As mentioned above, in some forms of the present technology, the central controller 4230 may be configured to implement one or more algorithms 4300 expressed as computer programs stored in a non-transitory computer readable storage medium, such as memory 4260. The algorithms 4300 are generally grouped into groups referred to as modules.

[0287] In other forms of the present technology, some portion or all of the algorithms 4300 may be implemented by a controller of an external device such as the local external device 4288 or the remote external device 4286. In such forms, data representing the input signals and / or intermediate algorithm outputs necessary for the portion of the algorithms 4300 to be executed at the external device may be communicated to the external device via the local external communication network 4284 or the remote external communication network 4282. In such forms, the portion of the algorithms 4300 to be executed at the external device may be expressed as computer programs stored in a non-transitory computer readable storage medium accessible to the controller of the external device. Such programs configure the controller of the external device to execute the portion of the algorithms 4300.

[0288] In such forms, the therapy parameters generated by the external device via the therapy engine module 4320 (if such forms part of the portion of the algorithms 4300 executed by the external device) may be communicated to the central controller 4230 to be passed to the therapy control module 4330.

5.4.3.1 Pre-Processing Module

[0289] A pre-processing module 4310 in accordance with one form of the present technology receives as an input a signal from a transducer 4270, for example a flow rate sensor 4274 or pressure sensor 4272, and performs one or more process steps to calculate one or more output values that will be used as an input to another module, for example a therapy engine module 4320.

[0290] In one form of the present technology, the output values include the interface pressure Pm, the respiratory flow rate Qr, and the leak flow rate Ql.

[0291] In various forms of the present technology, the pre-processing module 4310 comprises one or more of the following algorithms: interface pressure estimation 4312, vent flow rate estimation 4314, leak flow rate estimation 4316, and respiratory flow rate estimation 4318.

5.4.3.1.1 Interface Pressure Estimation

[0292] In one form of the present technology, an interface pressure estimation algorithm 4312 receives as inputs a signal from the pressure sensor 4272 indicative of the pressure in the pneumatic path proximal to an outlet of the pneumatic block (the device pressure Pd) and a signal from the flow rate sensor 4274 representative of the flow rate of the airflow leaving the RPT device 4000 (the device flow rate Qd). The device flow rate Qd, absent any supplementary gas 4180, may be used as the total flow rate Qt. The interface pressure algorithm 4312 estimates the pressure drop ΔP through the air circuit 4170. The dependence of the pressure drop ΔP on the total flow rate Qt may be modelled for the particular air circuit 4170 by a pressure drop characteristic ΔP(Q). The interface pressure estimation algorithm, 4312 then provides as an output an estimated pressure, Pm, in the patient interface 3000 or 3800. The pressure, Pm, in the patient interface 3000 or 3800 may be estimated as the device pressure Pd minus the air circuit pressure drop ΔP.

5.4.3.1.2 Vent Flow Rate Estimation

[0293] In one form of the present technology, a vent flow rate estimation algorithm 4314 receives as an input an estimated pressure, Pm, in the patient interface 3000 or 3800 from the interface pressure estimation algorithm 4312 and estimates a vent flow rate of air, Qv, from a vent 3400 in a patient interface 3000 or 3800. The dependence of the vent flow rate Qv on the interface pressure Pm for the particular vent 3400 in use may be modelled by a vent characteristic Qv(Pm).

5.4.3.1.3 Leak Flow Rate Estimation

[0294] In one form of the present technology, a leak flow rate estimation algorithm 4316 receives as an input a total flow rate, Qt, and a vent flow rate Qv, and provides as an output an estimate of the leak flow rate Ql. In one form, the leak flow rate estimation algorithm estimates the leak flow rate Ql by calculating an average of the difference between total flow rate Qt and vent flow rate Qv over a period sufficiently long to include several breathing cycles, e.g. about 10 seconds.

[0295] In one form, the leak flow rate estimation algorithm 4316 receives as an input a total flow rate Qt, a vent flow rate Qv, and an estimated pressure, Pm, in the patient interface 3000 or 3800, and provides as an output a leak flow rate Ql, by calculating a leak conductance, and determining a leak flow rate Ql to be a function of leak conductance and pressure, Pm. Leak conductance is calculated as the quotient of low pass filtered non-vent flow rate equal to the difference between total flow rate Qt and vent flow rate Qv, and low pass filtered square root of pressure Pm, where the low pass filter time constant has a value sufficiently long to include several breathing cycles, e.g. about 10 seconds. The leak flow rate Ql may be estimated as the product of leak conductance and a function of pressure, Pm.

5.4.3.1.4 Respiratory Flow Rate Estimation

[0296] In one form of the present technology, a respiratory flow rate estimation algorithm 4318 receives as an input a total flow rate, Qt, a vent flow rate, Qv, and a leak flow rate, Ql, and estimates a respiratory flow rate of air, Qr, to the patient, by subtracting the vent flow rate Qv and the leak flow rate Ql from the total flow rate Qt.

5.4.3.2 Therapy Engine Module

[0297] In one form of the present technology, a therapy engine module 4320 receives as inputs one or more of a pressure, Pm, in a patient interface 3000 or 3800, and a respiratory flow rate of air to a patient, Qr, and provides as an output one or more therapy parameters.

[0298] In one form of the present technology, a therapy parameter is a treatment pressure Pt.

[0299] In one form of the present technology, therapy parameters are one or more of an amplitude of a pressure variation, a base pressure, and a target ventilation.

[0300] In various forms, the therapy engine module 4320 comprises one or more of the following algorithms: phase determination 4321, waveform determination 4322, ventilation determination 4323, inspiratory flow limitation determination 4324, apnea / hypopnea determination 4325, snore determination 4326, airway patency determination 4327, target ventilation determination 4328, and therapy parameter determination 4329.

5.4.3.2.1 Phase Determination

[0301] In one form of the present technology, the RPT device 4000 does not determine phase.

[0302] In one form of the present technology, a phase determination algorithm 4321 receives as an input a signal indicative of respiratory flow rate, Qr, and provides as an output a phase Φ of a current breathing cycle of a patient 1000.

[0303] In some forms, known as discrete phase determination, the phase output Φ is a discrete variable. One implementation of discrete phase determination provides a bi-valued phase output Φ with values of either inhalation or exhalation, for example represented as values of 0 and 0.5 revolutions respectively, upon detecting the start of spontaneous inhalation and exhalation respectively. RPT devices 4000 that “trigger” and “cycle” effectively perform discrete phase determination, since the trigger and cycle points are the instants at which the phase changes from exhalation to inhalation and from inhalation to exhalation, respectively. In one implementation of bi-valued phase determination, the phase output Φ is determined to have a discrete value of 0 (thereby “triggering” the RPT device 4000) when the respiratory flow rate Qr has a value that exceeds a positive threshold, and a discrete value of 0.5 revolutions (thereby “cycling” the RPT device 4000) when a respiratory flow rate Qr has a value that is more negative than a negative threshold. The inhalation time Ti and the exhalation time Te may be estimated as typical values over many respiratory cycles of the time spent with phase Φ equal to 0 (indicating inspiration) and 0.5 (indicating expiration) respectively.

[0304] Another implementation of discrete phase determination provides a tri-valued phase output Φ with a value of one of inhalation, mid-inspiratory pause, and exhalation.

[0305] In other forms, known as continuous phase determination, the phase output Φ is a continuous variable, for example varying from 0 to 1 revolutions, or 0 to 2π radians. RPT devices 4000 that perform continuous phase determination may trigger and cycle when the continuous phase reaches 0 and 0.5 revolutions, respectively. In one implementation of continuous phase determination, a continuous value of phase Φ is determined using a fuzzy logic analysis of the respiratory flow rate Qr. A continuous value of phase determined in this implementation is often referred to as “fuzzy phase”. In one implementation of a fuzzy phase determination algorithm 4321, the following rules are applied to the respiratory flow rate Qr: [0306] 1. If the respiratory flow rate is zero and increasing fast then the phase is 0 revolutions. [0307] 2. If the respiratory flow rate is large positive and steady then the phase is 0.25 revolutions. [0308] 3. If the respiratory flow rate is zero and falling fast, then the phase is 0.5 revolutions. [0309] 4. If the respiratory flow rate is large negative and steady then the phase is 0.75 revolutions. [0310] 5. If the respiratory flow rate is zero and steady and the 5-second low-pass filtered absolute value of the respiratory flow rate is large then the phase is 0.9 revolutions. [0311] 6. If the respiratory flow rate is positive and the phase is expiratory, then the phase is 0 revolutions. [0312] 7. If the respiratory flow rate is negative and the phase is inspiratory, then the phase is 0.5 revolutions. [0313] 8. If the 5-second low-pass filtered absolute value of the respiratory flow rate is large, the phase is increasing at a steady rate equal to the patient’s breathing rate, low-pass filtered with a time constant of 20 seconds.

[0314] The output of each rule may be represented as a vector whose phase is the result of the rule and whose magnitude is the fuzzy extent to which the rule is true. The fuzzy extent to which the respiratory flow rate is “large”, “steady”, etc. is determined with suitable membership functions. The results of the rules, represented as vectors, are then combined by some function such as taking the centroid. In such a combination, the rules may be equally weighted, or differently weighted.

[0315] In another implementation of continuous phase determination, the phase Φ is first discretely estimated from the respiratory flow rate Qr as described above, as are the inhalation time Ti and the exhalation time Te. The continuous phase Φ at any instant may be determined as the half the proportion of the inhalation time Ti that has elapsed since the previous trigger instant, or 0.5 revolutions plus half the proportion of the exhalation time Te that has elapsed since the previous cycle instant (whichever instant was more recent).

5.4.3.2.2 Waveform Determination

[0316] In one form of the present technology, the therapy parameter determination algorithm 4329 provides an approximately constant treatment pressure throughout a respiratory cycle of a patient.

[0317] In other forms of the present technology, the therapy control module 4330 controls the pressure generator 4140 to provide a treatment pressure Pt that varies as a function of phase Φ of a respiratory cycle of a patient according to a waveform template II (Φ).

[0318] In one form of the present technology, a waveform determination algorithm 4322 provides a waveform template Π(Φ) with values in the range [0, 1] on the domain of phase values Φ provided by the phase determination algorithm 4321 to be used by the therapy parameter determination algorithm 4329.

[0319] In one form, suitable for either discrete or continuously-valued phase, the waveform template Π(Φ) is a square-wave template, having a value of 1 for values of phase up to and including 0.5 revolutions, and a value of 0 for values of phase above 0.5 revolutions. In one form, suitable for continuously-valued phase, the waveform template Π(Φ) comprises two smoothly curved portions, namely a smoothly curved (e.g. raised cosine) rise from 0 to 1 for values of phase up to 0.5 revolutions, and a smoothly curved (e.g. exponential) decay from 1 to 0 for values of phase above 0.5 revolutions. In one form, suitable for continuously-valued phase, the waveform template Π(Φ) is based on a square wave, but with a smooth rise from 0 to 1 for values of phase up to a “rise time” that is less than 0.5 revolutions, and a smooth fall from 1 to 0 for values of phase within a “fall time” after 0.5 revolutions, with a “fall time” that is less than 0.5 revolutions.

[0320] In some forms of the present technology, the waveform determination algorithm 4322 selects a waveform template Π(Φ) from a library of waveform templates, dependent on a setting of the RPT device. Each waveform template Π(Φ) in the library may be provided as a lookup table of values Π against phase values Φ. In other forms, the waveform determination algorithm 4322 computes a waveform template Π(Φ) “on the fly” using a predetermined functional form, possibly parametrised by one or more parameters (e.g. time constant of an exponentially curved portion). The parameters of the functional form may be predetermined or dependent on a current state of the patient 1000.

[0321] In some forms of the present technology, suitable for discrete bi-valued phase of either inhalation (Φ = 0 revolutions) or exhalation (Φ = 0.5 revolutions), the waveform determination algorithm 4322 computes a waveform template Π “on the fly” as a function of both discrete phase Φ and time t measured since the most recent trigger instant. In one such form, the waveform determination algorithm 4322 computes the waveform template Π(Φ, t) in two portions (inspiratory and expiratory) as follows:

${\displaystyle .Math.\left(\Phi ,t\right)}=\left\{\begin{array}{cc}{\displaystyle .Math.{}_i\left(t\right),}& \Phi =0\\ {\displaystyle .Math.{}_e\left(t-T_i\right),}& \Phi =0.5\end{array}\right.$

[0322] where Π.sub.i(t) and Π.sub.e(t) are inspiratory and expiratory portions of the waveform template Π(Φ, t). In one such form, the inspiratory portion Π.sub.i(t) of the waveform template is a smooth rise from 0 to 1 parametrised by a rise time, and the expiratory portion Π.sub.e(t) of the waveform template is a smooth fall from 1 to 0 parametrised by a fall time.

5.4.3.2.3 Ventilation Determination

[0323] In one form of the present technology, a ventilation determination algorithm 4323 receives an input a respiratory flow rate Qr, and determines a measure indicative of current patient ventilation, Vent.

[0324] In some implementations, the ventilation determination algorithm 4323 determines a measure of ventilation Vent that is an estimate of actual patient ventilation. One such implementation is to take half the absolute value of respiratory flow rate, Qr, optionally filtered by low-pass filter such as a second order Bessel low-pass filter with a corner frequency of 0.11 Hz.

[0325] In other implementations, the ventilation determination algorithm 4323 determines a measure of ventilation Vent that is broadly proportional to actual patient ventilation. One such implementation estimates peak respiratory flow rate Qpeak over the inspiratory portion of the cycle. This and many other procedures involving sampling the respiratory flow rate Qr produce measures which are broadly proportional to ventilation, provided the flow rate waveform shape does not vary very much (here, the shape of two breaths is taken to be similar when the flow rate waveforms of the breaths normalised in time and amplitude are similar). Some simple examples include the median positive respiratory flow rate, the median of the absolute value of respiratory flow rate, and the standard deviation of flow rate. Arbitrary linear combinations of arbitrary order statistics of the absolute value of respiratory flow rate using positive coefficients, and even some using both positive and negative coefficients, are approximately proportional to ventilation. Another example is the mean of the respiratory flow rate in the middle K proportion (by time) of the inspiratory portion, where 0 < K < 1. There is an arbitrarily large number of measures that are exactly proportional to ventilation if the flow rate shape is constant.

5.4.3.2.4 Determination of Inspiratory Flow Limitation

[0326] In one form of the present technology, the central controller 4230 executes an inspiratory flow limitation determination algorithm 4324 for the determination of the extent of inspiratory flow limitation.

[0327] In one form, the inspiratory flow limitation determination algorithm 4324 receives as an input a respiratory flow rate signal Qr and provides as an output a metric of the extent to which the inspiratory portion of the breath exhibits inspiratory flow limitation.

[0328] In one form of the present technology, the inspiratory portion of each breath is identified by a zero-crossing detector. A number of evenly spaced points (for example, sixty-five), representing points in time, are interpolated by an interpolator along the inspiratory flow rate-time curve for each breath. The curve described by the points is then scaled by a scalar to have unity length (duration/period) and unity area to remove the effects of changing breathing rate and depth. The scaled breaths are then compared in a comparator with a pre-stored template representing a normal unobstructed breath, similar to the inspiratory portion of the breath shown in FIG. 6A. Breaths deviating by more than a specified threshold (typically 1 scaled unit) at any time during the inspiration from this template, such as those due to coughs, sighs, swallows and hiccups, as determined by a test element, are rejected. For non-rejected data, a moving average of the first such scaled point is calculated by the central controller 4230 for the preceding several inspiratory events. This is repeated over the same inspiratory events for the second such point, and so on. Thus, for example, sixty five scaled data points are generated by the central controller 4230, and represent a moving average of the preceding several inspiratory events, e.g., three events. The moving average of continuously updated values of the (e.g., sixty five) points are hereinafter called the "scaled flow rate ", designated as Qs(t). Alternatively, a single inspiratory event can be utilised rather than a moving average.

[0329] From the scaled flow rate, two shape factors relating to the determination of partial obstruction may be calculated.

[0330] Shape factor 1 is the ratio of the mean of the middle (e.g. thirty-two) scaled flow rate points to the mean overall (e.g. sixty-five) scaled flow rate points. Where this ratio is in excess of unity, the breath will be taken to be normal. Where the ratio is unity or less, the breath will be taken to be obstructed. A ratio of about 1.17 is taken as a threshold between partially obstructed and unobstructed breathing, and equates to a degree of obstruction that would permit maintenance of adequate oxygenation in a typical patient.

[0331] Shape factor 2 is calculated as the RMS deviation from unit scaled flow rate, taken over the middle (e.g. thirty two) points. An RMS deviation of about 0.2 units is taken to be normal. An RMS deviation of zero is taken to be a totally flow-limited breath. The closer the RMS deviation to zero, the breath will be taken to be more flow limited.

[0332] Shape factors 1 and 2 may be used as alternatives, or in combination. In other forms of the present technology, the number of sampled points, breaths and middle points may differ from those described above. Furthermore, the threshold values can be other than those described.

5.4.3.2.5 Determination of Apneas and Hypopneas

[0333] In one form of the present technology, the central controller 4230 executes an apnea / hypopnea determination algorithm 4325 for the determination of the presence of apneas and/or hypopneas.

[0334] In one form, the apnea / hypopnea determination algorithm 4325 receives as an input a respiratory flow rate signal Qr and provides as an output a flag that indicates that an apnea or a hypopnea has been detected.

[0335] In one form, an apnea will be said to have been detected when a function of respiratory flow rate Qr falls below a flow rate threshold for a predetermined period of time. The function may determine a peak flow rate, a relatively short-term mean flow rate, or a flow rate intermediate of relatively short-term mean and peak flow rate, for example an RMS flow rate. The flow rate threshold may be a relatively long-term measure of flow rate.

[0336] In one form, a hypopnea will be said to have been detected when a function of respiratory flow rate Qr falls below a second flow rate threshold for a predetermined period of time. The function may determine a peak flow, a relatively short-term mean flow rate, or a flow rate intermediate of relatively short-term mean and peak flow rate, for example an RMS flow rate. The second flow rate threshold may be a relatively long-term measure of flow rate. The second flow rate threshold is greater than the flow rate threshold used to detect apneas.

5.4.3.2.6 Determination of Snore

[0337] In one form of the present technology, the central controller 4230 executes one or more snore determination algorithms 4326 for the determination of the extent of snore.

[0338] In one form, the snore determination algorithm 4326 receives as an input a respiratory flow rate signal Qr and provides as an output a metric of the extent to which snoring is present.

[0339] The snore determination algorithm 4326 may comprise the step of determining the intensity of the flow rate signal in the range of 30-300 Hz. Further, the snore determination algorithm 4326 may comprise a step of filtering the respiratory flow rate signal Qr to reduce background noise, e.g., the sound of airflow in the system from the blower.

5.4.3.2.7 Determination of Airway Patency

[0340] In one form of the present technology, the central controller 4230 executes one or more airway patency determination algorithms 4327 for the determination of the extent of airway patency.

[0341] In one form, the airway patency determination algorithm 4327 receives as an input a respiratory flow rate signal Qr, and determines the power of the signal in the frequency range of about 0.75 Hz and about 3 Hz. The presence of a peak in this frequency range is taken to indicate an open airway. The absence of a peak is taken to be an indication of a closed airway.

[0342] In one form, the frequency range within which the peak is sought is the frequency of a small forced oscillation in the treatment pressure Pt. In one implementation, the forced oscillation is of frequency 2 Hz with amplitude about 1 cmH.sub.2O.

[0343] In one form, airway patency determination algorithm 4327 receives as an input a respiratory flow rate signal Qr, and determines the presence or absence of a cardiogenic signal. The absence of a cardiogenic signal is taken to be an indication of a closed airway.

5.4.3.2.8 Determination of Target Ventilation

[0344] In one form of the present technology, the central controller 4230 takes as input the measure of current ventilation, Vent, and executes one or more target ventilation determination algorithms 4328 for the determination of a target value Vtgt for the measure of ventilation.

[0345] In some forms of the present technology, there is no target ventilation determination algorithm 4328, and the target value Vtgt is predetermined, for example by hard-coding during configuration of the RPT device 4000 or by manual entry through the input device 4220.

[0346] In other forms of the present technology, such as adaptive servo-ventilation (ASV), the target ventilation determination algorithm 4328 computes a target value Vtgt from a value Vtyp indicative of the typical recent ventilation of the patient.

[0347] In some forms of adaptive servo-ventilation, the target ventilation Vtgt is computed as a high proportion of, but less than, the typical recent ventilation Vtyp. The high proportion in such forms may be in the range (80%, 100%), or (85%, 95%), or (87%, 92%).

[0348] In other forms of adaptive servo-ventilation, the target ventilation Vtgt is computed as a slightly greater than unity multiple of the typical recent ventilation Vtyp.

[0349] The typical recent ventilation Vtyp is the value around which the distribution of the measure of current ventilation Vent over multiple time instants over some predetermined timescale tends to cluster, that is, a measure of the central tendency of the measure of current ventilation over recent history. In one implementation of the target ventilation determination algorithm 4328, the recent history is of the order of several minutes, but in any case should be longer than the timescale of Cheyne-Stokes waxing and waning cycles. The target ventilation determination algorithm 4328 may use any of the variety of well-known measures of central tendency to determine the typical recent ventilation Vtyp from the measure of current ventilation, Vent. One such measure is the output of a low-pass filter on the measure of current ventilation Vent, with time constant equal to one hundred seconds.

5.4.3.2.9 Determination of Therapy Parameters

[0350] In some forms of the present technology, the central controller 4230 executes one or more therapy parameter determination algorithms 4329 for the determination of one or more therapy parameters using the values returned by one or more of the other algorithms in the therapy engine module 4320.

[0351] In one form of the present technology, the therapy parameter is an instantaneous treatment pressure Pt. In one implementation of this form, the therapy parameter determination algorithm 4329 determines the treatment pressure Pt using the equation

$Pt=A{\displaystyle .Math.\left(\Phi ,t\right)P_0}$

[0352] where: [0353] A is the amplitude, [0354] Π(Φ, t) is the waveform template value (in the range 0 to 1) at the current value Φ of phase and t of time, and [0355] P.sub.0 is a base pressure.

[0356] If the waveform determination algorithm 4322 provides the waveform template Π(Φ, t) as a lookup table of values Π indexed by phase Φ, the therapy parameter determination algorithm 4329 applies equation (1) by locating the nearest lookup table entry to the current value Φ of phase returned by the phase determination algorithm 4321, or by interpolation between the two entries straddling the current value Φ of phase.

[0357] The values of the amplitude A and the base pressure P.sub.0 may be set by the therapy parameter determination algorithm 4329 depending on the chosen respiratory pressure therapy mode in the manner described below.

5.4.3.3 Therapy Control Module

[0358] The therapy control module 4330 in accordance with one aspect of the present technology receives as inputs the therapy parameters from the therapy parameter determination algorithm 4329 of the therapy engine module 4320, and controls the pressure generator 4140 to deliver a flow of air in accordance with the therapy parameters.

[0359] In one form of the present technology, the therapy parameter is a treatment pressure Pt, and the therapy control module 4330 controls the pressure generator 4140 to deliver a flow of air whose interface pressure Pm at the patient interface 3000 or 3800 is equal to the treatment pressure Pt.

5.4.3.4 Detection of Fault Conditions

[0360] In one form of the present technology, the central controller 4230 executes one or more methods 4340 for the detection of fault conditions. The fault conditions detected by the one or more methods 4340 may include at least one of the following: [0361] Power failure (no power, or insufficient power) [0362] Transducer fault detection [0363] Failure to detect the presence of a component [0364] Operating parameters outside recommended ranges (e.g. pressure, flow rate, temperature, PaO.sub.2) [0365] Failure of a test alarm to generate a detectable alarm signal.

[0366] Upon detection of the fault condition, the corresponding algorithm 4340 signals the presence of the fault by one or more of the following: [0367] Initiation of an audible, visual &/or kinetic (e.g. vibrating) alarm [0368] Sending a message to an external device [0369] Logging of the incident

5.5 Air Circuit

[0370] An air circuit 4170 in accordance with an aspect of the present technology is a conduit or a tube constructed and arranged to allow, in use, a flow of air to travel between two components such as RPT device 4000 and the patient interface 3000 or 3800.

[0371] In particular, the air circuit 4170 may be in fluid connection with the outlet of the pneumatic block 4020 and the patient interface. The air circuit may be referred to as an air delivery tube. In some cases there may be separate limbs of the circuit for inhalation and exhalation. In other cases a single limb is used.

[0372] In some forms, the air circuit 4170 may comprise one or more heating elements configured to heat air in the air circuit, for example to maintain or raise the temperature of the air. The heating element may be in a form of a heated wire circuit, and may comprise one or more transducers, such as temperature sensors. In one form, the heated wire circuit may be helically wound around the axis of the air circuit 4170. The heating element may be in communication with a controller such as a central controller 4230. One example of an air circuit 4170 comprising a heated wire circuit is described in U.S. Pat. 8,733,349, which is incorporated herewithin in its entirety by reference.

5.5.1 Supplementary Gas Delivery

[0373] In one form of the present technology, supplementary gas, e.g. oxygen, 4180 is delivered to one or more points in the pneumatic path, such as upstream of the pneumatic block 4020, to the air circuit 4170, and/or to the patient interface 3000 or 3800.

5.6 Respiratory Flow Therapy Modes

[0374] In some versions, the RPT may be configured with a flow control loop, such as with an estimate flow signal, to provide respiratory therapies with an interface to the patient’s airways that is ‘open’ (unsealed). The respiratory therapy may supplement the patient’s own spontaneous breathing with a controlled flow of conditioned or enriched gas. In one example, High Flow therapy (HFT) in controlled an entrance to the airway through an unsealed or open patient interface at a “treatment flow rate” that is held approximately constant throughout the respiratory cycle. The treatment flow rate is nominally set to exceed the patient’s peak inspiratory flow rate. As an alternative to constant flow rate, the treatment flow rate may follow a profile that varies over the respiratory cycle.

6 Humidifier

6.1.1 Humidifier Overview

[0375] Respiratory humidifiers are available in many forms and may be a standalone device that is coupled to an RPT device via an air circuit, is integrated with the RPT device or configured to be directly coupled to the relevant RPT device. While known passive humidifiers can provide some relief, generally a heated humidifier may be used to provide sufficient humidity and temperature to the air so that the patient will be comfortable. In examples, humidifiers comprise a water reservoir or tub having a capacity of several hundred milliliters (ml), a heating element for heating the water in the reservoir, a control to enable the level of humidification to be varied, a gas inlet to receive gas from the flow generator or RPT device, and a gas outlet adapted to be connected to an air circuit that delivers the humidified gas to the patient interface.

[0376] Heated passover humidification is one common form of humidification used with an RPT device. In such humidifiers the heating element may be incorporated in a heater plate which sits under, and is in thermal contact with, the water tub. Thus, heat is transferred from the heater plate to the water reservoir primarily by conduction. The air flow from the RPT device passes over the heated water in the water tub resulting in water vapour being taken up by the air flow. The ResMed H4i™ and HSi™ Humidifiers are examples of such heated passover humidifiers that are used in combination with ResMed S8 and S9 CPAP devices respectively.

[0377] Other humidifiers may also be used such as a bubble or diffuser humidifier, a jet humidifier or a wicking humidifier. In a bubble or diffuser humidifier the air is conducted below the surface of the water and allowed to bubble back to the top. A jet humidifier produces an aerosol of water and baffles or filters may be used so that the particles are either removed or evaporated before leaving the humidifier. A wicking humidifier uses a water absorbing material, such as sponge or paper, to absorb water by capillary action. The water absorbing material is placed within or adjacent at least a portion of the air flow path to allow evaporation of the water in the absorbing material to be taken up into the air flow.

[0378] An alternative form of humidification is provided by the ResMed HumiCare™ D900 humidifier that uses a CounterStream™ technology that directs the air flow over a large surface area in a first direction whilst supplying heated water to the large surface area in a second opposite direction. The ResMed HumiCare™ D900 humidifier may be used with a range of invasive and non-invasive ventilators.

[0379] In one form of the present technology there is provided a humidifier 5000 (e.g. as shown in FIG. 5A) to change the absolute humidity of air or gas for delivery to a patient relative to ambient air. Typically, the humidifier 5000 is used to increase the absolute humidity and increase the temperature of the flow of air (relative to ambient air) before delivery to the patient’s airways.

[0380] The humidifier 5000 may comprise a humidifier reservoir 5110, a humidifier inlet 5002 to receive a flow of air, and a humidifier outlet 5004 to deliver a humidified flow of air. In some forms, as shown in FIG. 5A and FIG. 5B, an inlet and an outlet of the humidifier reservoir 5110 may be the humidifier inlet 5002 and the humidifier outlet 5004 respectively. The humidifier 5000 may further comprise a humidifier base 5006, which may be adapted to receive the humidifier reservoir 5110 and comprise a heating element 5240.

6.1.2 Humidifier Components

6.1.2.1 Water Reservoir

[0381] According to one arrangement, the humidifier 5000 may comprise a water reservoir 5110 configured to hold, or retain, a volume of liquid (e.g. water) to be evaporated for humidification of the flow of air. The water reservoir 5110 may be configured to hold a predetermined maximum volume of water in order to provide adequate humidification for at least the duration of a respiratory therapy session, such as one evening of sleep. Typically, the reservoir 5110 is configured to hold several hundred millilitres of water, e.g. 300 millilitres (ml), 325 ml, 350 ml or 400 ml. In other forms, the humidifier 5000 may be configured to receive a supply of water from an external water source such as a building’s water supply system.

[0382] According to one aspect, the water reservoir 5110 is configured to add humidity to a flow of air from the RPT device 4000 as the flow of air travels therethrough. In one form, the water reservoir 5110 may be configured to encourage the flow of air to travel in a tortuous path through the reservoir 5110 while in contact with the volume of water therein.

[0383] According to one form, the reservoir 5110 may be removable from the humidifier 5000, for example in a lateral direction as shown in FIG. 5A and FIG. 5B.

[0384] The reservoir 5110 may also be configured to discourage egress of liquid therefrom, such as when the reservoir 5110 is displaced and/or rotated from its normal, working orientation, such as through any apertures and/or in between its subcomponents. As the flow of air to be humidified by the humidifier 5000 is typically pressurised, the reservoir 5110 may also be configured to prevent losses in pneumatic pressure through leak and/or flow impedance.

6.1.2.2 Conductive Portion

[0385] According to one arrangement, the reservoir 5110 comprises a conductive portion 5120 configured to allow efficient transfer of heat from the heating element 5240 to the volume of liquid in the reservoir 5110. In one form, the conductive portion 5120 may be arranged as a plate, although other shapes may also be suitable. All or a part of the conductive portion 5120 may be made of a thermally conductive material such as aluminium (e.g. approximately 2 mm thick, such as 1 mm, 1.5 mm, 2.5 mm or 3 mm), another heat conducting metal or some plastics. In some cases, suitable heat conductivity may be achieved with less conductive materials of suitable geometry.

6.1.2.3 Humidifier Reservoir Dock

[0386] In one form, the humidifier 5000 may comprise a humidifier reservoir dock 5130 (as shown in FIG. 5B) configured to receive the humidifier reservoir 5110. In some arrangements, the humidifier reservoir dock 5130 may comprise a locking feature such as a locking lever 5135 configured to retain the reservoir 5110 in the humidifier reservoir dock 5130.

6.1.2.4 Water Level Indicator

[0387] The humidifier reservoir 5110 may comprise a water level indicator 5150 as shown in FIGS. 5A-5B. In some forms, the water level indicator 5150 may provide one or more indications to a user such as the patient 1000 or a care giver regarding a quantity of the volume of water in the humidifier reservoir 5110. The one or more indications provided by the water level indicator 5150 may include an indication of a maximum, predetermined volume of water, any portions thereof, such as 25%, 50% or 75% or volumes such as 200 ml, 300 ml or 400 ml.

6.1.2.5 Humidifier Transducer(s)

[0388] The humidifier 5000 may comprise one or more humidifier transducers (sensors) 5210 instead of, or in addition to, transducers 4270 described above. Humidifier transducers 5210 may include one or more of an air pressure sensor 5212, an air flow rate transducer 5214, a temperature sensor 5216, or a humidity sensor 5218 as shown in FIG. 5C. A humidifier transducer 5210 may produce one or more output signals which may be communicated to a controller such as the central controller 4230 and/or the humidifier controller 5250. In some forms, a humidifier transducer may be located externally to the humidifier 5000 (such as in the air circuit 4170) while communicating the output signal to the controller.

6.1.2.5.1 Pressure Transducer

[0389] One or more pressure transducers 5212 may be provided to the humidifier 5000 in addition to, or instead of, a pressure sensor 4272 provided in the RPT device 4000.

6.1.2.5.2 Flow Rate Transducer

[0390] One or more flow rate transducers 5214 may be provided to the humidifier 5000 in addition to, or instead of, a flow rate sensor 4274 provided in the RPT device 4000.

6.1.2.5.3 Temperature Transducer

[0391] The humidifier 5000 may comprise one or more temperature transducers 5216. The one or more temperature transducers 5216 may be configured to measure one or more temperatures such as of the heating element 5240 and/or of the flow of air downstream of the humidifier outlet 5004. In some forms, the humidifier 5000 may further comprise a temperature sensor 5216 to detect the temperature of the ambient air.

6.1.2.5.4 Humidity Transducer

[0392] In one form, the humidifier 5000 may comprise one or more humidity sensors 5218 to detect a humidity of a gas, such as the ambient air. The humidity sensor 5218 may be placed towards the humidifier outlet 5004 in some forms to measure a humidity of the gas delivered from the humidifier 5000. The humidity sensor may be an absolute humidity sensor or a relative humidity sensor.

6.1.2.6 Heating Element

[0393] A heating element 5240 may be provided to the humidifier 5000 in some cases to provide a heat input to one or more of the volume of water in the humidifier reservoir 5110 and/or to the flow of air. The heating element 5240 may comprise a heat generating component such as an electrically resistive heating track. One suitable example of a heating element 5240 is a layered heating element such as one described in the PCT Pat. Application Publication No. WO 2012/171072, which is incorporated herewith by reference in its entirety.

[0394] In some forms, the heating element 5240 may be provided in the humidifier base 5006 where heat may be provided to the humidifier reservoir 5110 primarily by conduction as shown in FIG. 5B.

6.1.2.7 Humidifier Controller

[0395] According to one arrangement of the present technology, a humidifier 5000 may comprise a humidifier controller 5250 as shown in FIG. 5C. In one form, the humidifier controller 5250 may be a part of the central controller 4230. In another form, the humidifier controller 5250 may be a separate controller, which may be in communication with the central controller 4230.

[0396] In one form, the humidifier controller 5250 may receive as inputs measures of properties (such as temperature, humidity, pressure and/or flow rate), for example of the flow of air, the water in the reservoir 5110 and/or the humidifier 5000. The humidifier controller 5250 may also be configured to execute or implement humidifier algorithms and/or deliver one or more output signals.

[0397] As shown in FIG. 5C, the humidifier controller 5250 may comprise one or more controllers, such as a central humidifier controller 5251, a heated air circuit controller 5254 configured to control the temperature of a heated air circuit 4171 and/or a heating element controller 5252 configured to control the temperature of a heating element 5240.

6.1.2.8 Releasable Connection to RPT Device

[0398] FIGS. 5D to 5F show a further RPT device 4000 according to another form of the present technology. The device includes an external housing 4010 which contains a pressure generator 4140 (not shown) for producing a flow of breathable gas at a positive pressure. For example, the pressure generator 4140 may be a controllable blower. The device 4000 also comprises input devices 4220 in the form of buttons, and dials, and output devices 4290 in the form of a display. The input devices 4220 and output devices 4290 together provide the user with a user interface for controlling and configuring the device 4000.

[0399] The device 4000 also comprises an outlet 4130 for supplying the flow of breathable gas to one or more downstream devices which are fluidly connected to the device 4000. In one form of the technology, the device 4000 is configured to releasably connect to a releasable component in the form of humidifier 5000. The releasable connection between the device 4000 and the humidifier 5000 may be provided by a mechanical connection mechanism which, when engaged, aligns the device 4000 and humidifier 5000 in such a way that an outlet 4130 of the device 4000 is fluidly connected with an inlet 5002 of the humidifier 5000 and one or more electrical connections 4296 of the device 4000 are electrically connected to corresponding electrical connections on the humidifier 5000.

[0400] The humidifier has a humidifier housing 5300 which is separate to the external housing 4010 of the device 4000. The humidifier housing 5300 contains a water reservoir 5110 and a heating element 5240 (not shown) configured to heat the water contained in the water reservoir 5110 to thereby facilitate humidification of the flow of breathable gas. In this example, the water reservoir 5110 may be removed from the humidifier housing 5300 by opening the lid or top cover 5306 of the humidifier 5000. In alternative examples, the water reservoir 5110 may be removed through an end or side of the humidifier 5000.

6.1.3 Liquid Trap

[0401] According to one aspect of the present technology, as shown in FIG. 5G, a humidifier 5000 may have a body comprising an external housing 5300. Referring to FIG. 5H, the housing 5300 may be formed in two parts, an upper portion 5302 and a lower portion 5304. The body of humidifier 5000 further comprises a chassis 5310.

[0402] Reference to a chassis herein should be understood to mean a supporting frame of a structure - i.e. a structural element configured to support one or more other components, more particularly one or more internal components of the humidifier 5000. Reference to a housing should be understood to mean an element that covers or protects other components of a structure. In the example of FIGS. 5G to 5I, the housing 5300 is provided to at least partially cover or protect the chassis 5310. In alternative examples, the humidifier 5000 may comprise a housing 5310 configured to act as a chassis 5310. In alternative examples, the humidifier 5000 may comprise a chassis 5310 without a separate housing per se.

[0403] In examples, the humidifier 5000 comprises a removable container in the form of water reservoir 5110. The chassis 5310 is configured to locate and support the removable reservoir 5110 in use. In the example shown in FIG. 5H, the reservoir 5110 is inserted and removed from an end of the humidifier. In alternative examples, the reservoir 5110 may be removed from a side of the humidifier 5000 (i.e. laterally), or from above or below (i.e. vertically). PCT Pat. Application Publication No. WO 2018/094452 Al describes exemplary arrangements for a humidifier having a removable water reservoir, the contents of which are incorporated herein by reference in their entirety.

[0404] In alternative examples, the chassis 5310 may comprise a chamber which functions as the water reservoir 5110 - i.e. is integrated with the chassis 5310 rather than being removable.

[0405] According to one aspect of the present technology, as shown in FIG. 5G, the humidifier 5000 comprises a closure element in the form of an end cap 5330. In this example the end cap 5330 is configured to seal against the housing 5300 and the chassis 5310, as described further below.

[0406] In examples, the end cap 5330 has a main cap wall 5332 comprising an air inlet port 5334 configured to be connected to a source of a flow of air at positive pressure, for example RPT device 4000. The air inlet port 5334 comprises an inner surface 5336 and an external annular port wall 5338 extending from the main cap wall 5332. The end cap 5330 further comprises an inner peripheral wall 5340 surrounding the air inlet port 5334 and extending towards the chassis 5310. In this example, the inner peripheral wall 5340 is annular.

[0407] In examples, the chassis 5310 has a vertical chassis wall 5312 comprising a chamber inlet port 5314. In the example of FIGS. 5G to 5I, the chamber inlet port 5314 pneumatically connects to an inlet port of the reservoir 5510. A chassis peripheral wall 5316 surrounds the chamber inlet port 5314 and extends towards the end cap 5330. In this example, the chassis peripheral wall 5316 is annular.

[0408] In examples, a free end 5318 of the chassis peripheral wall 5316 overlaps a free end 5342 of the inner peripheral wall 5340. A resilient seal 5360 is provided between the chassis peripheral wall 5316 and the inner peripheral wall 5340 to seal the space between the air inlet port 5334 and the chamber inlet port 5314. This provides a gas flow path between the air inlet port 5334 and the chamber inlet port 5314, and forms a liquid trap 5380 for retention of a volume of water spilled through the chamber inlet port 5314.

[0409] There are various circumstances in which water may pass through the chamber inlet port 5314 from the reservoir 5110, including knocking of the humidifier 5000 or a stand on which it sits to produce a sloshing effect, or tipping of the humidifier 5000 as it is shifted or re-oriented. The liquid trap 5380 is provided to retain a volume of this spilled water to reduce the likelihood of water reaching other components of the system upstream, more particularly the RPT device 4000.

[0410] Further, the liquid trap 5380 protects the space between the chassis 5310 and the end cap 5300 below the liquid trap 5380. Humidifier components which might otherwise be susceptible to water damage (for example electrical components) may be positioned in this space.

6.1.3.1 Resilient Seal

[0411] As shown in FIG. 5G, the resilient seal 5360 comprises a liquid trap portion 5362 positioned between the chassis peripheral wall 5316 and the inner peripheral wall 5340. The liquid trap portion 5362 is tubular in form, and covers an interior surface of the inner peripheral wall 5340. The liquid trap seal portion 5362 further comprises a first lip 5364 projecting radially inwardly to bear against an external surface of the chassis peripheral wall 5316. The first lip 5364 projects at an angle back towards the end cap 5330.

[0412] The resilient seal 5360 further comprises an air inlet port portion 5366 provided on the inner surface 5336 of the air inlet port 5334. The air inlet port portion 5366 comprises a second lip 5368 projecting radially inwardly at an angle back towards the chassis 5310. The resilient seal 5360 further comprises a flange portion 5370 between the air inlet port portion 5366 and the liquid trap portion 5362. In the example shown, the flange portion 5370 covers an inner surface of the main cap wall 5332 between the air inlet port 5334 and the inner peripheral wall 5340.

[0413] In examples each of the inner peripheral wall 5340 and the chassis peripheral wall 5316 are circular - i.e. generally take the form of cylindrical tubes. The liquid trap seal portion 5362 of the resilient seal 5360 is complementary in shape - i.e. is also a cylindrical tube. This circular geometry may assist with forming the seal therebetween.

[0414] In the example shown, the resilient seal 5360 comprises a peripheral seal portion 5372 formed as a unitary part. The peripheral seal portion 5372 is provided between the housing 5300 and the end cap 5330 to seal at least a portion of a periphery of the end cap 5330.

[0415] In examples, the resilient seal may be made of a silicone, a thermoplastic elastomer, or any other suitable resilient material.

[0416] In examples, the resilient seal 5360 may be overmolded to the end cap 5530. In alternative examples the resilient seal 5360 and the end cap 5530 may be manufactured separately and subsequently assembled.

[0417] In an alternate example, a first resilient seal may be provided between the chassis peripheral wall 5316 and the inner peripheral wall 5340, and one or more further resilient seals may be used to provide the functions of the air inlet port portion 5366 and/or the peripheral seal portion 5372. For example, the first resilient seal may be an O-ring.

[0418] In alternative examples, the chassis peripheral wall 5316 may seal directly against the inner peripheral wall 5340. For example, an engineering fit between the chassis peripheral wall 5316 and the inner peripheral wall 5340 may be used to produce a seal.

6.1.3.2 Relative Positioning of Air Inlet Port and Chamber Inlet Port

[0419] In addition to preventing spilled water from reaching air inlet port 5334, it may be desirable to return at least a portion of the trapped water to the reservoir 5110 when the humidifier 5000 is returned to an intended working orientation.

[0420] As shown in FIGS. 5G to 5I, the chamber inlet port 5314 is positioned relative to the air inlet port 5334 such that when the humidifier is in an intended working orientation, a lowest point of the chamber inlet port 5314 is inferior to a lowest point of the air inlet port 5334 - i.e. there is a vertical separation 5382 between these points.

[0421] Referring to FIG. 5J, when the humidifier 5000 is tipped such that water is displaced through chamber inlet port 5314, the liquid trap 5380 can retain a volume of water below a level between the chamber inlet port 5314 and air inlet port 5334. In the example shown in FIG. 5J, the liquid trap is configured to accommodate a tip angle of substantially 20 degrees from level. It will be appreciated that the volume of water to be retained will be somewhat dependent on the total capacity and configuration of the humidifier 5000, but in this example the liquid trap 5380 may be configured to capture a volume of about 40 to 70 ml of water, more particularly about 50 ml of water. When the humidifier 5000 is returned to its intended working orientation (i.e. a substantially level orientation), as shown in FIG. 5K, the vertical separation 5382 ensures that at least some water may drain from the liquid trap 5380 back through the chamber inlet port 5314.

[0422] While the liquid trap 5380 may retain a small volume of the spilled water, as shown in FIG. 5K, this will be less than the total capacity of the liquid trap 5380. It is envisaged that this relatively small volume of water may be readily evaporated by airflow through the liquid trap 5380 in use.

[0423] In examples, as shown in FIG. 5I a centre of the chamber inlet port 5314 is laterally offset from a centre of the air inlet port 5334. This offset may assist in accommodation of other components of the humidifier 5000 or RPT device 4000. This offset may also be used to reduce the likelihood of spilling through the air inlet port 5334 when the humidifier 5000 is tipped in certain directions, based on expected orientation in use relative to environmental features such as the edge of a bedside table from which the device may be knocked accidentally.

6.1.3.3 Superior and Lateral Portions

[0424] According to one aspect of the present technology, as shown in FIG. 5L, in examples the liquid trap 5380 comprises a superior portion 5384 above the reservoir 5110 (not shown in FIG. 5L) when the humidifier 5000 is in an in-use orientation. This superior portion 5384 provides additional volume to the liquid trap 5380 for capture of water being spilled from the reservoir 5110 in the event of knocking or tipping of the humidifier 5000, particularly an event that results in the humidifier being tipped upside down from its intended orientation in use. In this example, it is envisaged that the liquid trap 5380 may accommodate a volume of about 60 ml of spilled water.

[0425] In examples, the chassis 5310 comprises an inner chassis wall portion 5320, providing at least a portion of a supporting structure for the reservoir 5110 (or the reservoir itself in certain examples). In the example of FIG. 5L, a superior portion of the chassis peripheral wall 5316 extends towards the end cap 5330 from a position on the inner chassis wall portion 5320 away from the vertical chassis wall 5312. The volume between the superior portion of the chassis peripheral wall 5316 and the inner chassis wall portion 5320 provides the superior portion 5384 of the liquid trap 5380.

[0426] In examples, the superior portion 5384 is configured such that liquid drains from the superior portion 5384 into an inferior portion of the liquid trap 5380 (for example, where the chamber inlet port 5314 opens into the liquid trap 5380), when the humidifier 5000 is returned to its intended working orientation (i.e. a substantially level orientation). Draining of the liquid reduces the likelihood of pooling of the liquid and bacteria contamination. In examples, a superior facing surface 5322 of the inner chassis wall portion 5320 is inclined to encourage draining -as shown in FIG. 5L. In alternative examples, the superior facing surface 5322 may comprise one or more channels through which draining occurs.

[0427] According to one aspect of the present technology, as shown in FIG. 5M, in examples the liquid trap 5380 comprises a lateral portion 5386. The lateral portion 5386 extends laterally from the portion of the liquid trap 5380 surrounding the chamber inlet port 5314 (i.e. to the side of the chamber inlet port 5314 and/or the air inlet port 5334). The lateral portion 5386 provides additional volume to the liquid trap 5380 for capture of water being spilled from the reservoir 5110 in the event of knocking or tipping of the humidifier 5000. The height of the lateral portion 5386 is less than the greatest height of the liquid trap 5380, where height is the dimension in the superior-inferior direction when the humidifier 5000 is in an in-use orientation. In examples, the lateral portion 5386 may extend from the superior portion 5384 shown in FIG. 5L.

[0428] In examples, the lateral portion 5386 is configured such that liquid drains into an inferior portion of the liquid trap 5380 (for example, where the chamber inlet port 5314 opens into the liquid trap 5380) when the humidifier 5000 is returned to its intended working orientation (i.e. a substantially level orientation). In examples, a superior facing surface of the lateral portion 5386 may be inclined, and/or include channels, to encourage draining.

[0429] In the example shown in FIG. 5L, the end cap 5330 includes a locating feature 5344 at the air inlet port 5334. In this example, the locating feature 5344 is a recess configured to receive a complementary locating feature of a connector (not shown) inserted into the air inlet port 5334, for example to connect the humidifier 5000 to a flow generator or RPT device.

[0430] In the example shown in FIG. 5L and FIG. 5M, the resilient seal 5360 does not cover the entirety of the inner surfaces of the end cap 5330 forming the liquid trap 5380. In this example the liquid trap portion 5362 of the seal 5360 is provided on the rim of the inner peripheral wall 5340 to seal against radially inwardly facing surfaces of the chassis peripheral wall 5340, and the air inlet port portion 5366 of the seal 5360 is provided at the air inlet port 5334, but the majority of the surface area of the liquid trap 5380 is provided by the walls of the end cap 5330. In this example, the liquid trap portion 5362 and the air inlet port portion 5366 are connected by one or more seal runner portions 5374 to allow for manufacture of the seal 5360 as one part. It should be appreciated that other seal features of the end cap 5330 (for example, peripheral seal portion 5372) may also be connected to one or more of the liquid trap portion 5362 and the air inlet port portion 5366.

6.1.3.4 Inverted Receptacle

[0431] According to one aspect of the present technology, as shown in FIG. 6A, an inverted receptacle 5600 may be provided to a superior portion of the chamber inlet port 5314 when the humidifier 5000 is in an intended working orientation. The inverted receptacle 5600 comprises a closed end 5602 and an open end 5604, with a curved receptacle wall 5606 to provide a semicylindrical form. The open end 5604 intersects and aligns with the chamber inlet port 5314.

[0432] As shown in FIG. 6B, in this example the inverted receptacle extends from the chassis 5310 towards the end cap 5330. In the event of knocking or tipping of the humidifier 5000, particularly an event that results in the humidifier being tipped upside down from its intended orientation in use (i.e. inverted), water spilling through the chamber inlet port 5314 may be captured within the receptacle 5600, or at least partially diverted into the liquid trap 5380 rather than spilling directly into the air inlet port 5334.

[0433] In examples, as shown in FIG. 6C and FIG. 6D the inverted receptacle 5600 comprises at least one drain hole 5608. In the example illustrated the drain hole 5608 is provided in a superior facing surface of the receptacle wall 5606 (noting that FIG. 6C and FIG. 6D show the receptacle when the humidifier 5000 has been inverted from an intended working orientation), at the apex of the curve. In use liquid may drain through the drain hole 5608 into the liquid trap 5384, and reduce the likelihood of spilling over the closed end of the receptacle 5600 towards the air inlet 5334.

6.1.3.5 Interior Trap Wall

[0434] According to one aspect of the present technology, as shown in FIG. 7A and FIG. 7B, the humidifier 5000 comprises an interior trap wall 5700 surrounding the air inlet port 5334, and extending from the end cap 5330 (more particularly the main cap wall 5332) towards the chamber inlet port 5314. The volume surrounding the interior trap wall 5700 forms a catchment of the liquid trap when the humidifier 5000 is tipped on, or at least towards, its end.

[0435] In examples, as shown in FIG. 7C, an inverted receptacle 5600 extends from the chassis 5310 towards the interior trap wall 5700. In the example illustrated the inverted receptacle 5600 extends to be proximal to, and contact, the interior trap wall 5700. In doing so, in the event of liquid being spilled through the chamber inlet port 5314 when the humidifier 5000 is inverted, spilling of the liquid directly from the receptacle 5600 into the air inlet port 5334 is discouraged.

6.1.3.6 Baffle Portions

[0436] According to one aspect of the present technology the humidifier 5000 comprises a baffle portion positioned between the air inlet port and the chamber inlet port, configured to direct liquid flowing from the chamber inlet port 5314 in a radial direction.

[0437] In examples, as shown in FIG. 8A and FIG. 8B, a baffle portion 5800 may form part of an inverted receptacle 5600. The closed end 5602 may include a baffle extension 5802 extending the area of the closed end 5602, shaped to block a portion of the air inlet port 5334 (as shown in FIG. 8B). The inverted receptacle 5600 further comprises a radially extending baffle portion 5804, which functions to direct liquid being spilled from the chamber inlet port 5314 away from the air inlet port 5334.

[0438] FIG. 8C shows an alternative example in which the closed end 5602 of inverted receptacle 5600 comprises a baffle extension 5802 forming a complete disc. FIG. 8D illustrates an alternative baffle portion 5800 comprising a flat upright baffle member 5806 supported by a plurality of baffle support members in the form of baffle legs 5808. The baffle legs 5808 extend from the chassis 5310, with gaps between the baffle legs 5808 and the baffle member 5806 permitting the flow of air therethrough.

6.1.3.7 Liquid Trap Partition

[0439] According to one aspect of the present technology the humidifier 5000 comprises at least one liquid trap partition 5850 providing a plurality of liquid trap catchments within the liquid trap 5380.

[0440] In examples, as shown in FIG. 9, the liquid trap partition 5850 comprises a first portion 5852 and a second portion 5854. In examples the first portion 5852 and the second portion 5854 are separate parts, while in alternative examples the first portion 5852 and the second portion 5854 may be a unitary part. The first portion 5852 comprises an upright intermediary wall 5856, and a dividing wall 5858 extending from the upright intermediary wall 5856 into the superior portion 5384 above the reservoir 5110 (noting that FIG. 9 shows the humidifier 5000 in an inverted orientation). A partition wall 5860 extends from the upright intermediary wall towards the chassis 5310, wherein a first gap 5862 is provided between the chamber inlet port 5314 and the partition wall 5860.

[0441] When the humidifier 5000 is in an inverted orientation, a first liquid trap catchment 5870 is provided inferior to the chamber inlet port 5314 - through the first gap 5862 and bounded by the upright intermediary wall 5856, the partition wall 5860, and dividing wall 5858. A second liquid trap catchment 5872 is provided inferior to the first liquid trap catchment 5870, with liquid running from the first liquid trap catchment 5870 along the dividing wall 5858 and through a second gap 5864 at a free end of the dividing wall 5858.

[0442] In examples the second portion 5854 forms an interior trap wall extending from the end cap 5330 towards the chamber inlet port 5314. The second portion 5854 surrounds the air inlet port 5334 to define a third liquid trap catchment 5874 (i.e. the volume around the exterior of the second portion 5854).

6.1.3.8 Moveable Barrier

[0443] According to one aspect of the present technology, as shown in FIG. 10, the humidifier 5000 comprises a moveable barrier 5900 configured to selectively block the air inlet port 5334 when the humidifier 5000 is inverted from an intended working orientation. For completeness, it is noted that in examples a moveable barrier 5900 may be used to block the chamber inlet port 5314 - instead of, or in addition to, use of a moveable barrier 5900 to selectively block the air inlet port 5334.

[0444] The moveable barrier 5900 is configured to move between a stored position 5910 away from the air inlet port 5334 when the humidifier is in an intended working orientation, and a closed position 5912 blocking the air inlet port 5334 when the humidifier 5000 is in an inverted orientation.

[0445] In the example shown, the moveable barrier 5900 comprises a barrier body 5902 in the form of a flat plate, having a pivot 5904 (for example a pin or protrusion) positioned inferior to the air inlet port 5334. As the humidifier 5000 is tipped off-axis, gravity causes the barrier body 5902 to pivot about the pivot 5904 and fall to cover the air inlet port 5334. As the humidifier 5000 is returned to its intended working orientation, gravity causes the barrier body 5902 to pivot about the pivot 5904 and fall to away from the air inlet port 5334.

[0446] In an alternative example, the moveable barrier 5900 may comprise a hinge, such that the barrier body 5902 functions as a hinged lid. In an alternative example the moveable barrier 5900 may be configured to slide relative to the air inlet port 5334, for example sliding on one or more tracks.

6.1.3.9 Secondary Closure Element

[0447] According to one aspect of the present technology, as shown in FIG. 11, the end cap 5330 may be configured to interact with a secondary closure element 5950 to provide the liquid trap 5380. For example, the secondary closure element 5950 may be a component of the RPT device 4000. In such an example, the secondary closure element 5950 may comprise outlet 4130 which acts as the air inlet port 5334.

[0448] In alternative examples, the secondary closure element 5950 may function as an interface between the RPT device 4000 and the humidifier 5000 - e.g. pneumatically connecting to the outlet 4000 and interfacing with the end cap 5330 to provide the air inlet port 5334.

[0449] It should be appreciated that, in examples, one or more features described herein as being part of the end cap 5330 may be embodied in the secondary closure element 5950, and operate cooperatively with the end cap 5330 to achieve the functionality described.

6.2 Glossary

[0450] For the purposes of the present technology disclosure, in certain forms of the present technology, one or more of the following definitions may apply. In other forms of the present technology, alternative definitions may apply.

6.2.1 General

[0451] Air: In certain forms of the present technology, air may be taken to mean atmospheric air, and in other forms of the present technology air may be taken to mean some other combination of breathable gases, e.g. atmospheric air enriched with oxygen.

[0452] Ambient: In certain forms of the present technology, the term ambient will be taken to mean (i) external of the treatment system or patient, and (ii) immediately surrounding the treatment system or patient.

[0453] For example, ambient humidity with respect to a humidifier may be the humidity of air immediately surrounding the humidifier, e.g. the humidity in the room where a patient is sleeping. Such ambient humidity may be different to the humidity outside the room where a patient is sleeping.

[0454] In another example, ambient pressure may be the pressure immediately surrounding or external to the body.

[0455] In certain forms, ambient (e.g., acoustic) noise may be considered to be the background noise level in the room where a patient is located, other than for example, noise generated by an RPT device or emanating from a mask or patient interface. Ambient noise may be generated by sources outside the room.

[0456] Automatic Positive Airway Pressure (APAP) therapy: CPAP therapy in which the treatment pressure is automatically adjustable, e.g. from breath to breath, between minimum and maximum limits, depending on the presence or absence of indications of SDB events.

[0457] Continuous Positive Airway Pressure (CPAP) therapy: Respiratory pressure therapy in which the treatment pressure is approximately constant through a respiratory cycle of a patient. In some forms, the pressure at the entrance to the airways will be slightly higher during exhalation, and slightly lower during inhalation. In some forms, the pressure will vary between different respiratory cycles of the patient, for example, being increased in response to detection of indications of partial upper airway obstruction, and decreased in the absence of indications of partial upper airway obstruction.

[0458] Flow rate: The volume (or mass) of air delivered per unit time. Flow rate may refer to an instantaneous quantity. In some cases, a reference to flow rate will be a reference to a scalar quantity, namely a quantity having magnitude only. In other cases, a reference to flow rate will be a reference to a vector quantity, namely a quantity having both magnitude and direction. Flow rate may be given the symbol Q. ‘Flow rate’ is sometimes shortened to simply ‘flow’ or ‘airflow’.

[0459] In the example of patient respiration, a flow rate may be nominally positive for the inspiratory portion of a breathing cycle of a patient, and hence negative for the expiratory portion of the breathing cycle of a patient. Device flow rate, Qd, is the flow rate of air leaving the RPT device. Total flow rate, Qt, is the flow rate of air and any supplementary gas reaching the patient interface via the air circuit. Vent flow rate, Qv, is the flow rate of air leaving a vent to allow washout of exhaled gases. Leak flow rate, Ql, is the flow rate of leak from a patient interface system or elsewhere. Respiratory flow rate, Qr, is the flow rate of air that is received into the patient’s respiratory system.

[0460] Flow therapy: Respiratory therapy comprising the delivery of a flow of air to an entrance to the airways at a controlled flow rate referred to as the treatment flow rate that is typically positive throughout the patient’s breathing cycle.

[0461] Humidifier: The word humidifier will be taken to mean a humidifying apparatus constructed and arranged, or configured with a physical structure to be capable of providing a therapeutically beneficial amount of water (H.sub.2O) vapour to a flow of air to ameliorate a medical respiratory condition of a patient.

[0462] Leak: The word leak will be taken to be an unintended flow of air. In one example, leak may occur as the result of an incomplete seal between a mask and a patient’s face. In another example leak may occur in a swivel elbow to the ambient.

[0463] Noise, conducted (acoustic): Conducted noise in the present document refers to noise which is carried to the patient by the pneumatic path, such as the air circuit and the patient interface as well as the air therein. In one form, conducted noise may be quantified by measuring sound pressure levels at the end of an air circuit.

[0464] Noise, radiated (acoustic): Radiated noise in the present document refers to noise which is carried to the patient by the ambient air. In one form, radiated noise may be quantified by measuring sound power/pressure levels of the object in question according to ISO 3744.

[0465] Noise, vent (acoustic): Vent noise in the present document refers to noise which is generated by the flow of air through any vents such as vent holes of the patient interface.

[0466] Patient: A person, whether or not they are suffering from a respiratory condition.

[0467] Pressure: Force per unit area. Pressure may be expressed in a range of units, including cmH.sub.2O, g-f/cm.sup.2 and hectopascal. 1 cmH.sub.2O is equal to 1 g-f/cm.sup.2 and is approximately 0.98 hectopascal (1 hectopascal = 100 Pa = 100 N/m.sup.2 = 1 millibar -0.001 atm). In this specification, unless otherwise stated, pressure is given in units of cmH.sub.2O.

[0468] The pressure in the patient interface is given the symbol Pm, while the treatment pressure, which represents a target value to be achieved by the interface pressure Pm at the current instant of time, is given the symbol Pt.

[0469] Respiratory Pressure Therapy (RPT): The application of a supply of air to an entrance to the airways at a treatment pressure that is typically positive with respect to atmosphere.

[0470] Ventilator: A mechanical device that provides pressure support to a patient to perform some or all of the work of breathing.

6.2.1.1 Materials

[0471] Silicone or Silicone Elastomer: A synthetic rubber. In this specification, a reference to silicone is a reference to liquid silicone rubber (LSR) or a compression moulded silicone rubber (CMSR). One form of commercially available LSR is SILASTIC (included in the range of products sold under this trademark), manufactured by Dow Corning. Another manufacturer of LSR is Wacker. Unless otherwise specified to the contrary, an exemplary form of LSR has a Shore A (or Type A) indentation hardness in the range of about 35 to about 45 as measured using ASTM D2240.

[0472] Polycarbonate: a thermoplastic polymer of Bisphenol-A Carbonate.

6.2.1.2 Mechanical Properties

[0473] Resilience: Ability of a material to absorb energy when deformed elastically and to release the energy upon unloading.

[0474] Resilient: Will release substantially all of the energy when unloaded. Includes e.g. certain silicones, and thermoplastic elastomers.

[0475] Hardness: The ability of a material per se to resist deformation (e.g. described by a Young’s Modulus, or an indentation hardness scale measured on a standardised sample size). [0476] ‘Soft’ materials may include silicone or thermo-plastic elastomer (TPE), and may, e.g. readily deform under finger pressure. [0477] ‘Hard’ materials may include polycarbonate, polypropylene, steel or aluminium, and may not e.g. readily deform under finger pressure.

[0478] Stiffness (or rigidity) of a structure or component: The ability of the structure or component to resist deformation in response to an applied load. The load may be a force or a moment, e.g. compression, tension, bending or torsion. The structure or component may offer different resistances in different directions. The inverse of stiffness is flexibility.

[0479] Floppy structure or component: A structure or component that will change shape, e.g. bend, when caused to support its own weight, within a relatively short period of time such as 1 second.

[0480] Rigid structure or component: A structure or component that will not substantially change shape when subject to the loads typically encountered in use. An example of such a use may be setting up and maintaining a patient interface in sealing relationship with an entrance to a patient’s airways, e.g. at a load of approximately 20 to 30 cmH.sub.2O pressure.

[0481] As an example, an I-beam may comprise a different bending stiffness (resistance to a bending load) in a first direction in comparison to a second, orthogonal direction. In another example, a structure or component may be floppy in a first direction and rigid in a second direction.

6.2.2 Respiratory Cycle

[0482] Apnea: According to some definitions, an apnea is said to have occurred when flow falls below a predetermined threshold for a duration, e.g. 10 seconds. An obstructive apnea will be said to have occurred when, despite patient effort, some obstruction of the airway does not allow air to flow. A central apnea will be said to have occurred when an apnea is detected that is due to a reduction in breathing effort, or the absence of breathing effort, despite the airway being patent. A mixed apnea occurs when a reduction or absence of breathing effort coincides with an obstructed airway.

[0483] Breathing rate: The rate of spontaneous respiration of a patient, usually measured in breaths per minute.

[0484] Duty cycle: The ratio of inhalation time, Ti to total breath time, Ttot.

[0485] Effort (breathing): The work done by a spontaneously breathing person attempting to breathe.

[0486] Expiratory portion of a breathing cycle: The period from the start of expiratory flow to the start of inspiratory flow.

[0487] Flow limitation: Flow limitation will be taken to be the state of affairs in a patient’s respiration where an increase in effort by the patient does not give rise to a corresponding increase in flow. Where flow limitation occurs during an inspiratory portion of the breathing cycle it may be described as inspiratory flow limitation. Where flow limitation occurs during an expiratory portion of the breathing cycle it may be described as expiratory flow limitation.

[0488] Types of flow limited inspiratory waveforms: [0489] (i) Flattened: Having a rise followed by a relatively flat portion, followed by a fall. [0490] (ii) M-shaped: Having two local peaks, one at the leading edge, and one at the trailing edge, and a relatively flat portion between the two peaks. [0491] (iii) Chair-shaped: Having a single local peak, the peak being at the leading edge, followed by a relatively flat portion. [0492] (iv) Reverse-chair shaped: Having a relatively flat portion followed by single local peak, the peak being at the trailing edge.

[0493] Hypopnea: According to some definitions, a hypopnea is taken to be a reduction in flow, but not a cessation of flow. In one form, a hypopnea may be said to have occurred when there is a reduction in flow below a threshold rate for a duration. A central hypopnea will be said to have occurred when a hypopnea is detected that is due to a reduction in breathing effort. In one form in adults, either of the following may be regarded as being hypopneas: [0494] (i) a 30% reduction in patient breathing for at least 10 seconds plus an associated 4% desaturation; or [0495] (ii) a reduction in patient breathing (but less than 50%) for at least 10 seconds, with an associated desaturation of at least 3% or an arousal.

[0496] Hyperpnea: An increase in flow to a level higher than normal.

[0497] Inspiratory portion of a breathing cycle: The period from the start of inspiratory flow to the start of expiratory flow will be taken to be the inspiratory portion of a breathing cycle.

[0498] Patency (airway): The degree of the airway being open, or the extent to which the airway is open. A patent airway is open. Airway patency may be quantified, for example with a value of one (1) being patent, and a value of zero (0), being closed (obstructed).

[0499] Positive End-Expiratory Pressure (PEEP): The pressure above atmosphere in the lungs that exists at the end of expiration.

[0500] Peak flow rate (Qpeak): The maximum value of flow rate during the inspiratory portion of the respiratory flow waveform.

[0501] Respiratory flow rate, patient airflow rate, respiratory airflow rate (Qr): These terms may be understood to refer to the RPT device’s estimate of respiratory flow rate, as opposed to “true respiratory flow rate” or “true respiratory flow rate”, which is the actual respiratory flow rate experienced by the patient, usually expressed in litres per minute.

[0502] Tidal volume (Vt): The volume of air inhaled or exhaled during normal breathing, when extra effort is not applied. In principle the inspiratory volume Vi (the volume of air inhaled) is equal to the expiratory volume Ve (the volume of air exhaled), and therefore a single tidal volume Vt may be defined as equal to either quantity. In practice the tidal volume Vt is estimated as some combination, e.g. the mean, of the inspiratory volume Vi and the expiratory volume Ve.

[0503] (inhalation) Time (Ti): The duration of the inspiratory portion of the respiratory flow rate waveform.

[0504] (exhalation) Time (Te): The duration of the expiratory portion of the respiratory flow rate waveform.

[0505] (total) Time (Ttot): The total duration between the start of one inspiratory portion of a respiratory flow rate waveform and the start of the following inspiratory portion of the respiratory flow rate waveform.

[0506] Typical recent ventilation: The value of ventilation around which recent values of ventilation Vent over some predetermined timescale tend to cluster, that is, a measure of the central tendency of the recent values of ventilation.

[0507] Upper airway obstruction (UAO): includes both partial and total upper airway obstruction. This may be associated with a state of flow limitation, in which the flow rate increases only slightly or may even decrease as the pressure difference across the upper airway increases (Starling resistor behaviour).

[0508] Ventilation (Vent): A measure of a rate of gas being exchanged by the patient’s respiratory system. Measures of ventilation may include one or both of inspiratory and expiratory flow, per unit time. When expressed as a volume per minute, this quantity is often referred to as “minute ventilation”. Minute ventilation is sometimes given simply as a volume, understood to be the volume per minute.

6.2.3 Ventilation

[0509] Adaptive Servo- Ventilator (ASV): A servo-ventilator that has a changeable, rather than fixed target ventilation. The changeable target ventilation may be learned from some characteristic of the patient, for example, a respiratory characteristic of the patient.

[0510] Backup rate: A parameter of a ventilator that establishes the minimum breathing rate (typically in number of breaths per minute) that the ventilator will deliver to the patient, if not triggered by spontaneous respiratory effort.

[0511] Cycled: The termination of a ventilator’s inspiratory phase. When a ventilator delivers a breath to a spontaneously breathing patient, at the end of the inspiratory portion of the breathing cycle, the ventilator is said to be cycled to stop delivering the breath.

[0512] Expiratory positive airway pressure (EPAP): a base pressure, to which a pressure varying within the breath is added to produce the desired interface pressure which the ventilator will attempt to achieve at a given time.

[0513] End expiratory pressure (EEP): Desired interface pressure which the ventilator will attempt to achieve at the end of the expiratory portion of the breath. If the pressure waveform template Π(Φ) is zero-valued at the end of expiration, i.e. Π(Φ) = 0 when Φ = 1, the EEP is equal to the EPAP.

[0514] Inspiratory positive airway pressure (IPAP): Maximum desired interface pressure which the ventilator will attempt to achieve during the inspiratory portion of the breath.

[0515] Pressure support: A number that is indicative of the increase in pressure during ventilator inspiration over that during ventilator expiration, and generally means the difference in pressure between the maximum value during inspiration and the base pressure (e.g., PS = IPAP - EPAP). In some contexts, pressure support means the difference which the ventilator aims to achieve, rather than what it actually achieves.

[0516] Servo-ventilator: A ventilator that measures patient ventilation, has a target ventilation, and which adjusts the level of pressure support to bring the patient ventilation towards the target ventilation.

[0517] Spontaneous/Timed (S/T): A mode of a ventilator or other device that attempts to detect the initiation of a breath of a spontaneously breathing patient. If, however, the device is unable to detect a breath within a predetermined period of time, the device will automatically initiate delivery of the breath.

[0518] Swing: Equivalent term to pressure support.

[0519] Triggered: When a ventilator delivers a breath of air to a spontaneously breathing patient, it is said to be triggered to do so at the initiation of the respiratory portion of the breathing cycle by the patient’s efforts.

6.2.4 Anatomy

6.2.4.1 Anatomy of the Face

[0520] Ala: the external outer wall or “wing” of each nostril (plural: alar)

[0521] Alare: The most lateral point on the nasal ala.

[0522] Alar curvature (or alar crest) point: The most posterior point in the curved base line of each ala, found in the crease formed by the union of the ala with the cheek.

[0523] Auricle: The whole external visible part of the ear.

[0524] (nose) Bony framework: The bony framework of the nose comprises the nasal bones, the frontal process of the maxillae and the nasal part of the frontal bone.

[0525] (nose) Cartilaginous framework: The cartilaginous framework of the nose comprises the septal, lateral, major and minor cartilages.

[0526] Columella: the strip of skin that separates the nares and which runs from the pronasale to the upper lip.

[0527] Columella angle: The angle between the line drawn through the midpoint of the nostril aperture and a line drawn perpendicular to the Frankfort horizontal while intersecting subnasale.

[0528] Frankfort horizontal plane: A line extending from the most inferior point of the orbital margin to the left tragion. The tragion is the deepest point in the notch superior to the tragus of the auricle.

[0529] Glabella: Located on the soft tissue, the most prominent point in the midsagittal plane of the forehead.

[0530] Lateral nasal cartilage: A generally triangular plate of cartilage. Its superior margin is attached to the nasal bone and frontal process of the maxilla, and its inferior margin is connected to the greater alar cartilage.

[0531] Greater alar cartilage: A plate of cartilage lying below the lateral nasal cartilage. It is curved around the anterior part of the naris. Its posterior end is connected to the frontal process of the maxilla by a tough fibrous membrane containing three or four minor cartilages of the ala.

[0532] Nares (Nostrils): Approximately ellipsoidal apertures forming the entrance to the nasal cavity. The singular form of nares is naris (nostril). The nares are separated by the nasal septum.

[0533] Naso-labial sulcus or Naso-labial fold: The skin fold or groove that runs from each side of the nose to the corners of the mouth, separating the cheeks from the upper lip.

[0534] Naso-labial angle: The angle between the columella and the upper lip, while intersecting subnasale.

[0535] Otobasion inferior: The lowest point of attachment of the auricle to the skin of the face.

[0536] Otobasion superior: The highest point of attachment of the auricle to the skin of the face.

[0537] Pronasale: the most protruded point or tip of the nose, which can be identified in lateral view of the rest of the portion of the head.

[0538] Philtrum: the midline groove that runs from lower border of the nasal septum to the top of the lip in the upper lip region.

[0539] Pogonion: Located on the soft tissue, the most anterior midpoint of the chin.

[0540] Ridge (nasal): The nasal ridge is the midline prominence of the nose, extending from the Sellion to the Pronasale.

[0541] Sagittal plane: A vertical plane that passes from anterior (front) to posterior (rear). The midsagittal plane is a sagittal plane that divides the body into right and left halves.

[0542] Sellion: Located on the soft tissue, the most concave point overlying the area of the frontonasal suture.

[0543] Septal cartilage (nasal): The nasal septal cartilage forms part of the septum and divides the front part of the nasal cavity.

[0544] Subalare: The point at the lower margin of the alar base, where the alar base joins with the skin of the superior (upper) lip.

[0545] Subnasal point: Located on the soft tissue, the point at which the columella merges with the upper lip in the midsagittal plane.

[0546] Supramenton: The point of greatest concavity in the midline of the lower lip between labrale inferius and soft tissue pogonion

6.2.4.2 Anatomy of the Skull

[0547] Frontal bone: The frontal bone includes a large vertical portion, the squama frontalis, corresponding to the region known as the forehead.

[0548] Mandible: The mandible forms the lower jaw. The mental protuberance is the bony protuberance of the jaw that forms the chin.

[0549] Maxilla: The maxilla forms the upper jaw and is located above the mandible and below the orbits. The frontal process of the maxilla projects upwards by the side of the nose, and forms part of its lateral boundary.

[0550] Nasal bones: The nasal bones are two small oblong bones, varying in size and form in different individuals; they are placed side by side at the middle and upper part of the face, and form, by their junction, the “bridge” of the nose.

[0551] Nasion: The intersection of the frontal bone and the two nasal bones, a depressed area directly between the eyes and superior to the bridge of the nose.

[0552] Occipital bone: The occipital bone is situated at the back and lower part of the cranium. It includes an oval aperture, the foramen magnum, through which the cranial cavity communicates with the vertebral canal. The curved plate behind the foramen magnum is the squama occipitalis.

[0553] Orbit: The bony cavity in the skull to contain the eyeball.

[0554] Parietal bones: The parietal bones are the bones that, when joined together, form the roof and sides of the cranium.

[0555] Temporal bones: The temporal bones are situated on the bases and sides of the skull, and support that part of the face known as the temple.

[0556] Zygomatic bones: The face includes two zygomatic bones, located in the upper and lateral parts of the face and forming the prominence of the cheek.

6.2.4.3 Anatomy of the Respiratory System

[0557] Diaphragm: A sheet of muscle that extends across the bottom of the rib cage. The diaphragm separates the thoracic cavity, containing the heart, lungs and ribs, from the abdominal cavity. As the diaphragm contracts the volume of the thoracic cavity increases and air is drawn into the lungs.

[0558] Larynx: The larynx, or voice box houses the vocal folds and connects the inferior part of the pharynx (hypopharynx) with the trachea.

[0559] Lungs: The organs of respiration in humans. The conducting zone of the lungs contains the trachea, the bronchi, the bronchioles, and the terminal bronchioles. The respiratory zone contains the respiratory bronchioles, the alveolar ducts, and the alveoli.

[0560] Nasal cavity: The nasal cavity (or nasal fossa) is a large air filled space above and behind the nose in the middle of the face. The nasal cavity is divided in two by a vertical fin called the nasal septum. On the sides of the nasal cavity are three horizontal outgrowths called nasal conchae (singular “concha”) or turbinates. To the front of the nasal cavity is the nose, while the back blends, via the choanae, into the nasopharynx.

[0561] Pharynx: The part of the throat situated immediately inferior to (below) the nasal cavity, and superior to the oesophagus and larynx. The pharynx is conventionally divided into three sections: the nasopharynx (epipharynx) (the nasal part of the pharynx), the oropharynx (mesopharynx) (the oral part of the pharynx), and the laryngopharynx (hypopharynx).

6.2.5 Patient Interface

[0562] Anti-asphyxia valve (AAV): The component or sub-assembly of a mask system that, by opening to atmosphere in a failsafe manner, reduces the risk of excessive CO.sub.2 rebreathing by a patient.

[0563] Elbow: An elbow is an example of a structure that directs an axis of flow of air travelling therethrough to change direction through an angle. In one form, the angle may be approximately 90 degrees. In another form, the angle may be more, or less than 90 degrees. The elbow may have an approximately circular cross-section. In another form the elbow may have an oval or a rectangular cross-section. In certain forms an elbow may be rotatable with respect to a mating component, e.g. about 360 degrees. In certain forms an elbow may be removable from a mating component, e.g. via a snap connection. In certain forms, an elbow may be assembled to a mating component via a one-time snap during manufacture, but not removable by a patient.

[0564] Frame: Frame will be taken to mean a mask structure that bears the load of tension between two or more points of connection with a headgear. A mask frame may be a non-airtight load bearing structure in the mask. However, some forms of mask frame may also be air-tight.

[0565] Headgear: Headgear will be taken to mean a form of positioning and stabilizing structure designed for use on a head. For example, the headgear may comprise a collection of one or more struts, ties and stiffeners configured to locate and retain a patient interface in position on a patient’s face for delivery of respiratory therapy. Some ties are formed of a soft, flexible, elastic material such as a laminated composite of foam and fabric.

[0566] Membrane: Membrane will be taken to mean a typically thin element that has, preferably, substantially no resistance to bending, but has resistance to being stretched.

[0567] Plenum chamber: a mask plenum chamber will be taken to mean a portion of a patient interface having walls at least partially enclosing a volume of space, the volume having air therein pressurised above atmospheric pressure in use. A shell may form part of the walls of a mask plenum chamber.

[0568] Seal: May be a noun form (“a seal”) which refers to a structure, or a verb form (“to seal”) which refers to the effect. Two elements may be constructed and/or arranged to ‘seal’ or to effect ‘sealing’ therebetween without requiring a separate ‘seal’ element per se.

[0569] Shell: A shell will be taken to mean a curved, relatively thin structure having bending, tensile and compressive stiffness. For example, a curved structural wall of a mask may be a shell. In some forms, a shell may be faceted. In some forms a shell may be airtight. In some forms a shell may not be airtight.

[0570] Stiffener: A stiffener will be taken to mean a structural component designed to increase the bending resistance of another component in at least one direction.

[0571] Strut: A strut will be taken to be a structural component designed to increase the compression resistance of another component in at least one direction.

[0572] Swivel (noun): A subassembly of components configured to rotate about a common axis, preferably independently, preferably under low torque. In one form, the swivel may be constructed to rotate through an angle of at least 360 degrees. In another form, the swivel may be constructed to rotate through an angle less than 360 degrees. When used in the context of an air delivery conduit, the sub-assembly of components preferably comprises a matched pair of cylindrical conduits. There may be little or no leak flow of air from the swivel in use.

[0573] Tie (noun): A structure designed to resist tension.

[0574] Vent: (noun): A structure that allows a flow of air from an interior of the mask, or conduit, to ambient air for clinically effective washout of exhaled gases. For example, a clinically effective washout may involve a flow rate of about 10 litres per minute to about 100 litres per minute, depending on the mask design and treatment pressure.

6.2.6 Shape of Structures

[0575] Products in accordance with the present technology may comprise one or more three-dimensional mechanical structures, for example a mask cushion or an impeller. The three-dimensional structures may be bounded by two-dimensional surfaces. These surfaces may be distinguished using a label to describe an associated surface orientation, location, function, or some other characteristic. For example, a structure may comprise one or more of an anterior surface, a posterior surface, an interior surface and an exterior surface. In another example, a seal-forming structure may comprise a face-contacting (e.g. outer) surface, and a separate non-face-contacting (e.g. underside or inner) surface. In another example, a structure may comprise a first surface and a second surface.

[0576] To facilitate describing the shape of the three-dimensional structures and the surfaces, we first consider a cross-section through a surface of the structure at a point, p. An outward normal vector at p points away from the surface. In some examples we describe the surface from the point of view of an imaginary small person standing upright on the surface.

6.2.6.1 Curvature in One Dimension

[0577] The curvature of a plane curve at p may be described as having a sign (e.g. positive, negative) and a magnitude (e.g. ⅟radius of a circle that just touches the curve at p).

[0578] Positive curvature: If the curve at p turns towards the outward normal, the curvature at that point will be taken to be positive (if the imaginary small person leaves the point p they must walk uphill). Such curves are often referred to as concave.

[0579] Zero curvature: If the curve at p is a straight line, the curvature will be taken to be zero (if the imaginary small person leaves the point p, they can walk on a level, neither up nor down).

[0580] Negative curvature: If the curve at p turns away from the outward normal, the curvature in that direction at that point will be taken to be negative (if the imaginary small person leaves the point p they must walk downhill). Such curves are often referred to as convex.

6.2.6.2 Curvature of Two Dimensional Surfaces

[0581] A description of the shape at a given point on a two-dimensional surface in accordance with the present technology may include multiple normal cross-sections. The multiple cross-sections may cut the surface in a plane that includes the outward normal (a “normal plane”), and each cross-section may be taken in a different direction. Each cross-section results in a plane curve with a corresponding curvature. The different curvatures at that point may have the same sign, or a different sign. Each of the curvatures at that point has a magnitude, e.g. relatively small.

[0582] Principal curvatures and directions: The directions of the normal planes where the curvature of the curve takes its maximum and minimum values are called the principal directions.

[0583] Region of a surface: A connected set of points on a surface. The set of points in a region may have similar characteristics, e.g. curvatures or signs.

[0584] Saddle region: A region where at each point, the principal curvatures have opposite signs, that is, one is positive, and the other is negative (depending on the direction to which the imaginary person turns, they may walk uphill or downhill).

[0585] Dome region: A region where at each point the principal curvatures have the same sign, e.g. both positive (a “concave dome”) or both negative (a “convex dome”).

[0586] Cylindrical region: A region where one principal curvature is zero (or, for example, zero within manufacturing tolerances) and the other principal curvature is non-zero.

[0587] Planar region: A region of a surface where both of the principal curvatures are zero (or, for example, zero within manufacturing tolerances).

[0588] Edge of a surface: A boundary or limit of a surface or region.

[0589] Path: In certain forms of the present technology, ‘path’ will be taken to mean a path in the mathematical - topological sense, e.g. a continuous space curve from f(0) to f(1) on a surface. In certain forms of the present technology, a ‘path’ may be described as a route or course, including e.g. a set of points on a surface. (The path for the imaginary person is where they walk on the surface, and is analogous to a garden path).

[0590] Path length: In certain forms of the present technology, ‘path length’ will be taken to mean the distance along the surface from f(0) to f(1), that is, the distance along the path on the surface. There may be more than one path between two points on a surface and such paths may have different path lengths. (The path length for the imaginary person would be the distance they have to walk on the surface along the path).

[0591] Straight-line distance: The straight-line distance is the distance between two points on a surface, but without regard to the surface. On planar regions, there would be a path on the surface having the same path length as the straight-line distance between two points on the surface. On non-planar surfaces, there may be no paths having the same path length as the straight-line distance between two points. (For the imaginary person, the straight-line distance would correspond to the distance ‘as the crow flies’.)

6.2.6.3 Space Curves

[0592] Space curves: Unlike a plane curve, a space curve does not necessarily lie in any particular plane. A space curve may be closed, that is, having no endpoints. A space curve may be considered to be a one-dimensional piece of three-dimensional space. An imaginary person walking on a strand of the DNA helix walks along a space curve. A typical human left ear comprises a helix, which is a left-hand helix. A typical human right ear comprises a helix, which is a right-hand helix. The edge of a structure, e.g. the edge of a membrane or impeller, may follow a space curve. In general, a space curve may be described by a curvature and a torsion at each point on the space curve. Torsion is a measure of how the curve turns out of a plane. Torsion has a sign and a magnitude. The torsion at a point on a space curve may be characterised with reference to the tangent, normal and binormal vectors at that point.

[0593] Tangent unit vector (or unit tangent vector): For each point on a curve, a vector at the point specifies a direction from that point, as well as a magnitude. A tangent unit vector is a unit vector pointing in the same direction as the curve at that point. If an imaginary person were flying along the curve and fell off her vehicle at a particular point, the direction of the tangent vector is the direction she would be travelling.

[0594] Unit normal vector: As the imaginary person moves along the curve, this tangent vector itself changes. The unit vector pointing in the same direction that the tangent vector is changing is called the unit principal normal vector. It is perpendicular to the tangent vector.

[0595] Binormal unit vector: The binormal unit vector is perpendicular to both the tangent vector and the principal normal vector. Its direction may be determined by a right-hand rule, or alternatively by a left-hand rule.

[0596] Osculating plane: The plane containing the unit tangent vector and the unit principal normal vector..

[0597] Torsion of a space curve: The torsion at a point of a space curve is the magnitude of the rate of change of the binormal unit vector at that point. It measures how much the curve deviates from the osculating plane. A space curve which lies in a plane has zero torsion. A space curve which deviates a relatively small amount from the osculating plane will have a relatively small magnitude of torsion (e.g. a gently sloping helical path). A space curve which deviates a relatively large amount from the osculating plane will have a relatively large magnitude of torsion (e.g. a steeply sloping helical path).

[0598] A space curve turning towards the direction of the right-hand binormal may be considered as having a right-hand positive torsion (e.g. a right-hand helix). A space curve turning away from the direction of the right-hand binormal may be considered as having a right-hand negative torsion (e.g. a left-hand helix).

[0599] Equivalently, and with reference to a left-hand rule, a space curve turning towards the direction of the left-hand binormal may be considered as having a left-hand positive torsion (e.g. a left-hand helix). Hence left-hand positive is equivalent to right-hand negative.

6.2.6.4 Holes

[0600] A surface may have a one-dimensional hole, e.g. a hole bounded by a plane curve or by a space curve. Thin structures (e.g. a membrane) with a hole, may be described as having a one-dimensional hole.

[0601] A structure may have a two-dimensional hole, e.g. a hole bounded by a surface. For example, an inflatable tyre has a two dimensional hole bounded by the interior surface of the tyre. In another example, a bladder with a cavity for air or gel could have a two-dimensional hole. In a yet another example, a conduit may comprise a one-dimension hole (e.g. at its entrance or at its exit), and a two-dimension hole bounded by the inside surface of the conduit.

6.3 Other Remarks

[0602] A portion of the disclosure of this patent document contains material which is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in Patent Office patent files or records, but otherwise reserves all copyright rights whatsoever.

[0603] Unless the context clearly dictates otherwise and where a range of values is provided, it is understood that each intervening value, to the tenth of the unit of the lower limit, between the upper and lower limit of that range, and any other stated or intervening value in that stated range is encompassed within the technology. The upper and lower limits of these intervening ranges, which may be independently included in the intervening ranges, are also encompassed within the technology, subject to any specifically excluded limit in the stated range. Where the stated range includes one or both of the limits, ranges excluding either or both of those included limits are also included in the technology.

[0604] Furthermore, where a value or values are stated herein as being implemented as part of the technology, it is understood that such values may be approximated, unless otherwise stated, and such values may be utilized to any suitable significant digit to the extent that a practical technical implementation may permit or require it.

[0605] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this technology belongs. Although any methods and materials similar or equivalent to those described herein can also be used in the practice or testing of the present technology, a limited number of the exemplary methods and materials are described herein.

[0606] When a particular material is identified as being used to construct a component, obvious alternative materials with similar properties may be used as a substitute. Furthermore, unless specified to the contrary, any and all components herein described are understood to be capable of being manufactured and, as such, may be manufactured together or separately.

[0607] It must be noted that as used herein and in the appended claims, the singular forms “a”, “an”, and “the” include their plural equivalents, unless the context clearly dictates otherwise.

[0608] All publications mentioned herein are incorporated herein by reference in their entirety to disclose and describe the methods and/or materials which are the subject of those publications. The publications discussed herein are provided solely for their disclosure prior to the filing date of the present application. Nothing herein is to be construed as an admission that the present technology is not entitled to antedate such publication by virtue of prior invention. Further, the dates of publication provided may be different from the actual publication dates, which may need to be independently confirmed.

[0609] The terms “comprises” and “comprising” should be interpreted as referring to elements, components, or steps in a non-exclusive manner, indicating that the referenced elements, components, or steps may be present, or utilized, or combined with other elements, components, or steps that are not expressly referenced.

[0610] The subject headings used in the detailed description are included only for the ease of reference of the reader and should not be used to limit the subject matter found throughout the disclosure or the claims. The subject headings should not be used in construing the scope of the claims or the claim limitations.

[0611] Although the technology herein has been described with reference to particular examples, it is to be understood that these examples are merely illustrative of the principles and applications of the technology. In some instances, the terminology and symbols may imply specific details that are not required to practice the technology. For example, although the terms “first” and “second” may be used, unless otherwise specified, they are not intended to indicate any order but may be utilised to distinguish between distinct elements. Furthermore, although process steps in the methodologies may be described or illustrated in an order, such an ordering is not required. Those skilled in the art will recognize that such ordering may be modified and/or aspects thereof may be conducted concurrently or even synchronously.

[0612] It is therefore to be understood that numerous modifications may be made to the illustrative examples and that other arrangements may be devised without departing from the spirit and scope of the technology.

TABLE-US-00004 REFERENCE SIGNS LIST patient 1000 bed partner 1100 patient interface 3000 seal-forming structure 3100 plenum chamber 3200 chord 3210 superior point 3220 positioning and stabilising structure 3300 vent 3400 connection port 3600 forehead support 3700 patient interface 3800 nasal prong 3810 air supply lumens 3820 RPT device 4000 external housing 4010 upper portion 4012 lower portion 4014 panel 4015 chassis 4016 handle 4018 pneumatic block 4020 air filter 4110 inlet air filter 4112 outlet air filter 4114 muffler 4120 inlet muffler 4122 outlet muffler 4124 outlet 4130 pressure generator 4140 blower 4142 motor 4144 anti - spill back valve 4160 air circuit 4170 supplemental oxygen 4180 electrical components 4200 Printed Circuit Board Assembly (PCBA) 4202 electrical power supply 4210 input devices 4220 central controller 4230 clock 4232 therapy device controller 4240 protection circuits 4250 memory 4260 transducers 4270 pressure sensor 4272 flow rate sensor 4274 motor speed transducer 4276 data communication interface 4280 remote external communication network 4282 local external communication network 4284 remote external device 4286 local external device 4288 output devices 4290 display driver 4292 display 4294 humidifier connector 4296 algorithms 4300 pre-processing module 4310 interface pressure estimation algorithm 4312 vent flow rate estimation 4314 leak flow rate estimation 4316 respiratory flow rate estimation 4318 therapy engine module 4320 phase determination algorithm 4321 waveform determination algorithm 4322 ventilation determination algorithm 4323 inspiratory flow limitation determination algorithm 4324 apnea / hypopnea determination algorithm 4325 snore determination algorithm 4326 airway patency determination algorithm 4327 target ventilation determination algorithm 4328 therapy parameter determination algorithm 4329 therapy control module 4330 methods 4340 humidifier 5000 humidifier inlet 5002 humidifier outlet 5004 humidifier base 5006 reservoir 5110 conductive portion 5120 humidifier reservoir dock 5130 locking lever 5135 water level indicator 5150 humidifier transducer 5210 air pressure sensor 5212 air flow rate transducer 5214 temperature sensor 5216 heating element 5240 humidifier controller 5250 central humidifier controller 5251 heating element controller 5252 air circuit controller 5254 external housing 5300 upper portion 5302 lower portion 5304 lid 5306 chassis 5310 vertical chassis wall 5312 chamber inlet port 5314 chassis peripheral wall 5316 free end 5318 inner chassis wall portion 5320 superior facing surface 5322 end cap 5330 main cap wall 5332 air inlet port 5334 inner surface 5336 external annular port wall 5338 inner peripheral wall 5340 free end 5342 locating feature 5344 resilient seal 5360 liquid trap portion 5362 first lip 5364 air inlet port portion 5366 second lip 5368 flange portion 5370 peripheral seal portion 5372 seal runner portion 5374 liquid trap 5380 vertical separation 5382 superior portion 5384 lateral portion 5386 inverted receptacle 5600 closed end 5602 open end 5604 receptacle wall 5606 drain hole 5608 interior trap wall 5700 baffle portion 5800 baffle extension 5802 radially extending baffle portion 5804 baffle member 5806 baffle legs 5808 liquid trap partition 5850 first portion 5852 second portion 5854 upright intermediary wall 5856 dividing wall 5858 partition wall 5860 first gap 5862 second gap 5864 first liquid trap catchment 5870 second liquid trap catchment 5872 third liquid trap catchment 5874 moveable barrier 5900 barrier body 5902 pivot 5904 stored position 5910 closed position 5912 secondary closure element 5950