METHOD AND DEVICE FOR MEASUREMENT OF EXHALED RESPIRATORY GAS TEMPERATURE FROM SPECIFIC REGIONS OF THE AIRWAY

Abstract

An Exhaled Breath Temperature (EBT) monitor for the measurement of portions of exhaled respiratory gas temperature during a single exhalation, the monitor comprising: An inlet channel for receiving a stream of exhaled respiratory gas, a plurality of measurement chambers, temperature sensors located within more than one measurement chamber adapted for measuring the temperature of exhaled respiratory gas, a plurality of valves intermediate the air channel and each measurement chamber, configured to selectively pass portions of the gas stream in to each chamber and a control unit, configured to operate the valves and record the measurements of the temperature sensor

Claims

1. A system for measuring exhaled respiratory gas temperature during a single exhalation, the system comprising: an inlet channel for receiving a stream of exhaled respiratory gas; a plurality of measurement chambers, each of a predetermined set of thermal characteristics; a temperature sensor located within each measurement chamber adapted for measuring the temperature of exhaled respiratory gas in that measurement chamber; a valve intermediate the inlet channel and each said measurement chamber; and a control unit configured to operate the valves to pass predetermined portion(s) of the exhaled respiratory gas during a single exhalation of breath to respective measurement chamber(s).

2. A system for measuring exhaled respiratory gas temperature during a single exhalation, the system comprising: an inlet channel for receiving a stream of exhaled respiratory gas; a plurality of measurement chambers, each of the same predetermined set of thermal characteristics; a temperature sensor located within more than one measurement chamber adapted for measuring the temperature of exhaled respiratory gas in that measurement chamber; a valve intermediate the inlet channel and each said measurement chamber; and a control unit configured to operate the valves to pass two or more predetermined portion(s) of the exhaled respiratory gas corresponding to separate airway sections during a single exhalation of breath to respective measurement chamber(s).

3. The system of claim 1 further comprising a flow measurement device.

4. The system of claim 3 wherein the control unit is configured to monitor the flow measurement device and calculate the volume of gas inhaled and, during exhalation, to operate the valves in order to initiate passage of predetermined portion(s) of the volume of the exhaled gas to respective measurement chamber(s).

5. The system of claim 3 wherein the flow measurement device is a pressure sensor.

6. The system of claim 1, wherein the temperature sensors are thermistors.

7. The system of claim 1, wherein the temperature sensors are thermocouples.

8. The system of claim 1, wherein the measurement chambers are constructed of a low thermal mass material.

9. The system of claim 1, wherein the valves are pneumatically operated.

10. The system of claim 9, wherein the valves comprise an inflatable membrane within the inlet of each measurement chamber.

11. The system of claim 1, wherein the control unit and valves are arranged so that one or more portions of the exhaled gas are discharged without measurement.

12. The system of claim 1, wherein the system further comprises an electronic processor for processing electronic signals from the temperature sensors and a display for displaying signals from the processor.

13. The system of claim 1, further configured to provide visual or audible prompts to the patient to instruct them to inhale and exhale at appropriate times, and to repeat the process.

14. A method of measuring exhaled respiratory gas temperature during a single exhalation, the method comprising: an inlet channel receiving a stream of exhaled respiratory gas; operating a plurality of valves, each intermediate the inlet channel and a respective separate measurement chamber of a predetermined set of thermal characteristics and that chamber having a temperature sensor adapted for measuring the temperature of exhaled respiratory gas in that measurement chamber, to pass predetermined portion(s) of the exhaled respiratory gas during a single exhalation of breath to respective measurement chamber(s).

15. The method of claim 14 wherein the predetermined set of thermal characteristics is the same for all the chambers, and wherein each of the plurality of valves pass two or more predetermined portion(s) of the exhaled respiratory gas corresponding to separate airway sections during a single exhalation of breath to respective measurement chamber(s).

16. The method of claim 14, further comprising: detecting a start of an exhalation operation, operating a plurality of measurement chambers each of a predetermined set of thermal characteristics to isolate predetermined portion(s) of the exhaled gas to the respective measurement chamber, and recording the output of temperature sensors located within the measurement chambers.

17. The method of claim 14, further comprising measuring the total volume of inhaled gas, measuring the cumulative volume of exhaled gas and operating the valves to pass predetermined fractions of the total volume of respiratory gas in an exhalation into separate measuring chambers.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0088] In order that the invention may be more readily understood, a description is now given, by way of example only, reference being made to various embodiments of the present invention, in which:

[0089] FIG. 1 is a diagram of an Exhaled Breath Temperature measurement system of the present invention.

[0090] FIG. 2 is a diagram of a measurement unit which forms part of the measurement system of the present invention.

[0091] FIG. 3 is another diagram of the Exhaled Breath Temperature measurement system of the present invention showing greater detail of the control unit.

[0092] FIGS. 4A to C show layout drawings of one embodiment of the measurement unit with top, side and end views.

[0093] FIGS. 5A to F is a set of diagrams of the measurement unit illustrating the steps during operation.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

[0094] Referring now to FIG. 1, an exemplary arrangement shows a measurement unit 100, comprising measurement chambers 130-133, temperature sensors t1, t2 and t3, flow sensor 150, valves V1 to V4.

[0095] Control unit 190 comprises electronic circuitry configured to operate the valves V1 to V4 and to record the values of the temperature sensors t1 to t3 and the flow sensor 150. Control unit 190 may optionally comprise a compressed air supply 230 to operate pneumatic valves. The control unit may also include digital circuitry to convert the temperature readings into digital values and transmit them to a processor.

[0096] Control unit 190 is connected to measurement unit 100 by data cables 170, to transmit the temperature and flow sensor readings, and in this example flexible tubing 180 to operate pneumatic valves. If another type of valve is used, then appropriate connections would be required.

[0097] FIG. 1 also shows processor 200 and display 210. The processor receives digital temperature and flow readings from the control unit 190 and may collect the readings on a storage medium. Software on the processor may be configured to display temperature readings as a graph, provide medical diagnostic suggestions based on recorded temperatures and allow configuration of the control unit. The processor may be in a separate unit, for example a personal computer, or incorporated into the control unit 190.

[0098] FIG. 2 shows measurement unit 100, comprising measurement chambers 130-133, temperature sensors t1, t2 and t3, flow sensor 150, valves V1 to V4. Temperature sensor t1 is positioned in measurement chamber 131, sensor t2 is located in air inlet channel 110 and sensor t3 is located in measurement chamber 133.

[0099] Temperature sensor t1 is positioned in measurement chamber 131, sensor t2 is located in air inlet channel 110 and sensor t3 is located in measurement chamber 133. Additional sensors could be installed in additional measurement chambers if required.

[0100] The valves V1 to V4 are positioned between the air inlet channel 110 and the measurement chambers 130 to 133. Valve V2 is shown open in this example while V1, V3 and V4 are shown as closed. When a valve is open, air can pass between the inlet channel and the respective measurement chamber.

[0101] In a preferred embodiment, the valves may be pneumatically operated, such as an inflatable membrane that can expand to close the top of the measurement chamber. Compressed air connectors such as 160 are shown connected to each valve. A pneumatic valve operated by compressed air at ambient temperature will cause negligible heat gain or loss in the measurement chamber and will produce no electrical interference with the temperature sensors.

[0102] FIG. 3 shows a typical example of the exhaled breath temperature measurement system 300, showing the same referenced features as FIG. 1. In addition FIG. 3 shows a compressed air supply 230 to provide compressed air for pneumatic valves, and within control unit 190 are shown thermosensor control circuits 310, digital-to-analogue 320 and analogue-to-digital circuitry 330, a USB interface 340, valve control circuitry 350 and flow sensor control circuits 360.

[0103] FIGS. 4A to 4C show three orthogonal projections of an exemplary embodiment of the measurement unit.

[0104] In FIG. 4A, the top view of the measurement unit 100 measurement chambers 131 and 133 are positioned opposite one another and equidistantly on either side of the air inlet channel 110. Each of measurement chambers 131 and 133 is connected to the air inlet channel by a short connection channel (not numbered) of the same diameter as the inlet channel. This arrangement ensures that exhaled gas passing to measurement chambers 131 and 133 has passed through the same length of air channel in order to minimize variations in recorded temperature due to heat absorption by the construction material of the channel.

[0105] In this exemplary embodiment, measurement chambers 130 and 132 are positioned at other locations and connected to the air inlet channel. In this embodiment measurement channels 130 and 132 do not contain temperature sensors, but are constructed with the same material and diameters as measurement channels 131 and 133 in order to ensure that the path travelled by the exhaled gas during inhalation and exhalation meets a similar flow resistance, so that determination of the volume of each portion of exhaled gas are not significantly affected by changes in pressure drop along the flow path.

[0106] Preferably, the measurement unit is constructed from a biomaterial with low thermal conductivity in order to minimize the heat transfer from the measurement chambers.

[0107] FIGS. 4B and 4C show vertical side and end views of the measurement unit, illustrating that the four measurement chambers 130 to 133 and valves V1 to V4 are arranged parallel to one another in a vertical alignment, perpendicular to the air inlet channel 110.

[0108] FIG. 5 shows the operation of the valves in steps A to F in an exemplary embodiment of the measurement unit 100. For clarity, only the valves V1 to V4 are referenced on the drawings, for other features refer back to FIGS. 1 to 3.

[0109] During measurement, a patient may inhale and exhale through a replaceable mouthpiece (not shown) connected to air inlet channel 110. The software in processor 200 will signal to control unit 190 when to open or close each valve, and will also record temperatures and flow from the sensors.

[0110] FIG. 5A shows that, during inhalation, valve V1 opens to allow air to pass to the patient, valves, V2, V3 and V4 are closed. Software in the processor 200 monitors the flow sensor 150 to calculate the volume of air inhaled. After completion of the inhalation, the software calculates the total volume of the inhaled air. Depending on operator settings, the software will calculate the volumes of exhaled air that are required to be passed through each measurement chamber. For example, if the operator is interested in the temperature of the first third and last third of a breath, in order to distinguish the airway temperature of the lungs from the alveolar temperature, then the software would calculate three equal volumes of one third each of the total.

[0111] To reduce errors in the temperature measurements caused by thermal inertia of the sensors themselves and the measurement chambers, preferably the volumes requiring measurement are selected to be equal.

[0112] The start of exhalation may be automatically detected by monitoring a change of direction indicated by the flow sensor, or the patient may be prompted when to exhale by visual and/or audible prompts.

[0113] FIG. 5B shows that, during exhalation, valve V2 opens up, V1, V3 and V4 are closed, while the first portion of air is exhaled; the temperature of t1 and t2 are recorded by processor 200.

[0114] FIG. 5C shows that, once the processor 200 has determined that the first portion of air has passed through the inlet channel, valve V3 is opened, V1, V2 and V4 are closed, while the second volume of air is exhaled. In this example, only the temperature t2 is recorded as the air during transition from airway to alveolar is not of interest.

[0115] FIG. 5D shows that, once the processor 200 has determined that the second portion of air has passed through the inlet channel, valve V4 opens up, V1, V2 and V3 are closed, while the third (last) portion of air is exhaled; t3 and t2 are recorded by the control unit 190.

[0116] FIG. 5E shows that, after the third volume of air has passed through the inlet channel, all valves are closed to prevent further air movement and the recorded temperatures may be displayed on the display 210 attached to the processor 200, and comparisons of interest to the operator such as the difference between t1 and t3 as well as all other derivative variables may be calculated by the processor and displayed.

[0117] FIG. 5F: After use, all valves are opened to allow the measurement chambers and the air inlet channel to reach equilibrium temperature with the atmosphere before further use.

[0118] Thus, presently the air volume is measured during a deep inspiration and the processor 200 computer drives the valve system to slice the exhaled flow into relative portions from the upper and lower airways (typically 10 to 33% of the total volume is assigned for the upper airways, and 33 to 70% of the volume for the peripheral airways).

[0119] In a variant, the air volume from the upper airways is set as an absolute value (in the range 250-350 mL), while the volume of the peripheral airways is still a proportion of the total volume to be exhaled (e.g. 70%). This may provide measurements closer to reality, to more accurately reflect the anatomic relationships in the human respiratory system: while the volume of the peripheral airways can vary widely between individuals depending on age, height, gender, respiratory morbidities (900-4000 mL), the volume of the upper airways remains relatively constant somewhere between 250 and 350 mL, the measurements closer to the anatomical peculiarities of the large and small airways. In respiratory pathology, the volume of the upper and large airways is more or less constant, while there is a lot of variability in the remainder of the bronchial tree.

[0120] The present invention in its various aspects is as set out in the appended claims.