RESPIRATORY DEVICE WITH IMPROVED HUMIDIFICATION OF THE RESPIRATION GAS

Abstract

The invention relates to a respiratory device (10) for the artificial respiration of a patient (12), comprising: —a respiration gas source assembly (15, 62), —a flow-changing device (16), —a humidifier device (38) which is designed to increase the value of the absolute humidity of the inspiratory respiration gas flow (AF), said humidifier device (38) having a liquid store (40) and an evaporation device (76) with a variable output for this purpose, —a respiration gas line assembly (30), —a proximal temperature sensor (48) which detects the temperature of the respiration gas flow (AF) in the proximal longitudinal end region (30a) of the respiration gas line assembly (30), —a humidity sensor assembly (66) which directly or indirectly detects the absolute humidity of the inspiratory respiration gas flow (AF), —a flow sensor (44), and —a controller (18) which is designed to control the operational output of the evaporation device (76)

Claims

1. A ventilation apparatus for artificial ventilation of a patient, comprising: a respiratory gas source arrangement that furnishes an inspiratory respiratory gas for artificial ventilation of the patient; a flow modification apparatus that is embodied to generate and to quantitatively modify an inspiratory respiratory gas flow; a humidification apparatus that is embodied to quantitatively increase the absolute moisture content of the inspiratory respiratory gas flow, the humidification apparatus comprising for that purpose a liquid reservoir and a modifiable-power-level evaporation apparatus; a respiratory gas conduit arrangement having a proximal longitudinal end located closer to the patient during operation and having a distal longitudinal end located farther from the patient during operation, in order to convey the inspiratory respiratory gas flow from the humidification apparatus to the patient; a proximal temperature sensor that is embodied to detect the temperature of the respiratory gas flow in the proximal longitudinal end region of the respiratory gas conduit arrangement; a humidity sensor arrangement that is embodied to detect at least one humidity state value of the inspiratory respiratory gas flow which indirectly or directly represents an absolute moisture content of the inspiratory respiratory gas flow; a flow sensor that is embodied to quantitatively detect the respiratory gas flow; a control apparatus which is signal-transferringly connected to the proximal temperature sensor, to the humidity sensor arrangement, and to the flow sensor, and which is embodied to control the operating power level of the evaporation apparatus depending on a predefined setpoint moisture content of the respiratory gas and depending on signals of the proximal temperature sensor, of the humidity sensor arrangement, and of the flow sensor, the humidity sensor arrangement being arranged upstream, in an inspiration direction of the respiratory gas flow, from the humidification apparatus and being embodied to detect the humidity state value upstream from the humidification apparatus; the ventilation apparatus comprising at least one ambient temperature sensor that is embodied to detect the temperature of the environment of the ventilation apparatus; the control apparatus being signal-transferringly connected to the at least one ambient temperature sensor and being embodied to control the operating power level of the evaporation apparatus, in addition to the dependences already recited, additionally depending on signals of the at least one ambient temperature sensor.

2. The ventilation apparatus according to claim 1, wherein it comprises an input apparatus for inputting a setpoint temperature of the respiratory gas flow in the proximal longitudinal end region of the respiratory gas conduit arrangement and/or for inputting a setpoint moisture content of the respiratory gas and/or for inputting a setpoint respiratory gas flow.

3. The ventilation apparatus according to claim 2, wherein it comprises an input apparatus for inputting a setpoint temperature of the respiratory gas flow in the proximal longitudinal end region of the respiratory gas conduit arrangement, and comprises a data memory which is queryable by the control apparatus and in which a correlation between temperature values of the respiratory gas flow in the proximal longitudinal end region of the respiratory gas conduit arrangement and associated setpoint moisture values of the respiratory gas is stored.

4. The ventilation apparatus according to claim 1, wherein at least one inspiratory conduit portion of the respiratory gas conduit arrangement comprises a conduit heating apparatus with which the inspiratory conduit portion is heatable.

5. The ventilation apparatus according to claim 1, wherein the humidity sensor arrangement is arranged downstream, in an inspiration direction of the respiratory gas flow, from the respiratory gas source arrangement.

6. The ventilation apparatus according to claim 1, wherein the control apparatus is signal-transferringly connected to the evaporation apparatus and/or to an energy supply thereof and/or to at least one energy sensor that is embodied to detect an energy delivered to the evaporation apparatus, in such a way that the energy and/or power level currently being delivered to the evaporation apparatus is ascertainable by the control apparatus from signals that are transferred via the signal-transferring connection.

7. The ventilation apparatus according to claim 1, wherein the respiratory gas conduit arrangement comprises at its proximal end a coupling configuration for coupling the respiratory gas conduit arrangement to a patient interface, for instance an endotracheal tube, a larynx mask, or a combination tube, and the like, which transfers respiratory gas between the respiratory gas conduit arrangement and the patient; the control apparatus being embodied to ascertain, depending on operating parameters of the ventilation apparatus, in particular of the respiratory gas flow, a resultant state of the ventilation situation downstream, in an inspiration direction, from the coupling configuration, and to modify the operating power level of the evaporation apparatus depending on the ascertained result.

8. The ventilation apparatus according to claim 7, wherein the resultant state of the ventilation situation encompasses a resultant temperature of the conduit wall of the patient interface and/or of the respiratory gas flow.

9. The ventilation apparatus according to claim 8, wherein it comprises a data memory which is queryable by the control apparatus and in which operating parameter values of the respiratory gas flow are associated with resultant temperature values of the conduit wall of the patient interface and/or of the respiratory gas flow.

10. The ventilation apparatus according to claim 7, wherein the control apparatus ascertains the resultant state depending on: the temperature, detected by the proximal temperature sensor, of the respiratory gas flow in the proximal longitudinal end region of the respiratory gas conduit arrangement; the magnitude of the respiratory gas flow detected by the flow sensor; and the predefined setpoint moisture content of the respiratory gas.

11. The ventilation apparatus according to claim 7, wherein the control apparatus ascertains the resultant state depending on the ambient temperature detected by the ambient temperature sensor.

12. The ventilation apparatus according to claim 7, wherein the control apparatus ascertains the resultant state for an ascertainment location located closer to the proximal end of the patient interface than to its distal end.

13. The ventilation apparatus according to claim 7, wherein the control apparatus ascertains the resultant state for a portion of the patient interface which is located between the coupling configuration and the entry point of the patient interface into the body of the patient.

14. The ventilation apparatus according to claim 7, wherein at least one inspiratory conduit portion of the respiratory gas conduit arrangement comprises a conduit heating apparatus with which the inspiratory conduit portion is heatable, and wherein the control apparatus is embodied to modify the temperature of the respiratory gas at the proximal temperature sensor, and for that purpose the operating power level of the conduit heating apparatus, depending on the ascertainment result.

15. The ventilation apparatus according to claim 4, wherein the control apparatus is embodied to control the operating power level of the conduit heating apparatus depending on a predefined setpoint temperature of the respiratory gas flow in the proximal longitudinal end region of the respiratory gas conduit arrangement.

16. The ventilation apparatus according to claim 12, wherein the control apparatus ascertains the resultant state for the proximal end of the patient interface.

17. The ventilation apparatus according to claim 14, wherein the control apparatus is embodied to control the operating power level of the conduit heating apparatus depending on a predefined setpoint temperature of the respiratory gas flow in the proximal longitudinal end region of the respiratory gas conduit arrangement.

Description

[0071] The present invention will be explained in further detail below with reference to the appended drawings, in which:

[0072] FIG. 1 schematically depicts a ventilation apparatus according to the present invention, configured for artificial ventilation of a patient; and

[0073] FIG. 2 schematically depicts the inspiratory respiratory gas conduit branch of the ventilation apparatus of FIG. 1.

[0074] In FIG. 1, an embodiment according to the present invention of a ventilation apparatus is labeled in general with the number 10. Ventilation apparatus 10 serves, in the example depicted, for artificial ventilation of a human patient 12.

[0075] Ventilation apparatus 10 comprises a housing 14 in which an intake opening 15 is embodied and in which a flow modification apparatus 16 and a control device 18 (not visible from outside because of the opaque housing material) are received. Intake opening 15 allows flow modification apparatus 16 to take in ambient air from external environment U of the ventilation apparatus and, after purification known per se by means of filters, to deliver it as respiratory gas to patient 12. Intake opening 15 is therefore a respiratory gas source arrangement for purposes of the present Application.

[0076] An ambient temperature sensor 17, which measures the temperature of the air of environment U and transfers it to sensor apparatus 18, is located in intake opening 15.

[0077] Flow modification apparatus 16 is constructed in a manner known per se and can comprise a pump, a compressor, a fan 52, a pressure vessel, a reduction valve 54 (see FIG. 2), and the like. Ventilation apparatus 10 furthermore comprises, in a manner known per se, an inspiration valve 20 and an expiration valve 22.

[0078] Control device 18 is usually implemented as a computer or microprocessor. It encompasses a data memory, labeled 19 in FIG. 1, so that data necessary for the operation of ventilation apparatus 10 can be stored and retrieved as necessary. In a network operation context, data memory 19 can also be located outside housing 14 and can be connected to control device 18 by a data transfer connection. The data transfer connection can be constituted by a cable link or a radio link. In order to prevent disruptions of the data transfer connection from having an effect on the operation of ventilation apparatus 10, however, data memory 19 is preferably integrated into control device 18 or at least received in the same housing 14 as that device.

[0079] Ventilation apparatus 10 comprises an input apparatus 24, which in the example depicted in FIG. 1 is represented by a keyboard, for inputting data into ventilation apparatus 10 or more precisely into control device 18. As will be explained in further detail below, the keyboard is not the only data input of control device 18. Control device 18 can in fact obtain data through a variety of data inputs, for instance via a network line, a radio link, or via sensor terminals 26 that will be discussed in detail below.

[0080] Ventilation apparatus 10 can comprise an output device 28, in the example depicted a display screen, for outputting data to the therapist providing care.

[0081] For artificial ventilation, patient 12 is connected to ventilation apparatus 10, more precisely to flow modification apparatus 16 in housing 14, via a respiratory gas conduit arrangement 30. Patient 12 is intubated for that purpose by means of an endotracheal tube constituting a patient interface 31. A proximal longitudinal end 31a of patient interface 31 discharges inspiratory respiratory gas flow AF into the lungs of patient 12. The expiratory respiratory gas flow also flows through proximal longitudinal end 31a into the respiratory gas conduit arrangement.

[0082] A distal longitudinal end 31b of patient interface 31 is embodied for connection to respiratory gas conduit arrangement 30. From location 31c downstream (in an inspiration direction) to proximal longitudinal end 31a, the patient interface is surrounded by the body of patient 12. This means conversely that from its distal longitudinal end 31b to location 31c, patient interface 31 is exposed to external environment U and is in (predominantly convective) thermally transferring communication therewith.

[0083] Ventilation conduit arrangement 30 comprises an inspiration hose 32 through which fresh respiratory gas can be directed from flow modification apparatus 16 into the lungs of patient 12. Inspiration hose 32 can be interrupted, and can comprise a first inspiration hose 34 and a second inspiration hose 36 between which a humidification apparatus 38, for controlled humidification and optionally also temperature control of the inspiratory respiratory gas delivered to patient 12, can be provided. Humidification apparatus 38 can be connected to an external liquid reservoir 40 by way of which water for humidification, or also a medication e.g. to inhibit inflammation or to dilate the airways, can be delivered to humidification apparatus 38. When the present ventilation apparatus 10 is used as an anesthesia ventilation apparatus, it is thereby possible to deliver volatile anesthetics to patient 12 in controlled fashion via ventilation apparatus 10. Humidification apparatus 38 ensures that the fresh respiratory gas is conveyed to patient 12 with a predetermined moisture content, optionally with addition of a medication aerosol, and at a predetermined temperature.

[0084] In the present example, second inspiration hose 36 is electrically heatable by a conduit heating apparatus 37. Conduit heating apparatus 37 can be controlled by control apparatus 18 for operation. Unlike what is said above, first inspiration hose 34 can also be heatable, and/or the at least one hose 34 and/or 36 can be heatable by a conduit heating apparatus 37 that is other than electric, for instance by having a heat exchange medium flow around it.

[0085] Respiratory gas conduit arrangement 30 further comprises, in addition to the aforementioned inspiration valve 20 and expiration valve 22, an expiration hose 42 by way of which metabolized respiratory gas is expelled from the lungs of patient 12 into external environment U.

[0086] At distal longitudinal end 30b of respiratory gas conduit arrangement 30, inspiration hose 32 is coupled to inspiration valve 20, and expiration hose 42 to expiration valve 22. Preferably only one of the two valves is respectively open simultaneously for passage of a gas flow. Actuation control of valves 20 and 22 is likewise accomplished by control device 18.

[0087] During a ventilation cycle, firstly expiration valve 22 is closed and inspiration valve 20 is opened for the duration of the inspiration phase, so that fresh inspiratory respiratory gas can be directed from housing 14 to patient 12. A flow of fresh respiratory gas is produced by flow modification arrangement 16 by controlled elevation of the pressure of the respiratory gas. As a result of the pressure elevation, the fresh respiratory gas flows into the lungs of patient 12 where it expands the body region in the vicinity of the lungs, i.e. in particular the thorax, against the individual elasticity of the body parts near the lungs. The gas pressure in the interior of the lungs of patient 12 also rises as a result.

[0088] At the end of the inspiration phase, inspiration valve 20 is closed and expiration valve 22 is opened. The expiration phase begins. Because the gas pressure of the respiratory gas present in the lungs of patient 12 has been elevated until the end of the inspiration phase, said gas flows into external environment U after expiration valve 22 is opened, while the gas pressure in the lungs of patient 12 decreases as the flow continues. When the gas pressure in lungs 12 reaches a positive end expiration pressure (PEEP) that is set on ventilation apparatus 10, i.e. a pressure slightly higher than atmospheric pressure, the expiration phase is terminated with the closing of expiration valve 22, and is followed by a further ventilation cycle.

[0089] The so-called ventilation tidal volume, i.e. the volume of respiratory gas for each breath, is delivered to patient 12 during the inspiration phase. The ventilation tidal volume multiplied by the number of ventilation cycles per minute, i.e. multiplied by the ventilation frequency, equals the volume per minute of artificial ventilation being performed in the present case.

[0090] Ventilation apparatus 10, in particular control device 18, is preferably embodied to repeatedly update or ascertain, during ventilation operation, ventilation operating parameters that characterize the ventilation operation of ventilation apparatus 10, in order to ensure that ventilation operation is coordinated as optimally as possible, at every point in time, with patient 12 who is respectively to be ventilated. Particularly advantageously, the determination of one or several ventilation operation parameters is made at the ventilation frequency, so that ventilation operating parameters that are current, and are thus optimally adapted to patient 12, can be furnished for each ventilation cycle.

[0091] Ventilation apparatus 10 can be data-transferringly connected for that purpose to one or several sensors that monitor the status of the patient and/or the operation of ventilation apparatus 10. A proximal flow sensor 44, which quantitatively detects the respiratory gas flow existing in respiratory gas conduit arrangement 30, is mentioned in FIG. 1 merely as an example of a number of possible sensors. Proximal flow sensor 44, preferably embodied as a differential pressure sensor, can be coupled by means of a sensor lead arrangement 46 to data inputs 26 of control device 18. Sensor lead arrangement 46 can, but does not need to, encompass electrical signal transfer leads. It can also comprise hose lines that transfer the gas pressure, existing on either side of flow sensor 44 in a flow direction, to data inputs 26, where those pressures are quantified by pressure sensors (depicted only in FIG. 2).

[0092] More precisely, in the preferred exemplifying embodiment respiratory gas conduit arrangement 30 comprises at its proximal longitudinal end region 30a a separately embodied Y-conduit portion 47, which is connected at its distal end region to second inspiration hose 36 and to expiration hose 42, and which is connected at its proximal end region to proximal flow sensor 44.

[0093] Proximal flow sensor 44 comprises at its proximal end region a coupling configuration 44a with which patient interface 31, which could also be a mask rather than a tube, is couplable to proximal flow sensor 44 and consequently to respiratory gas conduit arrangement 30.

[0094] Second inspiration hose 36 comprises, at its proximal longitudinal end region, a proximal temperature sensor 48 that measures the temperature of respiratory gas flow AF in second inspiration hose 36 as close as possible to patient 12, and transfers it to control apparatus 18.

[0095] Merely for the sake of completeness, be it noted that ventilation apparatus 10 according to the present invention can constitute a mobile ventilation apparatus 10 and can be received on a rollable frame 50.

[0096] FIG. 2 is a schematic view of the inspiratory conduit branch of ventilation apparatus 10 of FIG. 1.

[0097] Flow modification apparatus 16 encompasses a fan 52 and a reduction valve 54 located downstream therefrom in an inspiration direction. It is also possible for only fan 52 to be provided. For operation, control apparatus 18 can apply control to fan 52 and to reduction valve 54 via respective leads 56 and 58.

[0098] Fan 52 can take in ambient air from external environment U through intake opening 15. Additionally or alternatively, gas, for instance pure oxygen, from a reservoir vessel 62 can be used via a valve 60 as a respiratory gas or can be mixed into the ambient air that is taken in. In the exemplifying embodiment depicted, intake opening 15 and reservoir vessel 62 therefore together constitute a respiratory gas source arrangement.

[0099] The ambient air that is taken in is purified in ventilation apparatus 10 in a manner known per se, in filters that are not depicted.

[0100] Inspiration valve 20, which is controllable by control apparatus 18 via a lead 64 for opening and closing, is located downstream (in an inspiration direction) from flow modification apparatus.

[0101] Farther downstream in an inspiration direction, inspiration valve 20 is followed by first inspiration hose 34.

[0102] Downstream in an inspiration direction from ventilation apparatus 38 in the narrower sense, ventilation apparatus 10 encompasses a humidity sensor arrangement 66 that, in the economically preferred instance depicted, encompasses a sensor 68 for ascertaining the relative humidity of inspiratory respiratory gas flow AF and a temperature sensor 70 for ascertaining the respiratory gas temperature in the region in which humidity is detected by sensor 68. Alternatively, humidity sensor arrangement 66 could encompass only one sensor for detecting the absolute moisture content of the respiratory gas, but for cost reasons this is not preferred.

[0103] Humidity sensor arrangement 66 detects, along with the relative moisture content and the temperature of the respiratory gas upstream from humidification apparatus 48, the relative moisture content and the temperature of the respiratory gas after respiratory gas sources 15 and 62 but before humidification measures are taken by ventilation apparatus 10. Humidity sensor arrangement 66 can be arranged in the housing, shown in FIG. 1, of humidification apparatus 38, but upstream from humidification apparatus 38, which is constituted by a humidification chamber 72 having a liquid reservoir 74 to which thermal energy for evaporating liquid can be delivered via a thermal evaporation apparatus 76 in the form of a heating plate.

[0104] The detected values of sensors 68 and 70 are transferrable via leads 78 and 80 to control apparatus 18.

[0105] From the detected values thereby obtained for the relative moisture content and the temperature of the respiratory gas before reaching humidification apparatus 38, control apparatus 18 can ascertain the absolute moisture content of the respiratory gas and compare it to a desired setpoint moisture content of the respiratory gas.

[0106] The setpoint moisture content of the respiratory gas can be obtained, for example, from a data correlation, stored in data memory 19, of signals of proximal temperature sensor 48, and optionally also of the proximal respiratory gas flow detected by proximal flow sensor 44. Alternatively, a desired setpoint moisture content of the respiratory gas can also be inputted manually via input apparatus 24.

[0107] Based on the setpoint moisture content of the respiratory gas, and also depending on the signals of proximal temperature sensor 48 (which are transferred via a lead 82 to control apparatus 18), of humidity sensor arrangement 66, and of proximal flow sensor 44, control apparatus 18 ascertains an operating power level that is to be delivered to evaporation apparatus 76 in the form of a heating plate. Control apparatus 18 applies control via a lead 84 to an energy supply 86 of evaporation apparatus 76 in accordance with the ascertained operating power level. By way of lead 84, control apparatus 18 receives information regarding the operating power level delivered to evaporation apparatus 76, for example in the form of the voltage applied to evaporation apparatus 76 and the current intensity flowing to it. Energy supply apparatus 86 can deliver a variable power level to evaporation apparatus 76, for example by pulse width modulation. In a context of pulse width modulation, the voltage applied to evaporation apparatus 76 is a time-averaged voltage.

[0108] Liquid is evaporated from liquid reservoir 74 by evaporation apparatus 76, and is entrained by respiratory gas flow AF that flows over liquid reservoir 74.

[0109] In order to account for heat losses from evaporation apparatus 76 to environment U, control apparatus 18 ascertains the energy to be delivered per unit time to evaporation apparatus 76 via energy supply apparatus 86 additionally in consideration of the ambient temperature ascertained by ambient temperature sensor 17.

[0110] In order to ascertain the operating power level to be delivered to evaporation apparatus 76 depending on the setpoint moisture content of the respiratory gas, and further depending on the proximal respiratory gas temperature, the absolute moisture content detected indirectly by humidity sensor arrangement 66, the proximal respiratory gas flow detected by proximal flow sensor, and further depending on the ambient temperature, a corresponding data correlation, which was determined previously in the laboratory for a ventilation apparatus 10 of the same design by parameter variation under controlled conditions, is stored in data memory 19.

[0111] It is therefore to be assumed that as a result of the operation of evaporation apparatus 76, controlled by control apparatus 18 in accordance with the parameters recited, inspiratory respiratory gas flow AF leaves humidification apparatus 38 with the setpoint moisture content. The inspiratory respiratory gas flow then enters second inspiration hose 36, which can be heated by conduit heating apparatus 37. The operation of conduit heating apparatus 37 is controllable by control apparatus 18 by means of a lead 88 in accordance with the temperature detected by proximal temperature sensor 48, in such a way that the proximal respiratory gas temperature detected by proximal temperature sensor 48 is above the dew point temperature of the humidified inspiratory respiratory gas flow AF.

[0112] The dew point temperature can be ascertained, based on the assumption that the respiratory gas exhibits the setpoint moisture content after passing through humidification apparatus 38, based on the proximal respiratory gas temperature detected by proximal temperature sensor 48 and further based on a dew point temperature curve stored in data memory 19. What is obtained from the dew point temperature curve is thus a setpoint temperature above which the temperature at proximal temperature sensor 48 should remain, preferably in fact should remain with a certain safety margin.

[0113] Storage of a dew point temperature curve in data memory 19 does not necessarily mean storage of a continuously differentiable curve. It is sufficient to store a dew point temperature curve that is approximated by a sufficient number of interpolation points, for example as a table. It is also possible to store, for the dew point temperature, an approximate mathematical function with which a dew point temperature can be ascertained based on a known absolute moisture content or on a known value pair of a relative moisture content and an associated temperature.

[0114] One problem in terms of properly supplying the patient with respiratory gas that is sufficiently humidified, but not over-humidified, is patient interface 31. Patient interface 31 is not heatable, as second inspiration hose 36 is, nor is it equipped with any sensors that might detect the ventilation state in patient interface 31. The reason for this is the usual nature of patient interface 31 as a disposable or single-use interface.

[0115] Specifically when ambient temperatures are very low, for instance in emergency situations, at the least the portion exposed to external environment U, between distal longitudinal end 31b of patient interface 31 and the entry of patient interface 31 into patient 12 at location 31c, is therefore greatly influenced by the ambient temperature. In this portion, patient interface 31 can be so severely cooled by the ambient temperature that an undesirable “rain out” occurs in patient interface 31. This undesired condensation of liquid out of inspiratory respiratory gas flow AF as a rule will occur most readily on the conduit wall of patient interface 31 which is cooled by ambient air. It is also not to be excluded, however, that respiratory gas flow AF in patient interface 31 cools to such an extent, under the influence of the ambient temperature, that fogging occurs in respiratory gas flow AF.

[0116] In order to avoid such undesired condensation of liquid in patient interface 31, control apparatus 18 is embodied to ascertain, on the basis of operating parameters of the ventilation apparatus which are transferred to it by the available sensors and in particular based on inspiratory respiratory gas flow AF, a resultant state, produced under the influence of the ambient temperature, of the ventilation situation in patient interface 31 downstream (in an inspiration direction) from coupling configuration 44a, and to determine on the basis of that ascertained resultant state whether condensation in patient interface 31 is to be expected.

[0117] For that purpose, either empirically ascertained data correlations or an analytically or numerically solvable equation system, constituting a model description of the thermal state of patient interface 31 during operation depending on operating data of ventilation apparatus 10 and its environment U, can be stored in data memory 19.

[0118] In a particularly simple and rapidly ascertainable calculation model, the resultant state of patient interface 31 is a resultant temperature of patient interface 31 which is ascertainable, for example, based on the proximal respiratory gas temperature at temperature sensor 48, in further consideration of the design configuration of patient interface 31 including the materials used therein, and in consideration of the ambient temperature measured by ambient temperature sensor 17. The inspiratory respiratory gas flow AF detected by proximal flow sensor 44, and if desired even an expiratory respiratory gas flow likewise detected by proximal flow sensor 44, can also be utilized in order to ascertain the resultant temperature.

[0119] Control apparatus 18, to which the dew point temperature of inspiratory respiratory gas flow AF is already available by way of the above-described control of ventilation apparatus 10, can thus assume that a risk of condensation in patient interface 31 is immediately imminent if a resultant temperature of patient interface 31 at a point located upstream in an inspiration direction from distal longitudinal end 31b (said temperature being ascertained based on an empirically ascertained data correlation and/or based on a thermodynamic model) falls below the dew point temperature. For the safety of the patient, it is preferably not the dew point temperature directly, but rather a threshold temperature that is a dew point temperature raised by a predetermined safety margin, that is utilized.

[0120] For the instance in which control apparatus 18 ascertains in this manner that condensation is definitely, or with a preponderant probability, or with more than a predetermined limit probability, occurring in patient interface 31, control apparatus 18 is embodied to decrease the operating power level delivered to evaporation apparatus 76. The amount by which the operating power level of evaporation apparatus 76 is decreased can be selected to be greater, the greater the condensation risk based on the ascertainment result, for example the greater the degree to which the resultant temperature of patient interface 31 quantitatively falls short of the threshold temperature or even the dew point temperature.

[0121] In addition, control apparatus 18 can also increase the operating power level of conduit heating arrangement 37 in order to increase the temperature of inspiratory respiratory gas flow AF on the way to proximal longitudinal end 30a of respiratory gas conduit arrangement 30. But because the present control apparatus 18 is intended to be able to prevent condensation of respiratory gas in patient interface 31 even for inspiration hoses that are not heatable, the decrease in the operating power level of evaporation apparatus 76 is implemented in all cases.