SENSOR ARRANGEMENT, MEDICAL APPARATUS, EXHALATION VALVE, AND METHOD FOR DETERMINING A CARBON DIOXIDE CONCENTRATION IN A MEASUREMENT GAS

Abstract

A sensor arrangement (10) for a medical device (12), includes a sensor unit (11) for determining a carbon dioxide concentration in the measured gas, a branch line (14) for branching off the measured gas from a main line (15) of the medical device (12) and for sending the branched-off measured gas to the sensor unit (11). At least one heat and moisture exchanger filter (16, 17) filters the branched-off measured gas. A medical device (12) with the sensor arrangement (10), an exhalation valve (25) for the medical device (12) as well as a process for determining a carbon dioxide concentration are also provided.

Claims

1. A sensor arrangement for a medical device, the sensor arrangement comprising: a sensor unit for determining a carbon dioxide concentration in a measured gas, a branch line for branching off the measured gas from a main line of the medical device and for sending the branched-off measured gas to the sensor unit; and at least one heat and moisture exchanger filter for filtering the branched-off measured gas.

2. A sensor arrangement in accordance with claim 1, wherein the at least one heat and moisture exchanger filter is arranged in the branch line.

3. A sensor arrangement in accordance with claim 1, wherein the branch line has a main line-side end section for connecting the branch line to the main line and a sensor-side end section for connecting the branch line to the sensor unit, wherein the at least one heat and moisture exchanger filter is arranged at and/or in the main line-side end section.

4. A sensor arrangement in accordance with claim 1, wherein the branch line has a main line-side end section for connecting the branch line to the main line and a sensor-side end section for connecting the branch line to the sensor unit, wherein the at least one heat and moisture exchanger filter is a first heat and moisture exchanger filter at and/or in the main line-side end section and further comprising a second heat and moisture exchanger filter at and/or in the sensor-side end section.

5. A sensor arrangement in accordance with claim 4, wherein the first heat and moisture exchanger filter is arranged in the main line-side end section of the branch line in the form of a hose insert, wherein the branch line has, when viewed in the flow direction of the measured gas through the branch line, a larger internal diameter at an area of the heat and moisture exchanger filter than in an area located downstream of the heat and moisture exchanger filter.

6. A sensor arrangement in accordance with claim 5, wherein the internal diameter of the branch line has a value in a range of 2 mm to 4 mm at an area of the first heat and moisture exchanger filter and the internal diameter of the branch line has a value in a range of 0.5 mm to 2 mm downstream of the first heat and moisture exchanger filter.

7. A sensor arrangement in accordance with claim 1, wherein the at least one heat and moisture exchanger filter is configured in the form of a hose insert in the main line-side end section of the branch line, wherein the branch line has, when viewed in the flow direction of the measured gas through the branch line, a larger internal diameter in an area located upstream of the at least one heat and moisture exchanger filter than downstream of the at least one heat and moisture exchanger filter.

8. A sensor arrangement in accordance with claim 7, wherein the internal diameter of the branch line upstream of the at least one heat and moisture exchanger filter has a value in a range of 1.5 mm to 4 mm and the internal diameter of the branch line downstream of the at least one heat and moisture exchanger filter has a value in a range of 0.5 mm to 2 mm.

9. A sensor arrangement in accordance with claim 1, wherein the at least one heat and moisture exchanger filter has a length in a range of 8 mm to 20 mm and a width in a range of 2 mm to 6 mm.

10. A sensor arrangement in accordance with claim 1, wherein the branch line has a hose line with a length in a range of 80 cm to 150 cm.

11. A sensor arrangement in claim 1, wherein the branch line has a hose line made of silicone or at least predominantly formed of silicone.

12. A sensor arrangement in claim 1, wherein the branch line has a hose line with a PVC coating on an outer circumferential surface of the hose line.

13. A sensor arrangement in claim 1, wherein the branch line has a Luer lock fitting for establishing a fluid connection with the main line.

14. A sensor arrangement in claim 1, wherein the at least one heat and moisture exchanger filter comprises, a microporous plastic foam.

15. A medical device for ventilating a person, the medical device comprising: a main line for sending inhalation gas and for sending exhalation gas; and a sensor arrangement comprising: a sensor unit configured to determine a carbon dioxide concentration in a measured gas; a branch line configured to branch off the measured gas from the main line and to guide the branched-off measured gas to the sensor unit; and at least one heat and moisture exchanger filter configured to filter the branched-off measured gas.

16. A medical device in accordance with claim 15, wherein the main line has an inhalation gas line section for sending the inhalation gas and a total gas line section for sending the inhalation gas as well as the exhalation gas, wherein the branch line is configured for branching off the measured gas from the total gas line section.

17. A medical device in accordance with claim 16, wherein the at least one heat and moisture exchanger filter is located within the total gas line section.

18. A medical device in accordance with claim 16, wherein at least one part of the branch line extends within the main line from the total gas line section into the inhalation gas line section.

19. A medical device in accordance with claim 16, wherein an exhalation valve is configured in the total gas line section for releasing exhalation gas from the medical device into the area surrounding the medical device, wherein the at least one heat and moisture exchanger filter is formed in the exhalation valve.

20. A medical device in accordance with claim 19, wherein the branch line is connected to the exhalation valve for branching off the measured gas from the main line.

21. A medical device in accordance with claim 15, wherein the medical device is configured as a ventilator.

22. An exhalation valve for a medical device in accordance with claim 15, for releasing exhalation gas from the medical device into an area surrounding the medical device, the exhalation valve comprising, having a heat and moisture exchanger filter integrated into the exhalation valve for filtering a measured gas branched off from the medical device via the exhalation valve.

23. An exhalation valve in accordance with claim 22, further comprising: a valve port for connecting the branch line for branching off the measured gas from the main line of the medical device through the heat and moisture exchanger filter.

24. An exhalation valve in accordance with claim 223, wherein the integrated heat and moisture exchanger filter comprises a microporous plastic foam.

25. A process for determining a carbon dioxide concentration in a measured gas, the process comprising the steps of: providing a sensor arrangement comprising a sensor unit, a branch line configured to branch off the measured gas from a main line of a medical device and to guide the branched-off measured gas to the sensor unit, and a moisture exchanger filter configured to filter the branched-off measured gas; and determining the carbon dioxide concentration by measuring heat conductivity of the exhalation gas with the sensor unit.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In the Drawings:

[0040] FIG. 1 is a schematic view showing a medical device according to a first embodiment of the present invention;

[0041] FIG. 2 is a schematic view showing a medical device according to a second embodiment of the present invention,

[0042] FIG. 3 is a schematic view showing one of different sensor arrangements according to the present invention;

[0043] FIG. 4 is a schematic view showing another of different sensor arrangements according to the present invention;

[0044] FIG. 5 is a schematic view showing another of different sensor arrangements according to the present invention;

[0045] FIG. 6 is a schematic view showing a medical device according to a third embodiment of the present invention;

[0046] FIG. 7 is a schematic view showing a medical device according to a fourth embodiment of the present invention;

[0047] FIG. 8 is a diagram for explaining the manner of functioning of the present invention;

[0048] FIG. 9 is a diagram for explaining the manner of functioning of the present invention;

[0049] FIG. 10 is a diagram for explaining the manner of functioning of the present invention;

DESCRIPTION OF PREFERRED EMBODIMENTS

[0050] Elements having the same function and mode of operation are always provided with the same reference numbers in the figures.

[0051] FIG. 1 shows a medical device 12 in the form of a ventilator for ventilating a person 13 according to a first embodiment. The medical device 12 comprises a breathing mask 20 and a main line 15 for sending inhalation gas to the breathing mask 20 and for sending exhalation gas away from the breathing mask 20. The main line 15 has an inhalation gas line section 21 and an exhalation gas line section 23. A main pump 27 is formed in the inhalation gas line section 21 for feeding the inhalation gas to the breathing mask 20 or to the person 13. An exhalation valve is formed downstream of the main pump 27, when viewed in a flow direction of the inhalation gas. The exhalation valve 25 is attached to the gas mask 20. Only inhalation gas is sent in the inhalation gas line section 21 upstream of the exhalation valve 25 and downstream of the main pump 27. Inhalation gas is sent in the exhalation valve 25, through which the main line 15 extends as well, to the breathing mask 20 and exhalation gas is sent away from the breathing mask 20 and into the area surrounding the medical device 12 via the exhalation valve 25. This is shown by two separate arrows in FIG. 1 for illustration. The exhalation valve 25 does, indeed, have a total gas line section 22, in which inhalation gas is sent during inhalation and expiration gas during exhalation.

[0052] The exhalation valve 25 shown in FIG. 1 further has a first heat and moisture exchanger filter 16. More precisely, the first heat and moisture exchanger filter 16 is integrated within the exhalation valve 25. The first heat and moisture exchanger filter 16 is a part of a sensor arrangement 10, which is in turn a part of the medical device 12. The sensor arrangement 10 has a sensor unit 11 for determining a carbon dioxide concentration in the measured gas as well as a branch line 14 for branching off the measured gas from the main line 15 of the medical device 12 and for sending the branched-off measured gas to the sensor unit 11. The sensor arrangement 10 has, in addition, the first heat and moisture exchanger filter 16 as well as a second heat and moisture exchanger filter 17 for filtering the branched-off measured gas. The second heat and moisture exchanger filter 17 is arranged upstream of the sensor unit 11 directly at the sensor unit 11 when viewed towards the flow direction of the branched-off and suctioned-off measured gas.

[0053] To suction the measured gas out of the main line 15 or the total gas line section 22, the sensor arrangement 10 has a fluid delivery unit 24 in the form of a piezo pump. The fluid delivery unit 24 is arranged downstream of the sensor unit 11. The first heat and moisture exchanger filter 16 is configured according to FIG. 1 directly at a hose line of the branch line 14. The branch line 14 is thus connected by means of the hose line to the exhalation valve 25 and it forms there a fluid connection to the first heat and moisture exchanger filter 16 and makes possible a fluid connection from the main line 15 through the first heat and moisture exchanger filter 16 to the sensor unit 11. The exhalation valve 25 has to this end a valve port 26 in the form of a Luer lock fitting for connecting the branch line 14 or the hose line.

[0054] The heat and moisture exchanger filters 16, 17 shown have a microporous plastic foam each for filtering the measured gas and for achieving the desired buffering or compensating function concerning the temperature and moisture differences occurring in the measured gas.

[0055] Especially the heat conductivity of the exhalation gas is measured in the sensor unit 11 to determine a carbon dioxide concentration in the measured gas. The measurement is carried out by a micro structured heating element on a thin membrane of the sensor unit. A thermophilic unit, which measures an excess temperature of the gas close to the heating element in reference to a silicone frame of the membrane, is located next to the heating element. Further details in this connection can be found in the German patent application DE 10 2010 047 159 A1.

[0056] FIG. 2 shows a medical device according to a second embodiment. The exhalation valve 25 shown in FIG. 2 is shown at a spaced location from the breathing mask 20. Nevertheless, the total gas line section 22 may be defined as being a part of the exhalation valve 25. According to the exemplary embodiment shown in FIG. 2, the first heat and moisture exchanger filter 16 is arranged outside of the exhalation valve 25 as well as outside of the total gas line section 22 and within a hose line of the branch line 14. A valve port 26 is formed at the hose line in this case. The branch line 14 shown in FIG. 2 has a main line-side end section 18 for connecting the branch line 14 to the main line 15 and a sensor-side end section 19 for connecting the branch line 14 to the sensor unit 11, wherein the first heat and moisture exchanger filter 16 is arranged at the main line-side end section 18 and the second heat and moisture exchanger filter 17 is arranged at the sensor-side end section 19. More precisely, the two heat and moisture exchanger filters 16, 17 are integrated each as respective hose inserts into the hose line of the branch line 14. The hose line has a length of about 100 cm in the example shown and consists of a PVC-coated silicone hose.

[0057] FIG. 3 shows a sensor arrangement 10, in which the first heat and moisture exchanger filter 16 is configured in the main line-side end section 18 of the branch line 14 in the form of a hose insert, wherein the branch line 14 and the hose line have, when viewed in the flow direction of the measured gas through the branch line 14, a larger internal diameter at an area of the heat and moisture exchanger filter 16 than in an area downstream of the heat and moisture exchanger filter 16. More precisely, the internal diameter of the branch line 14 has a value of 3 mm at an area of the first heat and moisture exchanger filter 16 and the internal diameter of the branch line 14 downstream of the first heat and moisture exchanger filter 16 has a value of 1 mm. In the sensor arrangement 10 shown in FIG. 3, the branch line 14 and the hose line have the same internal diameter and the same external diameter each upstream of the first heat and moisture exchanger filter 16 as well as in the area of the first heat and moisture exchanger filter 16. The branch line 14 thus has, when viewed in the flow direction of the measured gas through the branch line 14, a larger internal diameter in the area upstream of the first heat and moisture exchanger filter 16 than downstream of the first heat and moisture exchanger filter 16. The internal diameter is always defined here as a diameter of a passage volume for sending the measured gas.

[0058] Even though the branch line 14 also has, when viewed in the flow direction of the measured gas through the branch line 14, a larger internal diameter in the area upstream of the first heat and moisture exchanger filter 16 than downstream of the first heat and moisture exchanger filter 16 in the exemplary embodiment shown in FIG. 4, the internal diameter as well as the external diameter of the branch line are larger in the area of the first heat and moisture exchanger filter 16 than upstream of the first heat and moisture exchanger filter 16. More precisely, the internal diameter of the branch line 14 has a value of 2 mm upstream of the first heat and moisture exchanger filter 16, the internal diameter of the branch line 14 at an area of the first heat and moisture exchanger filter 16 has a value of 3 mm, and the internal diameter of the branch line 14 downstream of the first heat and moisture exchanger filter 16 has a value of 1 mm. The length of the cylindrically configured, first heat and moisture exchanger filter has a value of 13 mm and the diameter has a value of 3 mm.

[0059] The first heat and moisture exchanger filter 16 and the second heat and moisture exchanger filter 17 are configured each at or outside of the hose line rather than within the hose line in the embodiment variant of the sensor arrangement 10 shown in FIG. 5. The branch line may be defined as a component arrangement which comprises the two heat and moisture exchanger filters 16, 17 as well as the hose line between the two heat and moisture exchanger filters 16, 17.

[0060] FIG. 6 shows a medical device 12 according to a third embodiment. According to this embodiment, the first heat and moisture exchanger filter 16 is located in the branch line 14 and within the total gas line section 22 and within a passage volume of the total gas line section 22. In addition, the branch line 14 extends within the main line 15 from the total gas line section 22 into the inhalation gas line section 21. In other words, the branch line 14 is guided coaxially or essentially coaxially partially within the main line 15 with reference to a longitudinal or extension direction of the branch line 14 and is enclosed by the main line in a jacket-like manner, especially over multiples of 10 cm.

[0061] FIG. 7 shows a medical device 12 in the form of a closed-circuit ventilator with an exhalation valve 25 and with an inhalation valve 29. The branch line 14 is connected according to FIG. 7 at a total gas line section 22 between a Y-section and the breathing mask 20. The medical device 12 shown in FIG. 7 has a control device 30 for actuating the fluid delivery unit 24 as well as the main pump 27. Further, a heat and moisture exchanger filter 28 of this class, which is several times larger than the heat and moisture exchanger filters 16, 17 of the sensor arrangement 10, is arranged downstream of the inhalation valve 29.

[0062] The manner of functioning of the heat and moisture exchanger filter 16 used now as a novel component will subsequently be explained with reference to FIGS. 8 through 10. The heat conduction of a gas depends on the components of the gas. Since oxygen and nitrogen have similar heat conductivities, the components with high concentrations are compensated. Depending on the setting of the medical device, the oxygen content in the inhalation gas varies, for example, from 21 vol. % in air to 100 vol. % during the use of pure oxygen. The rest is always nitrogen. Noble gases such as argon account for barely 1 vol. %. The exhaled gas stream additionally contains carbon dioxide, which is added by the gas exchange in the lungs. The oxygen content drops in the exhalation gas correspondingly. Healthy people inhale a gas containing about 4 vol. % to 5 vol. % of carbon dioxide. The percentage of oxygen is correspondingly about 16 vol. % to 95 vol. %. The percentage of noble gases remains constant. If the heat conduction is measured now continuously, the same gas mixture can be measured during the phase of exhalation as during the phase of inhalation, and the carbon dioxide will additionally appear during the phase of exhalation. An intentionally increased percentage of noble gases, such as with helium, for a reduced viscosity, is also irrelevant for the changes in relation to the phases of breathing. It can therefore be stated in a simplified manner that only the change in the heat conductivity must be measured during the breathing phases. The basic heat conduction proper plays no role. However, the added problem is that the exhalation gas will have been heated by the lungs to a temperature of about 36° C. and it has a relative humidity close to 100% at 36° C. The inhalation gas or inhaled air varies greatly depending on its source and may range from very dry in case of supply from a pressurized cylinder to very humid in case of the use of a blower with room air and humidifier. The temperature of the inhalation gas may likewise be subject to great variations depending on the climatic conditions.

[0063] Since the measurement by the sensor unit for measuring the carbon dioxide concentration is subject to a continual change between inhalation phase and exhalation phase, only the change of the measured values is preferably taken into account. The respective gas of the two phases of breathing is compensated in respect to moisture and temperature due to the proposed use of at least the first heat and moisture exchanger filter 16, through which flow of exhalation gas and inhalation gas always takes place alternatingly from both phases of breathing. So much heat and moisture exchanger filter material is preferably used or at least the first heat and moisture exchanger filter 16 is dimensioned such that no change or only a slight change in the signal due to temperature and moisture can be observed during the slowest breathing cycles of the person 13. The mean moisture content becomes established depending on the ventilation situation or the climatic situation. Different scenarios are shown in the table below.

TABLE-US-00001 Inhalation Exhalation Sensor (+7K) Temp. Rel. H.sub.2O Abs. H.sub.2O Temp. Rel. H.sub.2O Abs. H.sub.2O Temp. Rel. H.sub.2O Scenario [° C.} [mg/L] [mg/L] [° C.] [% rH] [mg/L] [° C.] [% rH] Room 23 40 8.22 30 100 30.35 30 63.5 Cylinder 23 0 0 30 100 30.35 30 49.5 Room 3 40 2.38 20 100 17.28 10 104 Room 23 90 18.5 30 100 30.35 30 80.5

[0064] The above table shows that the condensation may be critical under cold ambient conditions. The first heat and moisture exchanger filter 16, which is responsible for mixing the absolute moisture contents, is therefore installed and/or positioned as close to the main line 15 as possible, i.e., in an area that is located close to the ambient temperatures and therefore does not possibly allow high absolute moisture contents.

[0065] FIG. 8 shows the curve of a typical ventilation, during which the ventilation pressure is plotted over time. FIG. 9 shows a comparison between measured values for a medical device 12 in the form of a ventilator with the heat and moisture exchanger filter 16 being proposed (bottom) and without heat and moisture exchanger filter (top). Accordingly, FIG. 9 shows especially the buffering or the compensation of the differences in moisture, which would occur without a heat and moisture exchanger filter 16.

[0066] FIG. 10 shows a diagram in which a change in voltage is plotted over time. The carbon dioxide content can be inferred from the change in the voltage. It is accordingly important to obtain the most accurate voltage curve possible. If moist and warm gas is suctioned from the main line 15 to the sensor unit 11 without a heat and moisture exchanger filter 16, the heat conduction shows negative changes according to the lower, dotted line, because the heat conduction becomes better. The effect can be derived approximately from the moisture differences shown in FIG. 9. The effect would be superimposed now to the positive change according to the solid line at the top of FIG. 10, which develops due to the addition of 5 vol. % of carbon dioxide to the exhalation gas. Since the moisture and temperature difference is not predictable during the operation under unknown climatic conditions, there would be an uncertainty of about 10% in this case. The uncertainty would be even greater in case of very cool temperatures and/or of an especially dry gas. The temperature- and moisture-related voltage change can be compensated now according to the dash-dotted graphs shown in the center with the use of the heat and moisture exchanger filter 16 being proposed. Consequently, the influencing of the voltage measurement concerning the change in the carbon dioxide level between the inhalation gas and the exhalation gas can be reduced and the measurement result can be correspondingly improved.

[0067] The present invention allows additional configuration principles in addition to the embodiments shown. In other words, the present invention shall not be considered to be limited to the exemplary embodiments explained with reference to the figures. While specific embodiments of the invention have been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles.

LIST OF REFERENCE NUMBERS

[0068] 10 Sensor arrangement (array) [0069] 11 Sensor unit [0070] 12 Medical device [0071] 13 Person [0072] 14 Branch line [0073] 15 Main line [0074] 16 Heat and moisture exchanger filter [0075] 17 Heat and moisture exchanger filter [0076] 18 Main line-side end section [0077] 19 Sensor-side end section [0078] 20 Breathing mask [0079] 21 Inhalation gas line section [0080] 22 Total gas line section [0081] 23 Exhalation gas line section [0082] 24 Fluid delivery unit [0083] 25 Exhalation valve [0084] 26 Valve port [0085] 27 Main pump [0086] 28 Heat and moisture exchanger filter [0087] 29 Inhalation valve [0088] 30 Control device