Gas sensor

• US 20080262370A1
• Filed: 04/10/2008
• Published: 10/23/2008
• Est. Priority Date: 10/18/2006
• Status: Active Grant

• Current Assignee: Anaxsys Technology Limited
• Original Assignee: Anaxsys Technology Limited
• Inventors: Garrett, Michael, Williams, Deryk John Peter, Varney, Mark Sinclair
• Granted Patent: US 8,449,473 B2
• Time in Patent Office: Days
• US Class Current: 600/532
• CPC Class Codes: A61B 5/0836 Measuring rate of CO2 production

Abstract

A method of determining the respiratory function of a subject is disclosed, the method comprising measuring the concentration of water vapour in the gas stream exhaled by the subject, and from the measured water vapour concentration determining the respiratory function of the subject. Mathematical techniques for analyzing the data obtained from the measurement of concentrations of gaseous components in an exhaled gas stream are also disclosed and their use in determining the lung function of a subject.

Claims

1. A method of determining the respiratory function of a subject, the method comprising:

measuring the concentration of water vapour in the gas stream exhaled by the subject; and

from the measured water vapour concentration determining the respiratory function of the subject.

2. The method according to claim 1, wherein the concentration of water vapour is measured for the duration of at least one complete exhalation.

3. The method according to claim 2, wherein the concentration of water vapour is measured during tidal breathing by the subject.

4. The method according to claim 1, wherein the exhaled gas stream is exhaled from the mouth of the subject.

5. The method according to claim 1, wherein the water vapour content is measured using an electrochemical sensor.

6. The method of claim 5, comprising:

causing the gas stream to impinge on a sensing element comprising a working electrode and a counter electrode;

applying an electric potential across the working electrode and counter electrode;

measuring the current flowing between the working electrode and counter electrode as a result of the applied potential; and

determining from the measured current flow an indication of the concentration of the water vapour in the gas stream.

7. The method of claim 6, wherein a constant voltage is applied across the working electrode and the counter electrode.

8. The method of claim 6, wherein a variable voltage is applied across the working electrode and the counter electrode.

9. The method of claim 8, wherein the variable voltage alternates between a rest potential and a potential above the reaction threshold potential.

10. The method of claim 9, wherein the voltage is pulsed at a frequency of from 0.1 Hz to 20 kHz.

11. The method of claim 5, wherein the electrochemical sensor comprises a plurality of electrodes and a layer of ion-exchange material extending between the electrodes, the layer comprising particles of a mesoporous material dispersed therein.

12. The method of claim 11, wherein the dispersion of mesoporous material is a fine dispersion.

13. A method of determining the lung function of a subject, the method comprising:

measuring the change in concentration of a gaseous component of the exhaled gas stream of the subject;

determining the change in concentration as a function of time for the exhaled gas stream to obtain a profile of the change in concentration with time;

measuring the slope of the ascending phase of the profile; and

using the slope of the ascending phase making a determination of the lung function of the subject.

14. The method according to claim 13, wherein the gaseous component is selected from the group consisting of carbon dioxide and water vapour.

15. The method according to claim 13, further comprising measuring the slope of the plateau phase of the profile.

16. The method according to claim 15, wherein the ratio of the slope of the ascending phase and the plateau phase is determined.

17. A method of determining the lung function of a subject, the method comprising:

measuring the change in concentration of a gaseous component of the exhaled gas stream of the subject;

determining the change in concentration as a function of time for the exhaled gas stream to obtain a profile of the change in concentration with time;

analyzing the portion of the profile in the region of the transition from the ascending phase to the plateau phase; and

using the results of the analysis to make a determination of the lung function of the subject.

18. The method according to claim 17, wherein the analysis comprises applying regression techniques to the data of the profile.

19. The method according to claim 17, wherein the analysis comprises applying best fit techniques to the data of the profile.

20. The method according to claim 17, wherein the analysis comprises representing the portion of the profile in the region of the transition form the ascending phase to the plateau phase by equation 1:

$\begin{array}{cc}Y=\frac{1}{1+{\mathrm{aX}}^2}& \left(1\right)\end{array}$

where Y is the concentration of carbon dioxide and X is the time.

21. The method according to claim 20, wherein best fit analysis is applied to a plot of Y′

versus time, where Y′

is defined by equation 2;

Y′

=(1/(Y−

1))^1/2 

 

(2)

and the slope of the line so-obtained is determined to provide a value for coefficient a in equation 1.

22. The method according to claim 21, wherein the value of coefficient a is used to provide an indication of lung function.

23. The method according to claim 17, wherein the gaseous component is selected from the group consisting of carbon dioxide and water vapour.

24. A method for monitoring the lung function of a subject, the method comprising the steps of:

measuring the change in concentration of a gaseous component of the exhaled gas stream of the subject;

determining the change in concentration as a function of time for the exhaled gas stream to obtain a profile of the change in concentration with time;

comparing the profile thus obtained with a pre-existing profile; and

using the comparison in making a determination of the lung function of the subject.

25. The method according to claim 24, wherein the profile thus obtained is compared with a plurality of pre-existing profiles, to provide a pattern of changing lung function over time.

26. The method according to claim 24, wherein the pre-existing profile is a profile obtained from the subject.

27. The method according to claim 24, wherein the pre-existing profile is a profile representing normal lung function.

28. The method according to claim 24, wherein the gaseous component is selected from the group consisting of carbon dioxide and water.

29. A device for monitoring the lung function of a subject, the device comprising:

means for measuring the change in concentration of a gaseous component of the exhaled gas stream of the subject;

means determining the change in concentration as a function of time for the exhaled gas stream to obtain a profile of the change in concentration with time;

means for storing a plurality of profiles; and

means for comparing the profile thus obtained with a pre-existing profile retrieved from the storage means.

30. The device according to claim 29, wherein the means for storing a plurality of profiles is adapted to store a plurality of pre-existing profiles.

31. The device according to claim 29, wherein the means for comparing the profiles comprises display means for displaying a plurality of profiles for visual comparison by a user.

32. The device according to claim 29, wherein the means for comparing the profiles comprises means for performing mathematical analysis of a profile.

33. A method for the determination of the carbon dioxide content of an exhaled gas stream, the method comprising:

measuring the water vapour content of the exhaled gas stream; and

determining the concentration of carbon dioxide in the exhaled gas stream from the measured water vapour content.

34. The method according to claim 33, wherein the exhaled gas stream is exhaled from the mouth of the subject.

35. The method according to claim 33, wherein the water vapour content is measured using an electrochemical sensor.

36. The method according to claim 35 comprising:

causing the gas stream to impinge on a sensing element comprising a working electrode and a counter electrode;

applying an electric potential across the working electrode and counter electrode;

measuring the current flowing between the working electrode and counter electrode as a result of the applied potential; and

determining from the measured current flow an indication of the concentration of the water vapour in the gas stream.

37. The method according to claim 36, wherein a constant voltage is applied across the working electrode and the counter electrode.

38. The method according to claim 36, wherein a variable voltage is applied across the working electrode and the counter electrode.

39. The method according to claim 38, wherein the variable voltage alternates between a rest potential and a potential above the reaction threshold potential.

40. The method according to claim 39, wherein the voltage is pulsed at a frequency of from 0.1 Hz to 20 kHz.

42. The sensor according to claim 40, comprising:

a sensing element disposed to be exposed to the gas stream, the sensing element comprising;

a working electrode; and

a counter electrode.

43. The sensor according to claim 42, further comprising a conduit through which the gas stream is channeled to impinge upon the sensing element.

44. The sensor according to claim 43, wherein the conduit comprises a mouthpiece into which a patient may exhale.

45. The sensor according to claim 42, wherein the working electrode and counter electrode are in a form selected from a point, a line, rings and flat planar surfaces.

46. The sensor according to claim 42, wherein one or both of the working electrode and the counter electrode comprises a plurality of electrode portions.

47. The sensor according to claim 46, wherein both the working electrode and the counter electrode comprise a plurality of electrode portions arranged in an interlocking pattern.

48. The sensor according to claim 47, wherein the electrode portions are arranged in a concentric pattern.

49. The sensor according to claim 42, wherein the surface area of the counter electrode is greater than the surface area of the working electrode.

50. The sensor according to claim 49, wherein the ratio of the surface area of the counter electrode to the working electrode is at least 2:

1, more preferably at least 5;

1.

51. The sensor according to claim 42, wherein the electrodes are supported on an inert substrate.

52. The sensor according to claim 42, wherein each electrode comprises a metal selected from Group VIII of the Periodic Table of the Elements, copper, silver and gold, preferably gold or platinum.

53. The sensor according to claim 42, further comprising a layer of insulating material disposed over a portion of each electrode, the insulating layer being so shaped as to leave a portion of each electrode exposed for contact with a gas stream.

54. The sensor according to claim 42, further comprising a reference electrode.

55. The sensor according to claim 42, wherein the electrodes are mounted on a substrate, the electrodes being applied to the substrate by thick film screen printing, spin/sputter coating or visible/ultraviolet/laser photolithography.

56. The sensor according to claim 42, wherein one or more electrodes is comprised of a plurality of layers, the outer layer being a layer of pure metal applied by electrochemical plating.

41. A sensor for determining the concentration of carbon dioxide in an exhaled gas stream, the sensor comprising:

means for determining the concentration of water vapour in the exhaled gas stream; and

means for calculating the concentration of carbon dioxide in the exhaled gas stream from the measured water vapour concentration.

57. A system for monitoring the composition of a gas stream comprising:

a sensor according to claim 41;

a microcontroller for receiving an output from the sensor; and

a display;

wherein

the microcontroller is programmed to generate a continuous image of the concentration of carbon dioxide in the gas stream being analysed on the display.