Signal Quality Determination and Signal Correction System and Methods

• US 20080161710A1
• Filed: 12/17/2007
• Published: 07/03/2008
• Est. Priority Date: 12/21/2006
• Status: Active Grant

• Current Assignee: Philips RS North America LLC (Koninklijke Philips N.V.)
• Original Assignee: RIC INVESTMENTS LLC (Respironics Incorporated)
• Inventors: Gunneson, Paul B., Pierry, Anthony T.
• Granted Patent: US 8,357,099 B2
• Time in Patent Office: Days
• US Class Current: 600/532
• CPC Class Codes: A61B 5/083 Measuring rate of metabolism by using breath test, e.g. measuring rate of oxygen consumption
• CPC Class Codes: A61B 5/0836 Measuring rate of CO2 production
• CPC Class Codes: A61M 16/021 operated by electrical means A61M16/202 – A61M16/205 take precedence
• CPC Class Codes: A61M 16/0816 Joints or connectors
• CPC Class Codes: A61M 16/0833 T- or Y-type connectors, e.g. Y-piece
• CPC Class Codes: A61M 16/0858 Pressure sampling ports
• CPC Class Codes: A61M 2016/0027 pressure meter
• CPC Class Codes: A61M 2016/0036 in the breathing tube and used in both inspiratory and expiratory phase
• CPC Class Codes: A61M 2016/1025 the O2 concentration
• CPC Class Codes: A61M 2016/103 the CO2 concentration
• CPC Class Codes: A61M 2230/432 partial CO2 pressure (P-CO2)
• CPC Class Codes: A61M 2230/435 partial O2 pressure (P-O2)

Abstract

A mainstream gas monitoring system and method that includes using a mainstream airway adapter and a gas sensing assembly associated with the airway adapter to measure an analyte of a gas flow through the adapter. A gas sensing portion outputs a signal indicative of the analyte in a gas flow in the mainstream airway adapter. A processing portion receives the signal from the gas sensing portion and determines an amount of the analyte in the gas flow based on the signal from the gas sensing portion. The processing portion determines whether the oxygen measurements are of sufficient quality for their intended use, such as for measuring oxygen consumption or metabolic estimations. Quality measurements may be used to improve accuracy of derived metabolic estimations. Methods are provided by which carbon dioxide measurements can be processed and substituted for direct oxygen measurement for all or part of a respiratory cycle.

Claims

1. A system for measuring respiratory gases, comprising:

a first gas sensor constructed and arranged to measure an amount of a first gas;

a second gas sensor constructed and arranged to measure an amount of a second gas; and

a processor operatively connected with the first gas sensor and the second gas sensor, the processor receiving a first signal from the first gas sensor and a second signal from the second gas sensor, the processor adjusting the measured amount of the first gas based upon the measured amount of the second gas.

2. The system of claim 1, wherein the adjusting is based on (a) an inverted representation of the second signal, (b) scaled versions of the first and second signals, or (c) a scaled representation of the second signal.

3. The system of claim 1, wherein the processor calculates a measure of quality of the first signal based on a comparison of the first signal with the second signal the measure of quality being calculated using curve-fitting of the first signal to the second signal.

4. The system of claim 1, wherein the first signal and the second signal represent measurements of the first gas and the second gas, respectively.

5. The system of claim 1, wherein the first gas sensor is a luminescent quenching sensor.

6. The system of claim 5, wherein the luminescent quenching sensor is constructed and arranged to measure oxygen or carbon dioxide.

7. The system of claim 1, wherein the first gas sensor measures inspired oxygen and expired oxygen, and wherein the processor outputs a waveform representative of the adjusted measured amount of the inspired oxygen, expired oxygen, or both the inspired oxygen and the expired oxygen.

8. The system of claim 1, wherein the second gas sensor is an infrared sensor.

9. The system of claim 8, wherein the infrared sensor measures CO₂.

10. The system of claim 1, wherein the second gas sensor measures the amount of expired second gas only, and does not measure the amount of inspired second gas.

11. The system of claim 10, wherein the second gas is CO₂, and wherein the amount of inspired CO₂ is assumed to be zero.

12. The system of claim 1, wherein the second gas sensor measures both the amount of expired second gas and the amount of inspired second gas.

13. The system of claim 1, wherein the amount of the first respired gas and the amount of the second respired gas are measured as partial pressures of gas, or wherein the amount of the first respired gas and the amount of the second respired gas is measured as percentages of gas.

14. The system of claim 1, wherein the processor calculates a measure of quality of the first signal based on a comparison of the first signal with the second signal, wherein the processor is configured to substitute a portion of a reference signal for the first signal when the measure of quality falls below a predetermined minimum quality threshold, and wherein the reference signal is derived from the second signal.

15. The system of claim 14, wherein the reference signal is a scaled inverted version of the second signal.

16. The system of claim 1, wherein the processor calculates a measure of quality of the first signal based on a comparison of the first signal with the second signal and wherein the processor is configured to scale the first signal to compensate for a change in the measure of quality.

17. A system for measuring respiratory gases, comprising:

a first gas sensor that measures an amount of inspired and expired oxygen;

a second gas sensor that measures at least an amount of expired CO₂; and

a processor operatively connected with the first gas sensor and the second gas sensor, wherein the processor receives signals from the first gas sensor and from the second gas sensor and adjusts the measured amount of oxygen based upon the measured amount of CO₂.

18. The system of claim 17, wherein the measured amount of oxygen is adjusted by an amount related to measured quality of a signal received from the first gas sensor.

19. The system of claim 18, wherein the quality is measured by curve-fitting signals representative of the signals received by the processor.

20. The system of claim 19, wherein one of the representative signals is a scaled inverted version of a signal received from the second gas sensor.

21. The system of claim 17, wherein the measured amount of inspired and expired oxygen is estimated from the measured amount of expired CO₂ responsive to the measured quality falling below a predetermined level.

22. A method for measuring respiratory gases, comprising:

measuring an amount of a first gas;

measuring an amount of a second gas;

determining that the measured amount of the first gas requires adjustment; and

adjusting the measured amount of the first respired gas based upon the measured amount of the second gas.

23. The method of claim 22, wherein the step of determining includes comparing a first signal representative of the amount of the first gas and a second signal representative of the second gas, wherein the second signal is an inverted scaled version of a signal provided by a CO₂ sensor.

24. The method of claim 23, wherein the step of determining further includes curve fitting the first signal and the second signal to obtain a quality measurement of the first signal, wherein the measured amount of the first gas is adjusted in proportion to the quality measurement.

25. The method of claim 24, wherein the step of adjusting includes replacing the measured amount of the first gas with an estimate derived from the measured amount of the second gas.

26. The method of claim 22, wherein the first respired gas is measured using a luminescent quenching sensor.

27. The method of claim 26, wherein the luminescent quenching sensor is constructed and arranged to measure oxygen or carbon dioxide.

28. The method of claim 26, wherein the second respired gas is measured using an infrared sensor.

29. The method of claim 28, wherein the infrared sensor measures carbon dioxide.

30. The method of claim 22, wherein the second gas is measured as the amount of expired second gas only.

31. The method of claim 30, wherein the second gas is CO₂, and wherein the amount of inspired CO₂ is assumed to be zero.

32. The method of claim 22, wherein the second gas is measured as both the amount of expired second gas and the amount of inspired second gas.

33. The method of claim 22, wherein the amount of the first gas and the amount of the second gas are measured as partial pressures of gas, or wherein the amount of the first gas and the amount of the second gas are measured as percentages of gas.

34. A system for measuring respiratory gases, comprising:

means for measuring an amount of a first gas;

means for measuring an amount of a second gas; and

means for adjusting a measured amount of the first gas based upon a measured amount of the second gas.

35. The system of claim 34, wherein the adjusting is based on a comparison of a first signal representative of the amount of the first gas and a second signal representative of the amount of the second gas.

36. The system of claim 34, wherein the comparison is based on (a) an inverted version of the second signal, (b) scaled versions of the first and second signals, or (c) a scaled, inverted version of the second signal.

37. The system of claim 34, and further comprising means for calculating a measure of quality of a first signal representative of the amount of the first gas and a second signal representative of the amount of the second gas.

38. The system of claim 34, wherein the first signal is provided by a luminescent quenching sensor.

39. The system of claim 38, wherein the luminescent quenching sensor measures oxygen or carbon dioxide.

40. The system of claim 39, further comprising means for producing a waveform representative of an adjusted measured amount of inspired and expired oxygen, wherein the luminescent quenching sensor measures the inspired oxygen and the expired oxygen.

41. The system of claim 34, wherein the second signal is provided by an infrared sensor.

42. The system of claim 41, wherein the infrared sensor measures carbon dioxide.

43. The system of claim 34, wherein the second signal represents an amount of expired second gas only.

44. The system according to claim 43, wherein the second gas is carbon dioxide, and wherein the amount of inspired carbon dioxide is approximated as zero.

45. The system of claim 44, further comprising means for substituting a portion of a reference signal for the first signal responsive to the measure of quality falls below a predetermined minimum quality threshold, and wherein the reference signal is derived from the second signal.

46. The system of claim 34, and further comprising means for scaling a portion of the first signal to compensate for a change in the measure of quality.