Method of respiratory gas analysis using a metabolic calorimeter

• US 6,899,684 B2
• Filed: 06/10/2002
• Issued: 05/31/2005
• Est. Priority Date: 08/02/1999
• Status: Expired due to Term

• Current Assignee: Microlife Medical Home Solutions Inc.
• Original Assignee: HealtheTech, Inc.
• Inventors: Lawrence, Craig M., Prachar, Timothy J., Mault, James R., Weintraub, Jeffrey C., Nason, Kevin S., Barber, Theodore W., Pearce, Edwin M. Jr.
• Primary Examiner(s): Nasser, Robert L.
• Assistant Examiner(s): Mallari, Patricia
• Application Number:
  US10/167,349
• Publication Number:
  US 20030065274A1
• Time in Patent Office: 1,086 Days
• Field of Search: 600529-543, 600300-301, 73/233
• US Class Current: 600/531
• CPC Class Codes: A61B 5/0002 Remote monitoring of patients using telemetry, e.g. transmission of vital signals via a communication network A61B5/07 takes precedence; transmission systems for measured values G08C; transmission H04B; transmission of digital information H04L; wireless communication networks H04W
• CPC Class Codes: A61B 5/02438 with portable devices, e.g. worn by the patient
• CPC Class Codes: A61B 5/0833 Measuring rate of oxygen consumption
• CPC Class Codes: A61B 5/087 Measuring breath flow
• CPC Class Codes: A61B 5/091 Measuring volume of inspired or expired gases, e.g. to determine lung capacity
• CPC Class Codes: A61B 5/222 combined with detection or measurement of physiological parameters, e.g. heart rate
• CPC Class Codes: G01N 33/497 of gaseous biological material, e.g. breath

Abstract

A method of determining a respiratory parameter for a subject using an indirect calorimeter is provided. The indirect calorimeter includes a respiratory connector for passing inhaled and exhaled gases, a flow pathway operable to receive and pass inhaled and exhaled gases having a flow tube within the flow pathway through which the inhaled and exhaled gases pass, a flow meter for determining an instantaneous flow volume of the inhaled and exhaled gases, a component gas concentration sensor for determining an instantaneous fraction of a predetermined component gas and a computation unit having a processor and a memory. The method includes the steps of initializing the indirect calorimeter and the subject breathing into the respiratory connector if the indirect calorimeter is initialized, sensing the flow volume of the inhaled and exhaled gases passing through the flow pathway using the flow meter and transmitting a signal representing the sensed flow volume to the computation unit. The method also includes the steps of sensing a concentration of a predetermined component gas as the inhaled and exhaled gases pass through the flow pathway using the component gas sensor, and transmitting a signal representing the sensed concentration of the predetermined component gas to the computation unit. The method further includes the steps of calculating at least one respiratory parameter for the subject as the subject breathes through the calorimeter using the sensed flow volume and the sensed concentration of the predetermined component gas, and providing the subject with the at least one respiratory parameter.

Claims

1. A method of determining a respiratory parameter for a subject using an indirect calorimeter, comprising:

initializing the indirect calorimeter, wherein the indirect calorimeter includes a respiratory connector for passing inhaled and exhaled gases as the subject breathes, a flow pathway operable to receive and pass the inhaled and exhaled gases and having a flow tube within the flow pathway through which the inhaled and exhaled gases pass, a flow meter, a component gas concentration sensor, and a computation unit having a processor and a memory;

passing the inhaled and exhaled gases through the respiratory connector, if the indirect calorimeter is initialized;

sensing a flow volume of the inhaled and exhaled gases passing through the flow pathway, using the flow meter, and transmitting a signal representing the sensed flow volume to the computation unit;

sensing a concentration of a predetermined component gas in at least one of the inhaled and exhaled gases passing through the flow pathway, using the component gas concentration sensor, and transmitting a signal representing the sensed concentration to the computation unit;

determining if the subject'"'"'s breathing has reached steady state;

calculating at least one respiratory parameter for the subject at steady state using the sensed flow volume and the sensed concentration; and

providing the at least one respiratory parameter to the subject.

2. The method as set forth in claim 1, wherein the predetermined component gas is oxygen, and the component gas concentration sensor is an oxygen sensor.

3. The method as set forth in claim 2, wherein the oxygen sensor is a fluorescence quench type oxygen sensor.

4. The method as set forth in claim 2, wherein initializing the indirect calorimeter includes heating the oxygen sensor to a predetermined temperature in order to sense a concentration of oxygen in at least one of the inhaled and exhaled gases.

5. The method as set forth in claim 1, wherein initializing the indirect calorimeter includes initializing the flow meter by determining if there is zero flow through the flow meter and zeroing the flow meter if a flow is indicated.

6. The method as set forth in claim 1, wherein the respiratory connector is a mask.

7. The method as set forth in claim 1, wherein determining if the subject'"'"'s breathing has reached steady state includes:

determining an amount of oxygen consumed by the subject using the sensed flow volume and the sensed concentration; and

determining if the amount of oxygen consumed has reached steady state.

8. The method as set forth in claim 7, further including estimating a steady state amount of oxygen consumed if the subject'"'"'s breathing does not reach steady state.

9. The method as set forth in claim 7, further including notifying the subject if the subject'"'"'s breathing does not reach steady state.

10. The method as set forth in claim 7, further including waiting a predetermined period of time after detecting a flow of the inhaled and exhaled gases before determining if the subject'"'"'s breathing has reached steady state.

11. The method as set forth in claim 1, wherein providing the at least one respiratory parameter includes displaying the at least one respiratory parameter on a display screen of the indirect calorimeter.

12. The method as set forth in claim 1, wherein the computation unit is operatively connected to a removable data storage device.

13. The method as set forth in claim 1, wherein providing the at least one respiratory parameter includes communicating with a remote computing device via a communication network.

14. The method as set forth in claim 13, wherein the communication network is a wireless communication network.

15. The method as set forth in claim 1, wherein the at least one respiratory parameter is a resting metabolic rate, which is calculated from an amount of oxygen consumed by the subject and an amount of carbon dioxide produced by the subject.

16. The method as set forth in claim 15, further including determining the amount of oxygen consumed and the amount of carbon dioxide produced using the sensed flow volume and the sensed concentration.

17. The method as set forth in claim 16, wherein the component gas concentration sensor is a combined fluorescent quench sensor for sensing a concentration of carbon dioxide and a concentration of oxygen in at least one of the inhaled and exhaled gases.

18. The method as set forth in claim 16, further including determining a respiratory quotient using the amount of oxygen consumed and the amount of carbon dioxide produced.

19. The method as set forth in claim 16, further including determining the subject'"'"'s rate of oxygen consumption from the sensed flow volume and the sensed concentration.

20. The method as set forth in claim 15, wherein calculating the resting metabolic rate includes sensing a temperature using a temperature sensing means, sensing a pressure using a pressure sensing means, sensing a humidity using a humidity sensing means, and using the sensed temperature, the sensed pressure, and the sensed humidity in calculating the resting metabolic rate.

21. The method as set forth in claim 1, wherein the flow meter is an ultrasonic transducer.

22. The method as set forth in claim 21, wherein the flow meter includes an upper ultrasonic transducer and a lower ultrasonic transducer, each in fluid communication with the inhaled and exhaled gases passing through the flow pathway.

23. The method as set forth in claim 21, wherein the ultrasonic transducer includes a plurality of microscopic transducers arranged in an array.

24. The method as set forth in claim 23, wherein the microscopic transducers measure a temperature, a pressure, and a humidity for correcting the sensed flow volume due to effects of temperature, pressure, and humidity.

25. The method as set forth in claim 1, wherein the flow pathway includes a first end in fluid communication with the respiratory connector and a second end in fluid communication with a source and sink for respiratory gases, and the flow pathway includes an outer housing surrounding the flow tube and a chamber disposed between the flow tube and the first end, such that the chamber is a concentric chamber surrounding one end of the flow tube and being defined between the flow tube and the outer housing.

26. A method of determining a respiratory parameter for a subject using an indirect calorimeter, comprising:

initializing the indirect calorimeter, wherein the indirect calorimeter includes a respiratory connector for passing inhaled and exhaled gases as the subject breathes, a flow pathway operable to receive and pass the inhaled and exhaled gases and having a flow tube within the flow pathway through which the inhaled and exhaled gases pass, a flow meter, a component gas concentration sensor, and a computation unit having a processor and a memory;

passing the inhaled and exhaled gases through the respiratory connector after the indirect calorimeter is initialized;

sensing an instantaneous flow volume of the inhaled and exhaled gases passing through the flow pathway, using the flow meter, and transmitting a signal representing the sensed instantaneous flow volume to the computation unit;

sensing an instantaneous concentration of a predetermined component gas in at least one of the inhaled and exhaled gases passing through the flow pathway, using the component gas concentration sensor, and transmitting a signal representing the sensed instantaneous concentration to the computation unit;

calculating an instantaneous metabolic rate for the subject as the subject breathes through the indirect calorimeter using the sensed instantaneous flow volume and the sensed instantaneous concentration;

determining if the instantaneous metabolic rate has reached steady state;

determining a resting metabolic rate if the instantaneous metabolic rate has reached steady state; and

providing the resting metabolic rate to the subject.

27. The method as set forth in claim 26, wherein the flow pathway includes a first end in fluid communication with the respiratory connector and a second end in fluid communication with a source and sink for respiratory gases, and the flow pathway includes an outer housing surrounding the flow tube and a chamber disposed between the flow tube and the first end, such that the chamber is a concentric chamber surrounding one end of the flow tube and being defined between the flow tube and the outer housing.

28. The method as set forth in claim 26, wherein the respiratory connector is a mask.

29. The method as set forth in claim 26, wherein the predetermined component gas is oxygen, and the component gas concentration sensor is an oxygen sensor.

30. The method as set forth in claim 29, wherein the oxygen sensor is a fluorescence quench type oxygen sensor.

31. The method as set forth in claim 29, wherein initializing the indirect calorimeter includes heating the oxygen sensor to a predetermined temperature in order to sense an instantaneous concentration of oxygen in at least one of the inhaled and exhaled gases.

32. The method as set forth in claim 26, wherein initializing the indirect calorimeter includes initializing the flow meter by determining if there is zero flow through the flow meter and zeroing the flow meter if a flow is indicated.

33. The method as set forth in claim 26, wherein determining if the instantaneous metabolic rate has reached steady state includes:

determining an amount of oxygen consumed by the subject using the sensed instantaneous flow volume and the sensed instantaneous concentration; and

determining if the amount of oxygen consumed has reached steady state.

34. The method as set forth in claim 33, further including estimating a steady state amount of oxygen consumed if the subject'"'"'s breathing does not reach steady state.

35. The method as set forth in claim 33, further including notifying the subject if the subject'"'"'s breathing does not reach steady state.

36. The method as set forth in claim 33, further including waiting a predetermined period of time after detecting a flow of the inhaled and exhaled gases before determining if the instantaneous metabolic rate has reached steady state.

37. The method as set forth in claim 26, wherein providing the resting metabolic rate includes displaying the resting metabolic rate on a display screen of the indirect calorimeter.

38. The method as set forth in claim 26, wherein providing the resting metabolic rate includes transmitting the resting metabolic rate to another electronic device via a communication network.

39. The method as set forth in claim 38, wherein the communication network is a wireless communication network.

40. The method as set forth in claim 26, wherein the computation unit is operatively connected to a removable data storage device.

41. The method as set forth in claim 26, wherein the resting metabolic rate is determined from an amount of oxygen consumed by the subject and an amount of carbon dioxide produced by the subject.

42. The method as set forth in claim 41, further including determining the amount of oxygen consumed and the amount of carbon dioxide produced using the sensed instantaneous flow volume and the sensed instantaneous concentration.

43. The method as set forth in claim 42, wherein the component gas concentration sensor is a combined fluorescent quench sensor for sensing an instantaneous concentration of carbon dioxide and an instantaneous concentration of oxygen in at least one of the inhaled and exhaled gases.

44. The method as set forth in claim 42, further including determining a respiratory quotient using the amount of oxygen consumed and the amount of carbon dioxide produced.

45. The method as set forth in claim 42, further including determining the subject'"'"'s rate of oxygen consumption from the sensed instantaneous flow volume and the sensed instantaneous concentration.

46. The method as set forth in claim 26, wherein calculating the instantaneous metabolic rate includes sensing a temperature using a temperature sensing means, sensing a pressure using a pressure sensing means, sensing a humidity using a humidity sensing means, and using the sensed temperature, the sensed pressure, and the sensed humidity in calculating the instantaneous metabolic rate.

47. The method as set forth in claim 26, wherein the flow meter is an ultrasonic transducer.

48. The method as set forth in claim 47, wherein the flow meter includes an upper ultrasonic transducer and a lower ultrasonic transducer, each in fluid communication with the inhaled and exhaled gases passing through the flow pathway.

49. The method as set forth in claim 47, wherein the ultrasonic transducer includes a plurality of microscopic transducers arranged in an array.

50. The method as set forth in claim 49, wherein the microscopic transducers measure a temperature, a pressure, and a humidity for correcting the sensed instantaneous flow volume due to effects of temperature, pressure, and humidity.

51. A method of determining a respiratory parameter for a subject using an indirect calorimeter, comprising:

initializing the indirect calorimeter, wherein the indirect calorimeter includes a respiratory connector for passing inhaled and exhaled gases as the subject breathes, a flow pathway operable to receive and pass the inhaled and exhaled gases and having a flow tube within the flow pathway through which the inhaled and exhaled gases pass, a flow meter, an oxygen sensor, a carbon dioxide sensor, and a computation unit having a processor and a memory;

passing the inhaled and exhaled gases through the respiratory connector, if the indirect calorimeter is initialized;

sensing a flow volume of the inhaled and exhaled gases passing through the flow pathway, using the flow meter, and transmitting a signal representing the sensed flow volume to the computation unit;

sensing a concentration of oxygen in at least one of the inhaled and exhaled gases passing through the flow pathway, using the oxygen sensor, and transmitting a signal representing the sensed concentration of oxygen to the computation unit;

sensing a concentration of carbon dioxide in at least one of the inhaled and exhaled gases passing through the flow pathway, using the carbon dioxide sensor, and transmitting a signal representing the sensed concentration of carbon dioxide to the computation unit;

calculating at least one respiratory parameter for the subject as the subject breathes through the indirect calorimeter using the sensed flow volume, the sensed concentration of oxygen, and the sensed concentration of carbon dioxide;

determining if the subject'"'"'s breathing has reached steady state; and

providing the at least one respiratory parameter to the subject after the subject'"'"'s breathing has reached steady state.

52. The method as set forth in claim 51, wherein the flow meter includes an upper ultrasonic transducer and a lower ultrasonic transducer, each in fluid communication with the inhaled and exhaled gases passing through the flow pathway.

53. The method as set forth in claim 51, wherein the flow meter includes a plurality of microscopic transducers arranged in an array.

54. The method as set forth in claim 53, wherein the microscopic transducers measure a temperature, a pressure, and a humidity for correcting the sensed flow volume due to effects of temperature, pressure, and humidity.

55. The method as set forth in claim 51, wherein the oxygen sensor is a fluorescence quench type oxygen sensor.

56. The method as set forth in claim 51, wherein initializing the indirect calorimeter includes heating the oxygen sensor to a predetermined temperature in order to sense the concentration of oxygen in at least one of the inhaled and exhaled gases.

57. The method as set forth in claim 51, wherein determining if the subject'"'"'s breathing has reached steady state includes:

determining an amount of oxygen consumed by the subject using the sensed flow volume and the sensed concentration of oxygen; and

determining if the amount of oxygen consumed has reached steady state.

58. The method as set forth in claim 57, further including estimating a steady state amount of oxygen consumed if the subject'"'"'s breathing does not reach steady state.

59. The method as set forth in claim 57, further including notifying the subject if the subject'"'"'s breathing does not reach steady state.

60. The method as set forth in claim 51, wherein calculating the at least one respiratory parameter includes calculating a resting metabolic rate using the sensed flow volume, the sensed concentration of oxygen, and the sensed concentration of carbon dioxide.

61. The method as set forth in claim 60, wherein calculating the resting metabolic rate includes sensing a temperature using a temperature sensing means, sensing a pressure using a pressure sensing means, sensing a humidity using a humidity sensing means, and using the sensed temperature, the sensed pressure, and the sensed humidity in calculating the resting metabolic rate.

62. The method as set forth in claim 51, wherein the oxygen sensor and the carbon dioxide sensor is a combined fluorescent quench sensor for sensing the concentration of carbon dioxide and the concentration of oxygen in at least one of the inhaled and exhaled gases.

63. The method as set forth in claim 51, wherein calculating the at least one respiratory parameter includes determining a respiratory quotient using the sensed flow volume, the sensed concentration of oxygen, and the sensed concentration of carbon dioxide.