Method of respiratory gas analysis using a metabolic calorimeter

• US 20030065274A1
• Filed: 06/10/2002
• Published: 04/03/2003
• Est. Priority Date: 08/02/1999
• Status: Active Grant

• Current Assignee: Microlife Medical Home Solutions Inc.
• Original Assignee: HealtheTech, Inc.
• Inventors: Nason, Kevin S., Lawrence, Craig M., Prachar, Timothy J., Mault, James R., Weintraub, Jeffrey C., Barber, Theodore W., Pearce, Edwin M. Jr.
• Granted Patent: US 6,899,684 B2
• Time in Patent Office: Days
• 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, said method comprising the steps of:

initializing the indirect calorimeter, wherein 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;

breathing into the respiratory connector for the indirect calorimeter by the subject, 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;

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;

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 at least one respiratory parameter to the subject.

2. The calorimeter according to claim 1, wherein the predetermined component gas is oxygen and the component gas concentration sensor is an oxygen sensor.

3. The calorimeter according to claim 2, wherein the oxygen sensor is a fluorescence quench type oxygen sensor.

4. The method as set forth in claim 2, wherein said step of initializing the indirect calorimeter includes the step of heating the oxygen sensor to a predetermined temperature in order to determine the fractional volume of oxygen in the inhaled and exhaled gases.

5. The method as set forth in claim 1, wherein said step of initializing the indirect calorimeter includes the step of 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, further including the step of determining if the subject'"'"'s breathing has reached a steady state and calculating the at least one respiratory parameter after the subject'"'"'s breathing has reached a steady state.

7. The method as set forth in claim 6, wherein said step of determining a steady state includes the steps of:

periodically measuring flow volume and component gas concentration of the inhaled and exhaled gases;

determining an average flow rate and component gas concentration for a predetermined period and using the average flow rate and component gas concentration to calculate an average volume of oxygen (VO₂);

comparing the average VO₂ for a predetermined number of consecutive periods to determine if the average VO₂ for each of the periods are within a predetermined steady state range; and

determining at least one respiratory parameter after VO₂ has attained a steady state.

8. The method as set forth in claim 7, further including the step of estimating a steady state VO₂ if the subject'"'"'s breathing does not reach a steady state.

9. The method as set forth in claim 6, further including the step of notifying the subject if the subject'"'"'s breathing does not reach a steady state.

10. The method as set forth in claim 6, further including the step of waiting a predetermined period of time after detecting a flow of inhaled and exhaled gases before determining if the instantaneous metabolic rate has reached a steady state.

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

12. The method as set forth in claim 1, wherein said step of providing the at least one respiratory parameter includes the step of communicating with a remote computing device via a communications network.

13. The method as set forth in claim 12 wherein the communications network is the Internet.

14. The method as set forth in claim 12 wherein the data is transferred using a Bluetooth wireless communications network.

15. The method as set forth in claim 1, wherein the respiratory parameter is resting metabolic rate, which is calculated from the volume of oxygen consumed (VO₂) by the subject and the volume of carbon dioxide produced (VCO₂) by the subject.

16. The method as set forth in claim 15, further including the step of determining VCO₂ in the exhaled gases using a carbon dioxide sensing means.

17. The method as set forth in claim 16, wherein said gas concentration sensor is a combined fluorescent quench sensor for measuring the concentration of carbon dioxide and the concentration of oxygen in the flow of inhaled and exhaled gases.

18. The method as set forth in claim 16, further including the step of determining a respiratory quotient using the sensed concentration of carbon dioxide in the exhaled gas.

19. The method as set forth in claim 15, further including the step of determining the subject'"'"'s rate of oxygen consumption from the flow volume and oxygen consumption.

20. The method as set forth in claim 15 wherein said step of calculating the metabolic rate also includes the step of sensing temperature using a temperature sensing means, sensing pressure using a pressure sensing means and sensing humidity using a humidity sensing means and using the sensed temperature, pressure and 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 calorimeter according to claim 22, 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 temperature, pressure and humidity for correcting the gas flow rate due to the corresponding 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 tube 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. The method as set forth in claim 1, wherein the respiratory connector is a mask.

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

28. A method of determining a respiratory parameter for a subject using an indirect calorimeter, said method comprising the steps of:

initializing the indirect calorimeter, wherein said 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 concentration of a predetermined component gas and a computation unit having a processor and a memory;

breathing into the respiratory connector for the indirect calorimeter by the subject after the indirect calorimeter is initialized;

sensing the 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 a fractional volume 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 instantaneous flow volume to the computation unit;

calculating an instantaneous metabolic rate for the subject as the subject breathes through the calorimeter using the sensed flow volume and the sensed concentration of the predetermined component gas;

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

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

providing the resting metabolic rate to the subject.

29. The calorimeter according to claim 28, wherein the predetermined component gas is oxygen and the component gas concentration sensor is an oxygen sensor.

30. The calorimeter according to claim 29, wherein the oxygen sensor is a fluorescence quench type oxygen sensor.

31. The method as set forth in claim 29, wherein said step of initializing the indirect calorimeter includes the step of heating the oxygen sensor to a predetermined temperature in order to determine the fractional volume of oxygen in the inhaled and exhaled gases.

32. The method as set forth in claim 28, wherein said step of initializing the indirect calorimeter includes the step of 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 28, wherein said step of determining if the instantaneous metabolic rate has reached a steady state includes the steps of:

periodically measuring flow volume and component gas concentration;

determining an average flow volume and component gas concentration for a predetermined period and using the average flow rate and component gas concentration to determine an average VO₂;

comparing the average VO₂ for a predetermined number of consecutive periods to determine if the average VO₂s for each of the periods are within a predetermined steady state range; and

determining the resting metabolic rate after VO₂ has attained a steady state.

34. The method as set forth in claim 33, further including the step of estimating a steady state VO₂ if the subject'"'"'s breathing does not reach a steady state.

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

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

37. The method as set forth in claim 28, wherein said step of providing the resting metabolic rate includes the step of displaying the resting metabolic rate on a display screen for the indirect calorimeter.

38. The method as set forth in claim 28, wherein said step of providing the resting metabolic rate includes the step of transmitting the resting metabolic rate to another electronic device via a communications network.

39. The method as set forth in claim 38, wherein the communications network is the Internet.

40. The method as set forth in claim 38, wherein said data is transferred using a Bluetooth wireless communications network.

41. The calorimeter according to claim 28, wherein the resting metabolic rate is calculated from the volume of oxygen consumed (VO₂) by the subject and the amount of carbon dioxide produced (VCO₂) by the subject.

42. The method as set forth in claim 41, further including the step of determining the VO₂ in the exhaled gases using a carbon dioxide sensing means.

43. The method as set forth in claim 42, wherein said gas concentration sensor is a combined fluorescent quench sensor for measuring the concentration of carbon dioxide and the concentration of oxygen in the flow of inhaled and exhaled gases.

44. The method as set forth in claim 42, further including the step of determining a respiratory quotient using the sensed concentration of carbon dioxide in the exhaled gas.

45. The method as set forth in claim 41, further including the step of determining the subject'"'"'s rate of oxygen consumption from the flow volume and oxygen consumption.

46. The method as set forth in claim 28, wherein said step of calculating the metabolic rate also includes the step of sensing temperature using a temperature sensing means, sensing pressure using a pressure sensing means and sensing humidity using a humidity sensing means and using the sensed temperature, pressure and humidity in calculating the resting metabolic rate.

47. The method as set forth in claim 28, 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 calorimeter according to claim 48, 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 temperature, pressure and humidity for correcting the gas flow rate due to the corresponding effects of temperature, pressure and humidity.

51. The method as set forth in claim 28, 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 tube 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.

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

53. The method as set forth in claim 28, wherein the computation unit is operatively connected to a removable data storage device.

54. A method of determining a respiratory parameter for a subject using an indirect calorimeter, said method comprising the steps of:

initializing the indirect calorimeter, wherein said 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;

breathing into the respiratory connector for the indirect calorimeter by the subject, if the indirect calorimeter is initialized;

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

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

sensing a concentration of a carbon dioxide in the inhaled and exhaled gases passing through the flow pathway using a 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 calorimeter using the sensed flow volume and the sensed volume of oxygen (VO₂) and carbon dioxide (VCO₂);

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

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

55. The calorimeter according to claim 54, wherein said oxygen sensor is a fluorescence quench type oxygen sensor.

56. The method as set forth in claim 54, wherein said step of initializing the indirect calorimeter includes the step of heating the oxygen sensor to a predetermined temperature in order to determine the fractional volume of oxygen in the inhaled and exhaled gases.

57. The method as set forth in claim 54, wherein said step of determining a steady state includes the steps of:

periodically measuring flow rate, oxygen concentration and carbon dioxide concentration;

determining an average flow rate, oxygen concentration and carbon dioxide concentration of the inhaled and exhaled gases for a predetermined period and using the average flow rate, oxygen concentration and carbon dioxide concentration to calculate an average volume of oxygen (VO₂) and average volume of carbon dioxide (VCO₂);

comparing average VO₂ for a predetermined number of consecutive time periods to determine if each of the average VO₂s are within a certain predetermined steady state range relative to each other; and

determining at least one respiratory parameter after VO₂ has attained a steady state.

58. The method as set forth in claim 57, further including the step of estimating a steady state VO₂ if the subject'"'"'s breathing does not reach a steady state.

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

60. The method as set forth in claim 54, wherein said step of calculating a respiratory parameter includes the step of calculating a resting metabolic rate using the volume of oxygen consumed (VO₂) by the subject and the volume of carbon dioxide produced (VCO₂).

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

62. The method as set forth in claim 54, wherein said oxygen sensor and said carbon dioxide sensor is a combined fluorescent quench sensor for measuring the concentration of carbon dioxide and the concentration of oxygen in the flow of inhaled and exhaled gases.

63. The method as set forth in claim 54, wherein said step of calculating at least one respiratory parameter further includes the step of determining a respiratory quotient using VO₂ and VCO₂.

64. The method as set forth in claim 54, wherein said flow meter includes an upper ultrasonic transducer and a lower ultrasonic transducer, each in fluid communication with the inhaled and exhaled gases passing through said flow pathway.

65. The calorimeter according to claim 64, wherein said ultrasonic transducer includes a plurality of microscopic transducers arranged in an array.

66. The method as set forth in claim 65, wherein said microscopic transducers measure temperature, pressure and humidity for correcting the gas flow rate due to the corresponding effects of temperature, pressure and humidity.