Methods and apparatus for determining instantaneous elastic recoil and assistance pressure during ventilatory support

• US 6,688,307 B2
• Filed: 03/12/2002
• Issued: 02/10/2004
• Est. Priority Date: 09/23/1996
• Status: Expired due to Term

• Current Assignee: Resmed Limited (ResMed Incorporated)
• Original Assignee: Resmed Limited (ResMed Incorporated)
• Inventors: Berthon-Jones, Michael
• Primary Examiner(s): Lewis, Aaron J.
• Application Number:
  US10/095,904
• Publication Number:
  US 20020148466A1
• Time in Patent Office: 700 Days
• Field of Search: 128/200.24, 128/204.21, 128/204.23, 128/204.18, 600/533, 600/538, 700/50, 706/7-9
• US Class Current: 128/204.21
• CPC Class Codes: A61B 5/085 Measuring impedance of respiratory organs or lung elasticity
• CPC Class Codes: A61B 5/087 Measuring breath flow
• CPC Class Codes: A61B 5/7264 Classification of physiological signals or data, e.g. using neural networks, statistical classifiers, expert systems or fuzzy systems neural networks per se G06N3/00; expert systems per se G06N5/00
• CPC Class Codes: A61M 16/00 Devices for influencing the respiratory system of patients by gas treatment, e.g. mouth-to-mouth respiration; Tracheal tubes stimulating the respiratory movement by mechanical, pneumatic or electrical means, iron lungs combined with gas breathing means A61H31/00
• CPC Class Codes: A61M 16/0003 Accessories therefor, e.g. sensors, vibrators, negative pressure
• CPC Class Codes: A61M 16/0069 the speed thereof being controlled by respiratory parameters, e.g. by inhalation
• CPC Class Codes: A61M 16/024 including calculation means, e.g. using a processor
• CPC Class Codes: A61M 16/06 Respiratory or anaesthetic masks
• CPC Class Codes: A61M 16/1055 bacterial
• CPC Class Codes: A61M 16/107 in the inspiratory path
• CPC Class Codes: A61M 2016/0021 with a proportional output signal, e.g. from a thermistor
• 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 2205/15 Detection of leaks
• CPC Class Codes: G16H 50/20 for computer-aided diagnosis, e.g. based on medical expert systems

Abstract

The apparatus provides for the determination of the instantaneous phase in the respiratory cycle, subject'"'"'s average respiration rate and the provision of ventilatory assistance. A microprocessor (16) receives an airflow signal from a pressure transducer (18) coupled to a port (17) at a mask (11). The microprocessor (16) controls a servo (19), that in turn controls the fan motor (20) and thus the pressure of air delivered by the blower (10). The blower (10) is coupled to a subject'"'"'s mask (ii) by a conduit (12). The invention seeks to address the following goals: while the subject is awake and making substantial efforts the delivered assistance should be closely matched in phase with the subject'"'"'s efforts; the machine should automatically adjust the degree of assistance to maintain at least a specified minimum ventilation without relying on the integrity of the subject'"'"'s chemoreflexes; and it should continue to work correctly in the pesence of large leaks.

Claims

1. A method for determining an instantaneous elastic recoil pressure comprising the steps of:

specifying an elastance for a subject;

providing the subject with ventilatory support;

determining a measure of respiratory airflow;

determining an index value representing an extent to which a leak is suddenly changing using said measure of respiratory airflow;

calculating an inspired volume of airflow as a function of said measure of respiratory airflow and said index value and;

calculating said instantaneous elastic recoil pressure as a function of said inspired volume and said elastance.

2. The method of claim 1 wherein said elastance is about 50 to 75 percent of the subject'"'"'s lung and chest wall elasticity.

3. The method of claim 2 wherein said index value is a fuzzy logic function of the fuzzy extent to which a leak has suddenly increased and the fuzzy extent to which a leak has suddenly decreased.

4. The method of claim 3 wherein (a) said fuzzy logic function is the fuzzy negation of a peak fuzzy union of said fuzzy extent to which a leak has suddenly increased and said fuzzy extent to which a leak has suddenly decreased;

and (b) said function of said measure of respiratory airflow and said index value is an integral of a product of said measure and a function of said index value.

5. An apparatus for determining an instantaneous elastic recoil pressure during the provision of respiratory assistance comprising:

an air supply means controllable to supply breathable air to a subject'"'"'s airway continually at a selectable pressure elevated above atmospheric pressure as a function of an instantaneous elastic pressure;

a flow sensor means to generate a flow signal representative of respiratory airflow; and

a processor means to process a flow signal from said flow sensor and to control said air supply means, wherein said processor is programmed to;

receive as input an elastance value for a subject;

calculate an index value representing an extent to which any leak is suddenly changing using sampled flow values from said flow signal;

calculating an inspired volume of airflow as a function of said measure of respiratory airflow and said index value; and

calculating said instantaneous elastic recoil pressure as a function of said inspired volume and said elastance value.

6. The apparatus of claim 5 wherein said index value is calculated from a fuzzy logic function of the fuzzy extent to which said flow samples indicate that a leak has suddenly increased and the fuzzy extent to which said flow samples indicate a leak has suddenly decreased.

7. The apparatus of claim 6 wherein (a) said fuzzy logic function is the fuzzy negation of a peak fuzzy union of said fuzzy extent to which a leak has suddenly increased and said fuzzy extent to which a leak has suddenly decreased;

and (b) said function of said measure of respiratory airflow and said index value is an integral of a product of said measure and a function of said index value.

8. An apparatus for determining an instantaneous elastic recoil pressure during the provision of respiratory assistance comprising:

a blower and mask to supply breathable air to a subject'"'"'s airway continually at a selectable pressure elevated above atmospheric pressure as a function of an instantaneous elastic pressure;

a pressure transducer to generate a flow signal representative of respiratory airflow; and

a processor to process a flow signal from said pressure transducer and to control said blower, wherein said processor is programmed to;

receive as input an elastance value for a subject;

calculate an index value representing an extent to which any leak is suddenly changing using sampled flow values from said flow signal;

calculating an inspired volume of airflow as a function of said measure of respiratory airflow and said index value; and

calculating said instantaneous elastic recoil pressure as a function of said inspired volume and said elastance value.

9. The apparatus of claim 8 wherein said index value is calculated from a fuzzy logic function of the fuzzy extent to which said flow samples indicate that a leak has suddenly increased and the fuzzy extent to which said flow samples indicate a leak has suddenly decreased.

10. The apparatus of claim 9 wherein (a) said fuzzy logic function is the fuzzy negation of a peak fuzzy union of said fuzzy extent to which a leak has suddenly increased and said fuzzy extent to which a leak has suddenly decreased;

and (b) said function of said measure of respiratory airflow and said index value is an integral of a product of said measure and a function of said index value.

11. A method for determining an instantaneous elastic recoil pressure comprising the steps of:

specifying an elastance for a subject;

specifying a ventilation target;

providing the subject with respiratory support;

calculating a phase index representing a phase in the subject'"'"'s respiration;

calculating said instantaneous elastic recoil pressure as a function of (a) said elastance, (b) said ventilation target, and (c) a function of said phase index.

12. The method of claim 11 wherein said ventilation target is a tidal volume.

13. The method of claim 12 wherein said elastance is about 50 to 75 percent of the subject'"'"'s lung and chest wall elasticity.

14. The method of claim 13 wherein said function of said phase index is a waveform template.

15. An apparatus for determining an instantaneous elastic recoil pressure during the provision of respiratory assistance comprising:

an air supply means controllable to supply breathable air to a subject'"'"'s airway continually at a selectable pressure elevated above atmospheric pressure as a function of an instantaneous elastic recoil pressure;

a flow sensor means to generate a flow signal representative of respiratory airflow; and

a processor means to process a flow signal from said flow sensor and to control said air supply means, wherein said processor is programmed to;

accept an elastance value for a subject;

accept a ventilation target;

calculate a phase index representing the instantaneous phase in the subject'"'"'s respiration;

calculate said instantaneous elastic recoil pressure as a function of (a) said elastance, (b) said ventilation target, and (c) a function of said phase index.

16. The apparatus of claim 15 wherein said ventilation target is a tidal volume.

17. The apparatus of claim 16 wherein said function of said phase index is a waveform template.

18. An apparatus for determining an instantaneous elastic recoil pressure during the provision of respiratory assistance comprising:

a blower and mask to supply breathable air to a subject'"'"'s airway continually at a selectable pressure elevated above atmospheric pressure as a function of an instantaneous elastic recoil pressure;

a pressure transducer to generate a flow signal representative of respiratory airflow; and

a processor to process a flow signal from said pressure transducer and to control said blower, wherein said processor is programmed to;

accept an elastance value for a subject;

accept a ventilation target;

calculate a phase index representing the instantaneous phase in the subject'"'"'s respiration;

calculate said instantaneous elastic recoil pressure as a function of (a) said elastance, (b) said ventilation target, and (c) a function of said phase index.

19. The apparatus of claim 18 wherein said ventilation target is a tidal volume.

20. The apparatus of claim 19 wherein said function of said phase index is a waveform template.

21. A method for determining an instantaneous elastic recoil pressure comprising the steps of:

specifying an elastance for a subject;

specifying a ventilation target;

providing the subject with respiratory support;

calculating a phase index representing a phase in the subject'"'"'s respiration from said flow signal;

calculating the subject'"'"'s respiratory rate; and

calculating said instantaneous elastic recoil pressure as a function of (a) the elastance, (b) the ventilation target, (c) the respiratory rate, and (d) a function of the phase index.

22. The method of claim 21 wherein said ventilation target is a tidal volume.

23. The method of claim 22 wherein said elastance is about 50 to 75 percent of the subject'"'"'s lung and chest wall elasticity.

24. The method of claim 23 wherein said function of said phase index is a waveform template.

25. An apparatus for determining an instantaneous elastic recoil pressure during the provision of respiratory assistance comprising:

an air supply means controllable to supply breathable air to a subject'"'"'s airway continually at a selectable pressure elevated above atmospheric pressure as a function of an instantaneous elastic recoil pressure;

a flow sensor means to generate a flow signal representative of respiratory airflow; and

a processor means to process a flow signal from said flow sensor and to control said air supply means, wherein said processor is programmed to;

accept an elastance value for a subject;

accept a ventilation target;

calculate a phase index representing a phase in the subject'"'"'s respiration using flow values sampled from said flow signal;

calculate the subject'"'"'s respiratory rate; and

calculate said instantaneous elastic recoil pressure as a function of (a) the elastance, (b) the ventilation target, (c) the respiratory rate, and (d) a function of the phase index.

26. The apparatus of claim 25 wherein said ventilation target is a tidal volume.

27. The apparatus of claim 26 wherein said function of said phase index is a waveform template.

28. An apparatus for determining an instantaneous elastic recoil pressure during the provision of respiratory assistance comprising:

a blower and mask to supply breathable air to a subject'"'"'s airway continually at a selectable pressure elevated above atmospheric pressure as a function of an instantaneous elastic recoil pressure;

a pressure transducer to generate a flow signal representative of respiratory airflow; and

a processor to process a flow signal from said pressure transducer and to control said blower, wherein said processor is programmed to;

accept an elastance value for a subject;

accept a ventilation target;

calculate a phase index representing a phase in the subject'"'"'s respiration using flow values sampled from said flow signal;

calculate the subject'"'"'s respiratory rate; and

calculate said instantaneous elastic recoil pressure as a function of (a) the elastance, (b) the ventilation target, (c) the respiratory rate, and (d) a function of the phase index.

29. The apparatus of claim 28 wherein said ventilation target is a tidal volume.

30. The apparatus of claim 29 wherein said function of said phase index is a waveform template.

31. A method for determining an instantaneous elastic recoil pressure comprising the steps of:

providing the subject with respiratory support;

calculating a phase index representing an instantaneous phase in the subject'"'"'s respiration;

determining instantaneous elastic assistance pressure;

low pass filtering said instantaneous elastic assistance pressure; and

calculating said instantaneous elastic recoil pressure from a function of the low pass filtered instantaneous elastic assistance pressure and a function of the phase index.

32. The method of claim 31 wherein said function of the phase index is a ratio of the phase index as applied to a pressure waveform template function and its mean.

33. An apparatus for determining an instantaneous elastic recoil pressure during the provision of respiratory assistance comprising:

an air supply means controllable to supply breathable air to a subject'"'"'s airway continually at a selectable pressure elevated above atmospheric pressure as a function of an instantaneous elastic pressure;

a flow sensor means to generate a flow signal representative of respiratory airflow; and

a processor means to process a flow signal from said flow sensor and to control said air supply means, wherein said processor is programmed to;

calculate a phase index representing a phase in the subject'"'"'s respiration using flow values sampled from said flow signal;

calculate an instantaneous elastic assistance pressure;

low pass filter said instantaneous elastic assistance pressure; and

calculate said instantaneous elastic recoil pressure from a function of the low pass filtered instantaneous elastic assistance pressure and a function of the phase index.

34. The apparatus of claim 33 wherein said function of the phase index is a ratio of the phase index as applied to a pressure wave template function and its mean.

35. An apparatus for determining an instantaneous elastic recoil pressure during the provision of respiratory assistance comprising:

a blower and mask controllable to supply breathable air to a subject'"'"'s airway continually at a selectable pressure elevated above atmospheric pressure as a function of an instantaneous elastic pressure;

a pressure transducer to generate a flow signal representative of respiratory airflow; and

a processor to process a flow signal from said pressure transducer and to control said blower, wherein said processor is programmed to;

calculate a phase index representing a phase in the subject'"'"'s respiration using flow values sampled from said flow signal;

calculate an instantaneous elastic assistance pressure;

low pass filter said instantaneous elastic assistance pressure; and

calculate said instantaneous elastic recoil pressure from a function of the low pass filtered instantaneous elastic assistance pressure and a function of the phase index.

36. The apparatus of claim 35 wherein said function of the phase index is a ratio of the phase index as applied to a pressure wave template function and its mean.

37. A method for determining an instantaneous elastic assistance pressure during the provision of respiratory support comprising the steps of:

specifying an elastance for a subject;

providing the subject with ventilatory support;

calculating two or more estimated values for instantaneous elastic recoil pressure as a function of said elastance;

calculating a weighted average recoil pressure from a weighted average of said estimated values; and

determining an instantaneous elastic assistance pressure as a function of the weighted average recoil pressure.

38. The method of claim 37 wherein said weighted average is a function of a selected pressure waveform.

39. The method of claim 38 wherein said instantaneous elastic assistance pressure is a further function of a specified minimum pressure swing and a calculated instantaneous phase determined from a measure of respiration.

40. The method of claim 39 wherein said instantaneous elastic assistance pressure is a further function of a pressure amplitude for maintaining at least an average target ventilation.

41. The method of claim 40 wherein said average target ventilation is a minute ventilation.

42. The method of claim 41 wherein said elastance is about 29 to 54 percent of the subject'"'"'s lung and chest wall elasticity.

43. The method of claim 37 wherein one of said estimated values of elastic recoil pressure is derived by:

determining a measure of respiratory airflow;

determining an index value representing an extent to which any leak is suddenly changing using said measure of respiratory airflow;

calculating an inspired volume of airflow as an integral of a function of said index value and said measure of respiratory airflow; and

calculating an estimated value of elastic recoil pressure as a function of said inspired volume and said elastance.

44. The method of claim 43 wherein one of said estimated values of elastic recoil pressure is derived by the steps of:

determining a target tidal volume;

calculating a phase index representing a phase in the subject'"'"'s respiration; and

calculating an estimated value of elastic recoil pressure as a function of (a) said elastance, (b) said target tidal volume, and (c) a function of the phase index.

45. The method of claim 44 wherein one of said estimated values of elastic recoil pressure is derived by the steps of:

specifying a target ventilation;

calculating the subject'"'"'s respiratory rate; and

calculating an estimated value of elastic recoil pressure from a function of (a) the elastance, (b) the target ventilation, (c) the respiratory rate, and (d) a function of the phase index.

46. The method of claim 45 wherein one of said estimated values of elastic recoil pressure is derived by the steps of:

low pass filtering a previously determined instantaneous elastic assistance; and

calculating an estimated value of elastic recoil pressure from a function of the low pass filtered instantaneous elastic assistance and a function of the phase index.

47. An apparatus for determining an instantaneous elastic assistance pressure during the provision of respiratory assistance comprising:

an air supply means controllable to supply breathable air to a patient'"'"'s airway continually at a selectable pressure elevated above atmospheric pressure as a function of an instantaneous elastic assistance pressure value;

a flow sensor means to generate a flow signal representative of respiratory airflow; and

a processor means to process a flow signal from said flow sensor and to control said air supply means, wherein said processor is programmed to;

receive as input an elastance value for a patient;

calculate two or more estimated elastic recoil pressure values as a function of said elastance value;

calculate a weighted average recoil pressure value from a weighted average of said estimated values; and

determine the instantaneous elastic assistance pressure value as a function of the weighted average recoil pressure value.

48. The apparatus of claim 47 wherein said weighted average is a function of a selected pressure waveform.

49. The apparatus of claim 48 wherein said instantaneous elastic assistance pressure is a further function of a specified minimum pressure swing and a calculated instantaneous phase value determined using flow values sampled from said flow signal.

50. The apparatus of claim 49 wherein said instantaneous elastic assistance pressure is a further function of a pressure amplitude for maintaining at least an average target ventilation.

51. The apparatus of claim 50 wherein said average target ventilation is a minute ventilation.

52. The apparatus of claim 47 wherein one of said estimated values of elastic recoil pressure is calculated by said processor through the steps of:

determining an index value representing an extent to which any leak is suddenly changing using flow values sampled from said flow signal;

calculating an inspired volume of airflow as an integral of a function of said index value and said flow values; and

calculating an estimated value of elastic recoil pressure as a function of said inspired volume and said elastance value.

53. The apparatus of claim 52 wherein one of said estimated values of elastic recoil pressure is calculated by said processor through the steps of:

processing a target tidal volume value;

calculating a phase index representing a phase in the subject'"'"'s respiration using said flow values; and

calculating an estimated value of elastic recoil pressure as a function of (a) said elastance value, (b) said target tidal volume value, and (c) a function of the phase index.

54. The apparatus of claim 53 wherein one of said estimated values of elastic recoil pressure is calculated by said processor through the steps of:

processing a target ventilation value;

calculating the subject'"'"'s respiratory rate; and

calculating an estimated value of elastic recoil pressure from a function of (a) the elastance value, (b) the target ventilation value, (c) the respiratory rate, and (d) a function of the phase index.

55. The apparatus of claim 54 wherein one of said estimated values of elastic recoil pressure is calculated by said processor through the steps of:

low pass filtering a previously determined instantaneous elastic assistance pressure value; and

calculating an estimated value of elastic recoil pressure from a function of the low pass filtered instantaneous elastic assistance value and a function of the phase index.

56. An apparatus for determining an instantaneous elastic assistance pressure during the provision of respiratory assistance comprising:

a blower and mask controllable to supply breathable air to a patient'"'"'s airway continually at a selectable pressure elevated above atmospheric pressure as a function of an instantaneous elastic assistance pressure value;

a pressure transducer to generate a flow signal representative of respiratory airflow; and

a processor to process a flow signal from said pressure transducer and to control said blower, wherein said processor is programmed to;

receive as input an elastance value for a patient;

calculate two or more estimated elastic recoil pressure values as a function of said elastance value;

calculate a weighted average recoil pressure value from a weighted average of said estimated values; and

determine the instantaneous elastic assistance pressure value as a function of the weighted average recoil pressure value.

57. The apparatus of claim 56 wherein said weighted average is a function of a selected pressure waveform.

58. The apparatus of claim 57 wherein said instantaneous elastic assistance pressure is a further function of a specified minimum pressure swing and a calculated instantaneous phase value determined using flow values sampled from said flow signal.

59. The apparatus of claim 58 wherein said instantaneous elastic assistance pressure is a further function of a pressure amplitude for maintaining at least an average target ventilation.

60. The apparatus of claim 59 wherein said average target ventilation is a minute ventilation.

61. The apparatus of claim 56 wherein one of said estimated values of elastic recoil pressure is calculated by said processor through the steps of:

determining an index value representing an extent to which any leak is suddenly changing using flow values sampled from said flow signal;

calculating an inspired volume of airflow as an integral of a function of said index value and said flow values; and

calculating an estimated value of elastic recoil pressure as a function of said inspired volume and said elastance value.

62. The apparatus of claim 61 wherein one of said estimated values of elastic recoil pressure is calculated by said processor through the steps of:

processing a target tidal volume value;

calculating a phase index representing a phase in the subject'"'"'s respiration using said flow values; and

calculating an estimated value of elastic recoil pressure as a function of (a) said elastance value, (b) said target tidal volume value, and (c) a function of the phase index.

63. The apparatus of claim 62 wherein one of said estimated values of elastic recoil pressure is calculated by said processor through the steps of:

processing a target ventilation value;

calculating the subject'"'"'s respiratory rate; and

calculating an estimated value of elastic recoil pressure from a function of (a) the elastance value, (b) the target ventilation value, (c) the respiratory rate, and (d) a function of the phase index.

64. The apparatus of claim 63 wherein one of said estimated values of elastic recoil pressure is calculated by said processor through the steps of:

low pass filtering a previously determined instantaneous elastic assistance pressure value; and

calculating an estimated value of elastic recoil pressure from a function of the low pass filtered instantaneous elastic assistance value and a function of the phase index.