Determination of patency of the airway

• US 6,675,797 B1
• Filed: 01/18/2000
• Issued: 01/13/2004
• Est. Priority Date: 11/05/1993
• Status: Expired due to Fees

• Current Assignee: Resmed Limited (ResMed Incorporated)
• Original Assignee: Resmed Limited (ResMed Incorporated)
• Inventors: Berthon-Jones, Michael
• Primary Examiner(s): Lo, Weilun
• Assistant Examiner(s): WEISS JR, JOSEPH
• Application Number:
  US09/484,761
• Time in Patent Office: 1,456 Days
• Field of Search: 128/204.18, 128/204.21, 128/204.23, 128/204.24, 128/205.13, 128/205.18, 128/205.24, 128/205.25, 600/529, 600/533, 607/42
• US Class Current: 128/204.23
• CPC Class Codes: A61B 5/087 Measuring breath flow
• CPC Class Codes: A61B 5/7257 using Fourier transforms
• CPC Class Codes: A61F 5/56 Devices for preventing snoring by influencing the respiratory system by gas treatment A61M16/00
• CPC Class Codes: A61M 16/0006 with means for creating vibrations in patients' airways
• CPC Class Codes: A61M 16/0066 Blowers or centrifugal pumps
• 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 16/0875 Connecting tubes
• CPC Class Codes: A61M 2016/0039 in the inspiratory circuit
• CPC Class Codes: A61M 2230/60 Muscle strain, i.e. measured on the user

Abstract

Methods and apparatus for determining the occurrence of an apnea, patency and/or partial obstruction of the airway are disclosed. Respiratory air flow from a patient is measured to give an air flow signal. The determination of an apnea is performed by calculating the variance of the air flow signal over a moving time window and comparing the variance with a threshold value. One determination of partial obstruction of the airway is performed by detecting the inspiratory part of the air flow signal, scaling it to unity duration and area and calculating an index value of the amplitude of the scaled signal over a mid-portion. Alternatively, the index value is a measure of the flatness of the air flow signal over the mid-portion. One determination of patency of the airway is performed by applying an oscillatory pressure waveform of known frequency to a patient'"'"'s airway, calculating the magnitude of the component of said air flow signal at the known frequency induced by the oscillatory pressure waveform and comparing the calculated magnitude with a threshold value. Alternatively, the air flow signal is analysed to detect the presence of a component due to cardiogenic activity.

Claims

1. A method for determining patency of the airway of a patient to distinguish central from obstructive apnea events, the method comprising the steps of:

delivering an approximately constant level of pressure support above atmospheric to the patient during at least one respiratory cycle of the patient, the respiratory cycle having an inspiratory portion and an expiratory portion;

measuring respiratory air flow from the patient;

determining an occurrence of apnea from said respiratory air flow during delivery of the constant level of pressure support; and

if an apnea is determined then determining patency by

(a) applying an oscillatory pressure waveform of known frequency to the patient'"'"'s airway; and

(b) determining if the airway is patent from a component of said air flow at said known frequency induced by said oscillatory pressure waveform,

wherein a central obstructive apnea event is distinguished.

2. The method of claim 1 wherein said component is determined by demodulating said respiratory air flow.

3. The method of claim 1 wherein said component is an amplitude of said air flow signal, and said step of determining if the airway is patent involves a comparison of said component with a threshold value.

4. The method of claim 3 wherein the airway is determined to be patent if an amplitude of said component exceeds said threshold value.

5. The method of claim 3 wherein said component is derived as a mean of at least two components.

6. The method of claim 1 further comprising the step of delivering airway treatment pressure to said patient in response to the determination of patency.

7. The method of claim 6 wherein said step of delivering airway treatment pressure involves an increase in said pressure if said airway is determined not to be patent.

8. The method of claim 7 wherein said step of delivering airway treatment pressure involves no change or a reduction in said pressure if said airway is determined to be patent.

9. Apparatus for determining patency of the airway of a patient to distinguish central from obstructive apnea events, the apparatus comprising:

means for applying an oscillatory pressure waveform of known frequency to the patent'"'"'s airway and delivering an approximately constant level pressure support above atmospheric to the patient during at least one respiratory cycle of the patient, the respiratory cycle having an inspiratory portion and an expiratory portion;

means for measuring respiratory air flow from the patient; and

means for first determining an occurrence of apnea from said respiratory airflow during delivery of the constant level of pressure support, and if an apnea is occurring then subsequently applying said oscillatory pressure waveform and determining if the airway is patent by analysis of a component of said air flow at said known frequency induced by said oscillatory pressure waveform,

wherein a central or obstructive apnea event is distinguished.

10. The apparatus of claim 9 wherein said component is an amplitude of said air flow signal, and said analysis involves a comparison of said component with a threshold value.

11. The apparatus of claim 10 wherein patency is determined if an amplitude of said component exceeds said threshold value.

12. The apparatus of claim 10 wherein said component is derived as a mean of at least two components.

13. The apparatus of claim 9 wherein said means for applying comprises a means for delivering airway treatment pressure to said patient in response to said analysis.

14. The apparatus of claim 13 wherein said means for delivering airway treatment pressure increases said pressure if the airway is determined not to be patent.

15. The apparatus of claim 14 wherein said means for delivering airway treatment pressure involves no change or a reduction in said pressure if the airway is determined to be patent.

16. Apparatus for determining patency of the airway of a patient to distinguish central from obstructive apnea events, the apparatus comprising:

a turbine for applying an oscillatory pressure waveform of known frequency to the patient'"'"'s airway and delivering an approximately constant level of pressure support above atmospheric to the patient during at least one respiratory cycle of the patient, the respiratory cycle having an inspiratory portion and an expiratory portion;

a pressure transducer for generating a air flow signal representative of respiratory air flow from the patient; and

a processor with instructions for determining patency by (a) determining if an apnea is occurring during delivery of the approximately constant level of pressure support and (b) if an apnea is determined then initiating said oscillatory pressure waveform and determining if the airway is patent by an analysis of a component derived from said air flow signal at said known frequency induced by said oscillatory pressure waveform,

wherein a central or obstructive apnea event is distinguished.

17. The apparatus of claim 16 wherein said analysis involves a comparison of said component with a threshold value.

18. The apparatus of claim 17 wherein patency is determined if an amplitude of said component exceeds said threshold value.

19. The apparatus of claim 17 wherein said component is derived as a mean of at least two components.

20. The apparatus of claim 17 wherein said turbine comprises a means for delivering airway treatment pressure to said patient in response to said analysis.

21. The apparatus of claim 20 wherein said means for delivering airway treatment pressure increases said pressure if the airway is determined not to be patent.

22. The apparatus of claim 21 wherein said means for delivering airway treatment pressure involves no change or a reduction in said pressure if the airway is determined to be patent.

23. A method for determining a degree of patency of the airway of a patient to distinguish central from obstructive apnea events, the method comprising the steps of:

delivering an approximately constant level of pressure support above atmospheric to the patient during at least one respiratory cycle of the patient, the respiratory cycle having an inspiratory portion and an expiratory portion;

measuring respiratory air flow from the patient;

determining if an apnea is occurring from said respiratory air flow during delivery of the approximately constant level of pressure support; and

if an apnea is determined then

(a) applying an oscillatory pressure waveform of known frequency and a first magnitude to a patient'"'"'s airway;

(b) determining a second magnitude of a component of said air flow at said known frequency induced by said oscillatory pressure waveform; and

(c) determining a degree of patency as a function of said second magnitude,

wherein a central or obstructive apnea event is distinguished.

24. The method of claim 23 wherein said component is determined by demodulating said respiratory air flow.

25. The method of claim 23 where said function is a ratio of said first and second magnitudes.

26. The method of claim 25 further comprising the step of supplying airway treatment pressure to the patient'"'"'s airway based upon an assessment of said degree of patency.

27. The method of claim 26 wherein said airway treatment pressure is increased if said assessment of said degree of patency indicates that the patient'"'"'s airway is not open.

28. The method of claim 27 wherein said airway treatment pressure is decreased or unchanged if said assessment of said degree of patency indicates that the patient'"'"'s airway is open.

29. Apparatus for determining patency of the airway of a patient to distinguish central from obstructive apnea events, the apparatus comprising:

means for applying an oscillatory pressure waveform of known frequency and first magnitude to the patient'"'"'s airway and delivering an approximately constant level of pressure support above atmospheric to the patient during at least one respiratory cycle of the patient, the respiratory cycle having an inspiratory portion and an expiratory portion;

means for measuring respiratory air flow from the patient; and

means for determining an occurrence of apnea from said respiratory air flow during the delivery of the approximately constant level pressure support and if an apnea is occurring then (a) applying said oscillatory pressure waveform, (b) determining a second magnitude of a component of said air flow at said known frequency induced by said oscillatory pressure waveform, and (c) determining a degree of patency as a function of said second magnitude,

wherein a central or obstructive apnea event is distinguished.

30. The apparatus of claim 29 where said function is a ratio of said first and second magnitude.

31. The apparatus of claim 30 wherein said means for applying comprises a means for supplying airway treatment pressure to the patient'"'"'s airway based upon an assessment of said degree of patency.

32. The apparatus of claim 31 wherein said airway treatment pressure is increased if said assessment of said degree of patency indicates that the patient'"'"'s airway is not open.

33. The apparatus of claim 32 wherein said airway treatment pressure is decreased or unchanged if said assessment of said degree of patency indicates that the patient'"'"'s airway is open.

34. Apparatus for determining potency of the airway of a patient to distinguish central from obstructive apnea events, the apparatus comprising:

a turbine for applying an oscillatory pressure waveform of known frequency and a first magnitude to the patient'"'"'s airway and delivering an approximately constant level of pressure support above atmospheric to the patient during at least one respiratory cycle of the patient, the respiratory cycle having an inspiratory portion and an expiratory portion;

a pressure transducer for generating a air flow signal representative of respiratory air flow from the patient; and

a processor with instructions for determining patency by (a) determining if an apnea is occurring during delivery of the approximately constant level of pressure support and (b) if an apnea is determined then (1) applying said oscillatory pressure waveform, (2) determining a second magnitude of a component of said air flow at said known frequency induced by said oscillatory pressure waveform, and (3) determining a degree of patency as a function of said second magnitudes,

wherein a central or obstructive apnea event is distinguished.

35. The apparatus of claim 34 where said function is a ratio of said first and second magnitude.

36. The apparatus of claim 35 wherein said instruction further cause said turbine to supply airway treatment pressure to the patient'"'"'s airway based upon an assessment of said degree of patency.

37. The apparatus of claim 36 wherein said airway treatment pressure is increased if said assessment of said degree of patency indicates that the patient'"'"'s airway is not open.

38. The apparatus of claim 37 wherein said airway treatment pressure is decreased or unchanged if said assessment of said degree of patency indicates that the patient'"'"'s airway is open.

39. A method for determining patency of the airway of the patient to distinguish central from obstructive apnea events, during administration of continuous positive airway pressure to treat a patient having sleep apnea the method, comprising the steps of:

measuring respiratory airflow from the patient;

determining an occurrence of apnea from the respiratory airflow during delivery of the continuous positive airway pressure; and

if an apnea is determined then determining patency by

(a) applying a small test pressure oscillation of a known frequency and of a non-treatment amplitude for a period of time to the airway of the patient; and

(b) determining if the airway is patent from a component of the airflow at the frequency induced by the pressure oscillation,

wherein a central or obstructive apnea event is distinguished.

40. The method of claim 39 wherein the known frequency is a low frequency of about 2 Hz.

41. The method of claim 39 wherein the non-treatment amplitude is less than 3 cm H₂O.

42. The method of claim 41 wherein the non-treatment amplitude is approximately 1 cm H₂O.

43. The method of claim 39 wherein the period of time is approximately 6 seconds.

44. The method of claim 42 wherein the small test pressure oscillation is applied upon a level of positive airway pressure sufficient to splint the airway of the patient.