Determination of Apnea type

• US 6,375,623 B1
• Filed: 10/06/2000
• Issued: 04/23/2002
• Est. Priority Date: 04/08/1998
• Status: Expired due to Term

• Current Assignee: Isonea Limited
• Original Assignee: Karmel Medical Acoustic Technologies Ltd. (Noam Gavriely, MD)
• Inventors: Gavriely, Noam
• Primary Examiner(s): Shaver, Kevin
• Assistant Examiner(s): Natnithithadha, Navin
• Application Number:
  US09/647,947
• Time in Patent Office: 564 Days
• Field of Search: 600/534, 600/535, 600/529, 600/595, 600/586
• US Class Current: 600/534
• CPC Class Codes: A61B 5/1135 by monitoring thoracic expansion
• 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: G16H 50/20 for computer-aided diagnosis, e.g. based on medical expert systems

Abstract

A method of differentiating between OSA and CSA comprising: determining if chest motion above a chest motion threshold is present; determining if tracheal breath sound above a breath sounds threshold are present, classifying a state as OSA if the chest motion is above the threshold and the sounds are below the threshold; and classifying a state as CSA if both the chest motion and sounds are below their respective thresholds.

Claims

1. A method of differentiating between OSA and CSA comprising:

determining if chest motion above a chest motion threshold is present;

determining if tracheal breath sound above a breath sounds threshold are present;

classifying a state as OSA if the chest motion is above the threshold and the sounds are below the threshold; and

classifying a state as CSA if both the chest motion and sounds are below their respective thresholds.

2. A method according to claim 1 wherein said determining is performed on time segments of the chest motion and breath sounds.

3. A method according to claim 1 wherein the chest motion threshold is determined based on a percentage of motion during normal breathing.

4. A method according to claim 3 wherein the chest motion threshold is between about 5% and about 10%.

5. A method according to claim 3 wherein the chest motion threshold is about 10% of a normal breathing chest motion.

6. A method according to claim 3 wherein the normal breathing is normal breathing during sleep.

7. A method according to claim 1 wherein determining whether tracheal breath sounds are present includes:

producing a spectrum of the breath sound signal;

summing averaging the spectrum over a given frequency range to produce a breath sounds power signal.

8. A method according to claim 7 and including producing a separate breath sound spectrum for each of a plurality of given time periods.

9. A method according to claim 1 and including:

producing a breath sounds power signal representative of the breath sounds power in a plurality of given time periods; and

integration circuitry which receives the breath sounds power signal; and

producing a running time average or integral of the breath sounds power signal over a second given time period.

10. Breath sounds apparatus for classifying a breathing state comprising:

a chest motion sensor and produces a chest motion signal;

a tracheal breath sound sensor that produces a breath sound signal;

computing circuitry that receives the breath sound signal and the chest motion signal and determines if chest motion above a chest motion threshold is present and if tracheal breath sound above a breath sounds threshold is present and classifies a breathing state as OSA if the chest motion is above the threshold and the sounds are below the threshold and classifies a breathing state as CSA if both the chest motion and sounds are below their respective thresholds.

11. Breath sounds apparatus according to claim 10 wherein the computing circuitry includes:

spectrum producing circuitry which receives the breath sound signal and produces a spectrum of the breath sound signal; and

averaging circuitry which receives the spectrum and sums or averages the spectrum over a given frequency range to produce a breath sounds power signal, wherein the breath sounds power signal is used in the determination of whether the breath sounds are above their threshold.

12. Apparatus according to claim 11 wherein the given frequency range has a lower frequency limit of at least 200 Hz.

13. Apparatus according to claim 11 wherein the given frequency range has a lower frequency limit of at least 250 Hz.

14. Apparatus according to claim 11 wherein the given frequency range has a lower frequency limit of at least 300 Hz.

15. Apparatus according to claim 11 wherein the given frequency range has a lower frequency limit of at least 350 Hz.

16. Apparatus according to claim 11 wherein the given frequency range has a lower frequency limit of at least 400 Hz.

17. Apparatus according to claim 12 wherein the given frequency range has an upper frequency limit of 1200 Hz or less.

18. Apparatus according to claim 12 wherein the given frequency range has an upper frequency limit of 1300 Hz or less.

19. Apparatus according to claim 12 wherein the given frequency range has an upper frequency limit of 1400 Hz or less.

20. Apparatus according to claim 12 wherein the given frequency range has an upper frequency limit of 1500 Hz or less.

21. Apparatus according to claim 12 wherein the given frequency range has an upper frequency limit of 1800 Hz or less.

22. Apparatus according to claim 12 wherein the given frequency range has an upper frequency limit of 2000 Hz or less.

23. Apparatus according to claim 11 wherein the given frequency range is at least 800 Hz.

24. Apparatus according to claim 11, wherein the spectrum producing circuitry produces a separate breath sound spectrum for each of a plurality of given time periods.

25. Apparatus according to claim 24 wherein the given time period is greater than 20 msec.

26. Apparatus according to claim 24 wherein the given time period is greater than 50 msec.

27. Apparatus according to claim 24 wherein the given time period is greater than 75 msec.

28. Apparatus according to claim 24 wherein the given time period is shorter than 200 msec.

29. Apparatus according to claim 24 wherein the given time period is shorter than 150 msec.

30. Apparatus according to claim 24 wherein the given time period is shorter than 100 msec.

31. Apparatus according to claim 24 wherein the given time period is shorter than 75 msec.

32. Apparatus according to claim 24 wherein the given time period is shorter than 50 msec.

33. Apparatus according to claim 11 and including integration circuitry which receives the breath sounds power signal and produces a running time average or integral of the breath sounds power signal over a second given time period.

34. Apparatus according to claim 33 wherein the second given time period is at least 5 seconds.

35. Apparatus according to claim 33 wherein the second given time period is about 6 seconds.

36. Apparatus according to claim 33 wherein the second given time period is about 8 seconds.

37. Apparatus according to claim 33 wherein the second given time period is about 10 seconds.

38. Apparatus according to claim 33 wherein the second given time period is between about 10-15 seconds.

39. Apparatus according to claim 33 wherein the second given time period is between about 15-20 seconds.

40. Apparatus according to claim 11 and including comparison circuitry which receives the averaged or integrated breath sounds power signal and produces an apnea indication if the averaged breath sounds power signal is below a given apnea threshold.

41. Apparatus according to claim 40 wherein the given apnea threshold is based on a breath sounds power signal acquired during normal breathing.

42. Apparatus according to claim 41 wherein the given apnea threshold is about 10% of the a breath sounds power signal acquired during normal breathing.

43. Apparatus according to claim 42 wherein the given apnea threshold is between 5% and 10% of the a breath sounds power signal acquired during normal breathing.

44. Apparatus according to claim 11 and including comparison circuitry which receives the averaged or integrated breath sounds power signal and produces an hypopnea indication if the averaged breath sounds power signal is below a given hypopnea threshold.

45. Apparatus according to claim 44 wherein the given hypopnea threshold is based on a breath sounds power signal acquired during normal breathing.

46. Apparatus according to claim 45 wherein the given hypopnea threshold is about 25% of the a breath sounds power signal acquired during normal breathing.

47. Apparatus according to claim 45 wherein the given apnea threshold is between 20% and 30% of the a breath sounds power signal acquired during normal breathing.

48. Apparatus according to claim 10 and including:

an ambient sound sensor which produces an ambient sound signal responsive to ambient sounds;

spectrum producing circuitry which receives the ambient sound signal and produces a spectrum of the ambient sound signal;

comparison circuitry which compares the spectrum of the ambient sound spectrum with a threshold spectrum and produces a signal for those frequencies for which the spectrum is greater than the threshold; and

spectrum conditioning circuitry which conditions the breath sound spectrum by replacing the value of the breaths sounds spectrum by a different value for those frequencies for which the ambient sound spectrum exceeds the threshold.

49. Apparatus according to claim 48 wherein the threshold is based on an ambient sounds spectrum produced in the absence of substantial ambient sound.

50. Apparatus according to claim 49 wherein the threshold at a given frequency is determined, from a plurality of spectra of the ambient sound, as the average of value of the spectrum at the given frequency plus a factor times the standard deviation of the values of the spectrum.

51. Apparatus according to claim 50 wherein the factor is more than 3.

52. Apparatus according to claim 51 wherein the factor is between 4 and 6.

53. Apparatus according to claim 48 wherein the spectrum conditioning circuit replaces the value of the breaths sounds spectrum by a zero for those frequencies for which the ambient sound spectrum exceeds the threshold.

54. Apparatus according to claim 48 wherein the spectrum conditioning circuit replaces the value of the breaths sounds spectrum by a value equal to the average of values for adjacent frequencies, for those frequencies for which the ambient sound spectrum exceeds the threshold.