Respiratory effort detection method and apparatus

• US 5,944,680 A
• Filed: 06/26/1996
• Issued: 08/31/1999
• Est. Priority Date: 06/26/1996
• Status: Expired due to Term

• Current Assignee: Medtronic Incorporated (Medtronic Plc)
• Original Assignee: Medtronic Incorporated (Medtronic Plc)
• Inventors: Hammargren, John, Neisz, Johann J., Christopherson, Mark A.
• Primary Examiner(s): Yu, Mickey
• Assistant Examiner(s): Nguyen, Dinh X.
• Application Number:
  US08/674,494
• Time in Patent Office: 1,161 Days
• Field of Search: 607/42, 607/46, 607/48, 122/716, 122/725, 128/897, 128/898, 128/716, 128/725, 600/529, 600/532, 600/533, 600/534, 600/538
• US Class Current: 602/42
• CPC Class Codes: A61B 5/03 Detecting, measuring or recording fluid pressure within the body other than blood pressure, e.g. cerebral pressure; Measuring pressure in body tissues or organs A61B5/205 takes precedence
• CPC Class Codes: A61B 5/07 Endoradiosondes
• CPC Class Codes: A61B 5/113 occurring during breathing
• CPC Class Codes: A61N 1/3601 of respiratory organs

Abstract

A method of predicting critical points in patient respiration includes monitoring at least one characteristic of a respiratory effort waveform of a patient to detect a respiratory event. A refractory period is defined that includes a hard refractory period during which time the respiratory event cannot be responded to and a soft refractory period following the hard refractory period. The respiratory event outside of the refractory period is detected as a function of a first set of predetermined parameters for the monitored at least one characteristic and the respiratory event within the soft refractory period is detected as a function of a second set of predetermined parameters for the monitored at least one characteristic. The respiratory event may be inspiration onset and the characteristic of the respiratory effort waveform monitored is at least one of slope and amplitude. The refractory period may be defined based on detection of inspiration offset and further may be defined based on inspiration offset, an average respiratory period, and an average time of inspiration. Further, stimulation may be provided in response to a detected inspiration onset. Another method of predicting critical points includes sampling the amplitude of the respiratory effort waveform of a patient. A sample signal is generated representative of at least one characteristic of the respiratory effort waveform based on each amplitude sample. The sample signals representative of the at least one characteristic of the respiratory effort waveform are monitored and a respiratory event is detected as a function of at least two sample signals. Apparatus and systems for use with such methods are also described.

Claims

1. A method of predicting critical points in patient respiration, the method comprising the steps of:

monitoring at least one characteristic of a respiratory effort waveform of a patient to detect a respiratory event;

defining a refractory period including a hard refractory period during which time the respiratory event cannot be responded to and a soft refractory period following the hard refractory period;

detecting the respiratory event outside of the refractory period as a function of a first set of predetermined parameters for the monitored at least one characteristic; and

detecting the respiratory event within the soft refractory period as a function of a second set of predetermined parameters for the monitored at least one characteristic.

2. The method according to claim 1, wherein the respiratory event is inspiration onset and further wherein the at least one characteristic of the respiratory effort waveform monitored is at least one of slope and amplitude.

3. The method according to claim 2, wherein the step of detecting inspiration onset outside of the refractory period includes the step of detecting inspiration onset outside of the refractory period as a function of monitored slope of the respiratory effort waveform, and further wherein the step of detecting inspiration onset within the soft refractory period includes the step of detecting inspiration onset within the soft refractory period as a function of monitored slope and amplitude of the respiratory effort waveform.

4. The method according to claim 1, wherein the refractory period is defined based on detection of inspiration offset.

5. The method according to claim 2, wherein the refractory period is defined based on detection of inspiration offset and further wherein the method includes the step of detecting inspiration offset as a function of the monitored slope and amplitude of the respiratory effort waveform.

6. The method according to claim 5, wherein the monitoring step includes sampling the amplitude of the respiratory effort waveform and generating slope values representative of the respiratory effort waveform based on the amplitude samples, and further wherein the detection of inspiration offset includes the steps of:

comparing the slope values to a predetermined slope value offset threshold in a first comparison step;

comparing the amplitude of the sampled respiratory effort waveform to a predetermined amplitude offset threshold in a second comparison step;

detecting inspiration offset as a function of the first comparison step and second comparison step.

7. The method according to claim 6, wherein the detection of inspiration offset further includes validating the detected inspiration offset by comparing the amplitude of the sampled respiratory waveform to a validating offset threshold.

8. The method according to claim 6, wherein the detecting inspiration offset step further includes the step of detecting inspiration offset if a predetermined number of slope values satisfies the slope value offset threshold and the amplitude of at least the first of the predetermined number of slope values satisfies the amplitude offset threshold.

9. The method according to claim 2, wherein the monitoring step includes sampling the amplitude of the respiratory effort waveform signal and generating slope values representative of the respiratory effort waveform based on the amplitude samples, and further wherein the detection of inspiration onset outside of the refractory period includes the step of detecting an inspiration onset as a function of a comparison of the slope values to a predetermined slope value onset threshold.

10. The method according to claim 9, wherein the detection of inspiration onset outside of the refractory period includes detecting inspiration onset if a predetermined number of slope values satisfy the predetermined slope value onset threshold.

11. The method according to claim 2, wherein the monitoring step includes sampling the amplitude of the respiratory effort waveform and generating slope values representative of the respiratory effort waveform based on the amplitude samples, and further wherein the detection of inspiration onset within the soft refractory period includes the step of detecting inspiration onset as a function of a comparison of the slope values to a predetermined slope value onset threshold and comparison of the amplitude thereof to a predetermined amplitude onset threshold.

12. The method according to claim 11, wherein the detection of inspiration onset within the soft refractory period includes detecting inspiration onset if a predetermined number of slope values satisfy the predetermined slope value onset threshold and the amplitude thereof satisfies the amplitude onset threshold.

13. The method according to claim 1, wherein the defining step includes the steps of:

detecting inspiration offset;

determining an average respiratory period;

providing an average time of inspiration; and

defining the refractory period, including the soft and hard refractory periods, as a function of the detected inspiration offset, average respiratory period, and average time of inspiration.

14. The method according to claim 13, wherein the refractory period is defined as a portion of the average respiratory period and the soft refractory period is defined as a portion of the refractory period.

15. The method according to claim 13, wherein the refractory period is defined as a portion of the average respiratory period and the soft refractory period is defined as a portion of the average respiratory period.

16. The method according to claim 13, wherein the average respiratory period is a weighted sum average respiratory period.

17. The method according to claim 1, wherein the refractory period is defined as a function of an average time of inspiration, the average time of inspiration being a physician programmable value.

18. The method according to claim 1, wherein the defining step includes defining the refractory period, including the soft and hard refractory periods, as a function of time of stimulation.

19. The method according to claim 2, wherein the monitoring step includes sampling the amplitude of the respiratory effort waveform and generating slope values representative of the respiratory effort waveform based on the amplitude samples, and further wherein the method includes setting an amplitude onset threshold and a slope value onset threshold, and yet further wherein the detection of inspiration onset outside of the refractory period is performed by comparing the slope values to the slope value onset threshold and the detection of inspiration onset within the soft refractory period is performed by comparing the slope values to the slope value onset threshold and the amplitude thereof to the amplitude onset threshold.

29. The method according to claim 1, wherein the monitoring step includes sampling the amplitude of the respiratory effort waveform signal and generating slope values representative of the respiratory effort waveform based on the amplitude samples, and further wherein the detection of inspiration onset within the soft refractory period includes the step of detecting inspiration onset as a function of a comparison of the slope values to a predetermined slope value onset threshold and comparison of the amplitude thereof to a predetermined amplitude onset threshold.

30. The method according to claim 29, wherein the detection of inspiration onset within the soft refractory period includes detecting inspiration onset if a predetermined number of slope values satisfy the predetermined slope value onset threshold and the amplitude thereof satisfies the amplitude onset threshold.

20. A method for providing stimulation of a patient to treat respiratory disorders, the method comprising the steps of:

monitoring slope and amplitude of a respiratory effort waveform of a patient to detect inspiration onset;

defining a refractory period including a hard refractory period during which time an inspiration onset cannot initiate stimulation and a soft refractory period following the hard refractory period;

detecting inspiration onset outside of the refractory period as a function of the slope of the respiratory effort waveform;

detecting inspiration onset within the soft refractory period as a function of slope and amplitude of the respiratory effort waveform; and

stimulating in response to a detected inspiration onset.

21. The method according to claim 20, wherein the refractory period is defined based on detection of inspiration offset.

22. The method according to claim 21, further including the step of detecting inspiration offset as a function of the monitored slope and amplitude of the respiratory effort waveform.

23. The method according to claim 22, wherein the monitoring step includes sampling the amplitude of the respiratory effort waveform and generating slope values representative of the respiratory effort waveform based on the amplitude samples, and further wherein the detection of inspiration offset includes the steps of:

comparing the slope values to a predetermined slope value offset threshold in a first comparison step;

comparing the amplitude of sampled respiratory effort waveform to a predetermined amplitude offset threshold in a second comparison step; and

detecting inspiration offset as a function of the first comparison step and the second comparison step.

24. The method according to claim 23, wherein the detection of inspiration offset further includes validating the detected inspiration offset by comparing the amplitude of the sampled respiratory waveform to a validating offset threshold and terminating stimulation as a function of such comparison.

25. The method according to claim 24, wherein the validating offset threshold is one of the detected inspiration offset, zero crossing of the respiratory waveform, or an inspiration onset threshold.

26. The method according to claim 23, wherein the detecting inspiration offset step further includes the step of detecting inspiration offset if a predetermined number of slope values satisfies the slope value offset threshold and the amplitude of at least the first of the predetermined number of slope values satisfies the amplitude offset threshold.

27. The method according to claim 20, wherein the monitoring step includes sampling the amplitude of the respiratory effort waveform signal and generating slope values representative of the respiratory effort waveform based on the amplitude samples, and further wherein the detection of inspiration onset outside of the refractory period includes the step of detecting an inspiration onset as a function of a comparison of the slope values to a predetermined slope value onset threshold.

28. The method according to claim 27, wherein the detection of inspiration onset outside of the refractory period includes detecting inspiration onset if a predetermined number of slope values satisfy the predetermined slope value onset threshold.

31. The method according to claim 20, wherein the defining step includes defining the refractory period, including the soft and hard refractory periods, as a function of time of stimulation.

32. The method according to claim 20, wherein the stimulation is continued until at least inspiration offset is detected or until a maximum stimulation time is reached.

33. A method for providing stimulation of a patient to treat respiratory disorders, the method comprising the steps of:

monitoring slope and amplitude of a respiratory effort waveform of a patient to detect inspiration onset and inspiration offset;

defining a refractory period including a hard refractory period during which time an inspiration onset cannot initiate stimulation and a soft refractory period following the hard refractory period;

detecting inspiration onset outside of the refractory period as a function of a first set of at least one of slope and amplitude criteria for the respiratory effort waveform;

detecting inspiration onset within the soft refractory period as a function of a second set of at least one of slope and amplitude criteria for the respiratory effort waveform;

stimulating in response to detection of inspiration onset, stimulation terminating as a function of detection of inspiration offset or a maximum stimulation time; and

setting the second set of criteria sufficiently sensitive relative to the first set of criteria such that stimulation, for one or more respiratory cycles, is applied as a function of the maximum stimulation time and the defined refractory period.

34. The method according to claim 33, further including the step of updating gain of the respiratory effort waveform during the one or more respiratory cycles such that stimulation can be controlled by detecting inspiration onset during later respiratory cycles.

35. A method of predicting critical points in patient respiration, the method comprising the steps of:

sampling the amplitude of the respiratory effort waveform of a patient;

generating a sample signal representative of at least one characteristic of the respiratory effort waveform based on each amplitude sample, monitoring the sample signals representative of the at least one characteristic of the respiratory effort waveform; and

detecting a respiratory event as a function of at least two sample signals.

36. The method according to claim 35, wherein the respiratory event is inspiration onset, and further wherein the at least one characteristic of the respiratory effort waveform is at least one of slope and amplitude.

37. The method according to claim 36, wherein inspiration onset is detected as a function of at least two sample signals representative of slope of the respiratory effort waveform.

38. The method according to claim 35, wherein the respiratory event is inspiration offset and further wherein the at least one characteristic of the respiratory effort waveform is at least one of slope and amplitude.

39. The method according to claim 38, wherein the generating step includes generating slope values representative of the respiratory effort waveform based on the each amplitude sample, and further wherein the detection of inspiration offset includes the steps of:

comparing the slope values to a predetermined slope value offset threshold in a first comparison step;

comparing the sampled amplitude of the respiratory effort waveform to a predetermined amplitude offset threshold in a second comparison step; and

detecting inspiration offset as a function of the first comparison step and the second comparison step.

40. The method according to claim 39, wherein the step of detecting inspiration offset further includes validating the detected inspiration offset by comparing the sampled amplitude of the respiratory waveform to a validating offset threshold, whereby the validated inspiration offset as opposed to the detected inspiration offset triggers an associated activity.

41. The method according to 40, wherein the validating offset threshold is one of the detected inspiration offset, zero crossing of the respiratory waveform, or an inspiration onset threshold.

42. The method according to claim 40, wherein the detecting inspiration offset step further includes the step of detecting inspiration offset if a predetermined number of slope values satisfies the slope value offset threshold and the amplitude of at least the first of the predetermined number of slope values satisfies the amplitude offset threshold.

43. An apparatus for predicting critical points in patient respiration, the apparatus comprising:

monitoring means for monitoring at least one characteristic of a respiratory effort waveform of a patient; and

respiration detection means for detecting a respiratory event, the respiration detection means including;

means for defining a refractory period including a hard refractory period and a soft refractory period following the hard refractory period;

means for detecting the respiratory event outside of the refractory period as a function of a first set of predetermined parameters for the monitored at least one characteristic of the respiratory effort waveform; and

means for detecting the respiratory event within the soft refractory period as a function of a second set of predetermined parameters for the monitored at least one characteristic of the respiratory effort waveform.

44. The apparatus according to claim 43, wherein the respiratory event is inspiration onset.

45. The apparatus according to claim 44, wherein the at least one characteristic of the respiratory effort waveform monitored is at least one of slope and amplitude of the respiratory effort waveform.

46. The apparatus according to claim 45, wherein the respiration detection means further includes means for detecting inspiration offset as a function of the at least one monitored slope and amplitude of the respiratory effort waveform.

47. The apparatus according to claim 46, wherein the inspiration offset detection means includes:

means for comparing the slope to a predetermined slope offset threshold; and

means for comparing the amplitude of the respiratory effort waveform to a predetermined amplitude offset threshold.

48. The apparatus according to claim 45, wherein the means for detecting the respiratory event outside of the refractory period includes means for comparing the monitored slope of the respiratory effort waveform to a predetermined slope onset threshold to detect inspiration onset.

49. The apparatus according to claim 45, wherein the means for detecting the respiratory event within the soft refractory period includes means for comparing the monitored slope of the respiratory effort waveform to a predetermined slope onset threshold and means for comparing the amplitude of the respiratory effort waveform to a predetermined amplitude onset threshold to detect inspiration onset.

50. A system for providing stimulation of a patient to treat respiratory disorders, the system comprising:

a sensor for providing a signal characteristic of a respiratory effort waveform of the patient;

slope monitoring means for monitoring the slope of the respiratory effort waveform;

amplitude monitoring means for monitoring the amplitude of the respiratory effort waveform;

respiration detection means for detecting inspiration onset, the respiration detection means including;

means for defining a refractory period, the refractory period including a hard refractory period during which time an inspiration onset cannot be responded to and a soft refractory period following the hard refractory period;

means for detecting inspiration onset outside of the refractory period as a function of the slope of the respiratory effort waveform;

means for detecting inspiration onset within the soft refractory period as a function of slope and amplitude of the respiratory effort waveform;

means for generating a stimulation signal in response to a detected inspiration onset; and

at least one electrode for delivering the stimulation signal to the patient.

51. The system according to claim 50, wherein the respiration detection means includes means for detecting inspiration offset as a function of at least one of monitored slope and amplitude, and further wherein the refractory period is defined based on detection of inspiration offset.

52. The system according to claim 50, wherein the means for detecting inspiration onset outside of the refractory period includes means for comparing the slope of the respiratory effort waveform to the predetermined slope onset threshold.

53. The system according to claim 51, wherein the means for detecting inspiration offset includes means for comparing the slope of the respiratory effort waveform to a predetermined slope offset threshold and means for comparing the amplitude of the respiratory effort waveform to a predetermined amplitude offset threshold.

54. The system according to claim 50, wherein the respiration detection means further includes means for terminating stimulation after a maximum predetermined stimulation time period.