FEATURE CHARACTERIZATION FOR BREATHING MONITOR

• US 20130331722A1
• Filed: 07/14/2011
• Published: 12/12/2013
• Est. Priority Date: 07/14/2010
• Status: Active Grant

• Current Assignee: Acurable Limited
• Original Assignee: Imperial Innovations Limited (Imperial College London)
• Inventors: Rodriguez-Villegas, Esther, Aguilar-Pelaez, Eduardo, Chen, Guangwei
• Granted Patent: US 10,226,225 B2
• Time in Patent Office: Days
• US Class Current: 600/529
• CPC Class Codes: A61B 2562/0219 Inertial sensors, e.g. accelerometers, gyroscopes, tilt switches
• CPC Class Codes: A61B 5/0022 Monitoring a patient using a global network, e.g. telephone networks, internet
• CPC Class Codes: A61B 5/08 Detecting, measuring or recording devices for evaluating the respiratory organs A61B5/0205 takes precedence
• CPC Class Codes: A61B 5/0816 Measuring devices for examining respiratory frequency measuring frequency of electric signals G01R23/00
• CPC Class Codes: A61B 5/0826 Detecting or evaluating apnoea events A61B5/4818 takes precedence
• CPC Class Codes: A61B 5/113 occurring during breathing
• CPC Class Codes: A61B 5/4836 Diagnosis combined with treatment in closed-loop systems or methods A61B5/0036 takes precedence
• CPC Class Codes: A61B 5/7282 Event detection, e.g. detecting unique waveforms indicative of a medical condition A61B5/4094, A61B5/4818, A61B5/349, A61B5/0823 take precedence
• CPC Class Codes: A61B 7/003 Detecting lung or respiration noise
• CPC Class Codes: A61B 7/04 Electric stethoscopes microphones, acoustic transducers therefor H04R
• CPC Class Codes: G16H 40/67 for remote operation

Abstract

A method of identifying a breath comprises sensing a signal generated by a living human or animal body and separating the signal into a plurality of frequency bands to identify a breath candidate.

Claims

1. A method of identifying a breath comprising:

sensing a signal generated by a living human or animal body; and

separating the signal into a plurality of frequency bands to identify a breath candidate.

2. A method as claimed in claim 1 further comprising applying a signal processing step to each separated band.

3. A method as claimed in claim 2 in which the signal processing step comprises at least one of subtracting an interference signal, scaling harmonics, delaying harmonics, filtering a DC signal, rectifying the signal, removing artifacts, smoothing the signal or filtering components above or below a frequency threshold.

4. A method as in claim 1 further comprising comparing frequency band values to identify candidate breath sounds.

5. A method as in claim 1 further comprising identifying a segment of a breath as either inspiration or expiration.

6. A method as claimed in claim 5 further comprising identifying a start point or an end point of an inspiration or expiration breath candidate by a process including the step of detecting as a signal feature a minimum or turning point or based on a previous end point or start point.

7. A method as claimed in claim 6 further comprising identifying the time at which the signal in at least one of the separated band has risen a predetermined proportion from a predetermined threshold.

8. A method as claimed in claim 7 in which the threshold in a separated band is dependent on at least a parameter of another separated band or on a previously used threshold.

9. A method as claimed in claim 7 in which the threshold is a function of a minimum or turning point.

10. A method as claimed in claim 1 further comprising identifying a signal noise floor.

11. A method as claimed in claim 10 further comprising identifying a respiratory pause and setting, as noise floor, the minimum of the signal value during the respiratory pause, for at least one separated band, or setting, as noise floor, the RMS value of the power of the signal integrated over a time within the respiratory pause.

12. A method as claimed in claim 11 comprising identifying a respiratory pause in each of a plurality of bands and setting a noise floor as a function of the noise floor of said plurality of bands.

13. A method as claimed in claim 10 further comprising establishing as noise floor a function of the noise floors estimated during several previously identified respiratory pauses, or dynamically updating the noise floor in one or several bands.

14. A method as claimed in claim 6 further comprising finding as a signal feature based on a maximum value of the signal in at least one separated band after a candidate start point of a possible inspiration or expiration has been found.

15. A method as claimed in claim 14 further comprising identifying said signal feature when the signal in at least one separated band has fallen a certain proportion from its respective maximum or identified, as said signal feature, the slope at that point.

16. A method as claimed in claim 15 in which the maximum is an absolute maximum in a candidate breath, or the slope value is the absolute slope.

17. A method as claimed in claim 15 further comprising identifying said signal feature as a second minimum.

18. A method as claimed in claim 14 further comprising identifying the time value of occurrence of a signal feature.

19. A method as claimed in claim 14 further comprising identifying for at least one separated band the duration of a possible expiratory or inspiratory phases from a measure of the difference between the time value of the first minimum and the time value when the signal has fallen a certain proportion from the respective maximum.

20. A method as claimed in claim 17 further comprising identifying the duration of a possible expiratory or inspiratory phase from a fraction of the absolute difference between a function of the time of the second minimum or a turning point and the time at which the signal has risen a certain proportion from a function of the first minimum or a turning point from at least one separated band, or comprising identifying as a candidate inspiration or expiration event the fraction of the signal between the function of said two minimums or turning points.

21. A method as claimed in claim 1 further comprising analyzing envelope characteristics of separated bands to identify a breath candidate, or comparing the values between identified minimum and said proportion of a maximum or proportional rise from a minimum.

22. A method as claimed in claim 21 further comprising identifying a degree of mathematic monotonicity of at least one separated band within a predetermined time.

23. A method as claimed in claim 21 further comprising identifying a breath candidate if a breath signal has a comparable envelope shape in two or more frequency bands.

24. A method as claimed in claim 22 further comprising using the monotonicity information to identify the intervals of time during which a search of minimums or maximums should take place.

25. A method as claimed in claim 11 further comprising measuring the signal-to-noise ratio for at least one separated band.

26. A method as claimed in claim 25 further comprising identifying an end point within the fraction of a segment for which the signal-to-noise ratio is above or below a certain threshold.

27. A method as claimed in claim 1 further comprising obtaining at least one functional relationship between equivalent parameters within separated bands.

28. A method as claimed in claim 27 in which the functional relationship is between values of a parameter of the processed signals which is correlated to power of the signal.

29. A method as claimed in claim 21 further comprising identifying the starting time of a candidate breath using the information about the monotonicity of one band, or the combined monotonicity of several bands and the minimum values of the processed signals in one or several bands.

30. A method as claimed in claim 27 further comprising comparing the values of the different relationships with a predetermined functional value, and identifying an event as a non-inspiration or non-expiration breath event if the comparison falls outside the predetermined value.

31. A method as claimed in claim 27 further comprising identifying, as a breath candidate, a breath signal having a parameter value greater than a proportion of the average value of preceding breath segments.

32. A method as claimed in claim 1 further comprising determining the number of breaths in a predetermined interval or the number of breaths having parameter values within a predetermined range for determination of a breathing condition.

33. A method as claimed in claim 32 further comprising detecting apnea if the number of breath candidates identified within a predetermined interval is lower than a predetermined threshold.

34. A method as claimed in claim 1 in which one or a plurality of measured parameters of at least one separated band is used to identify lung volume or respiratory rate related parameters.

35. A method as claimed in claim 1 further comprising determining a number of respiratory cycles in a predetermined interval based on a time location or separation of breath candidates in said interval for determination of respiratory rate.

36. A method as claimed in claim 35 further comprising generating an alarm if a proportion of the breath candidate detected in a certain time interval has measured characteristics that fall within predetermined critical limits.

37. A method as claimed in claim 1 comprising storing dynamically updating or reproducing signal, signal processing or signal analysis data or a unique person specific code, or reconstruction of signal data from a set of determined parameters.

39. A method as claimed in claim 1 further comprising confirming a sequence of breath candidates based on a comparison with an expected temporal distribution.

40. A method as claimed in claim 39 further comprising classifying an event as inspiration or expiration based on preceding inspirations or expiration patterns.

41. A method as claimed in claim 39 further comprising identifying an event as a candidate event if it deviates from previous candidate events patterns only within predetermined limits.

38. (canceled)

42. A breath detector comprising:

a signal detector; and

a signal processor configured to implement a method of identifying a breath, said method comprising sensing a signal generated by a living human or animal body and separating the signal into a plurality of frequency bands to identify a breath candidate.

43. A breath detector as claimed in claim 42 in which a sensor system is arranged to be attached to the body with an adhesive with an internal hole.

44. (canceled)

45. (canceled)

46. (canceled)