Automated auscultation system

• US 20040260188A1
• Filed: 06/17/2003
• Published: 12/23/2004
• Est. Priority Date: 06/17/2003
• Status: Abandoned Application

• Current Assignee: Massachusetts Institute of Technology, The General Hospital Corporation (Mass General Brigham, Inc.)
• Original Assignee: Massachusetts Institute of Technology, The General Hospital Corporation (Mass General Brigham, Inc.)
• Inventors: Syed, Zeeshan Hassan, Nesta, Francesca, Guttag, John, Curtis, Dorothy, Levine, Robert A.
• Application Number:
  US10/464,267
• Publication Number:
  US 20040260188A1
• Time in Patent Office: Days
• US Class Current: 600/509
• CPC Class Codes: A61B 5/352 Detecting R peaks, e.g. for synchronising diagnostic apparatus; Estimating R-R interval
• CPC Class Codes: A61B 5/4884 inducing physiological or psychological stress, e.g. applications for stress testing
• CPC Class Codes: A61B 5/7203 for noise prevention, reduction or removal
• CPC Class Codes: A61B 5/726 using Wavelet transforms
• 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: A61B 7/00 Instruments for auscultation
• CPC Class Codes: A61B 7/04 Electric stethoscopes microphones, acoustic transducers therefor H04R

Abstract

The present invention provides systems and methods for performing automated auscultation and diagnosis of conditions of the cardiovascular system. The invention acquires an acoustic signal emanating from the cardiovascular system via an sensor. In addition, in certain embodiments of the invention an electrical signal, e.g., an electrocardiogram (EKG) is simultaneously acquired. The signals are digitized, and, optionally, filtered to remove noise. The invention then processes and analyses the signal(s) so as to provide a clinically relevant conclusion or recommendation such as a diagnosis or suggested additional tests or therapy. In preferred embodiments the system comprises: (1) a beat selection component that selects a plurality of beats for analysis, wherein each beat comprises an acoustic signal emanating from the cardiovascular system; (2) a time-frequency analysis component that performs a time-frequency decomposition of beats selected for analysis so as to identify or extract physiologically relevant features; and (3) a processing component that processes the information so at to provide a clinically relevant conclusion or recommendation. In preferred embodiments of the invention the system further includes an aggregation component that combines information obtained from a plurality of the beats selected for analysis. In one embodiment, the system diagnoses mitral valve prolapse.

Claims

1. A method of performing automated auscultation of the cardiovascular system, the method comprising steps of:

(a) selecting one or more beats for analysis, wherein each beat comprises an acoustic signal emanating from the cardiovascular system;

(b) performing a time-frequency analysis of beats selected for analysis so as to provide information regarding the distribution of energy, the relative distribution of energy, or both, over different frequency ranges at one or more points in the cardiac cycle; and

(c) processing the information to reach a clinically relevant conclusion or recommendation; and

(d) presenting some or all of the information in a manner that facilitates a mechanistically comprehensible explanation of the basis for the conclusion or recommendation or how the conclusion or recommendation was reached.

2. The method of claim 1, further comprising:

providing a mechanistically comprehensible explanation of the basis for the conclusion or recommendation or of how the conclusion or recommendation was reached.

3. The method of claim 1, wherein the step of selecting one or more beats for analysis is performed automatically.

4. The method of claim 1, wherein more than one beat is selected for analysis.

5. The method of claim 1, wherein performing a time-frequency analysis comprises performing a time-frequency decomposition.

6. The method of claim 1, further comprising the step of:

combining information obtained from a plurality of the beats selected for analysis prior to the step of processing the information to reach a clinically relevant conclusion or recommendation.

7. The method of claim 1, further comprising the step of:

outputting the clinical conclusion or recommendation together with one or more of the following;

a display of at least a portion of the acoustic signal, a display of an annotated or unannotated EKG tracing, a display of a frequency decomposed acoustic signal representing one or more beats, one or more enhanced beats, or a prototypical beat, and an audio playback of one or more beats or a prototypical beat.

8. The method of claim 7, wherein the clinical conclusion or recommendation is selected from the group consisting of:

whether a pathological condition exists, whether a benign condition exists, whether to make a referral to a specialist, whether to perform an additional diagnostic study, and whether to initiate or alter therapy.

9. A method of performing automated auscultation of the cardiovascular system, the method comprising steps of:

(a) selecting one or more beats for analysis, wherein each beat comprises an acoustic signal emanating from the cardiovascular system;

(b) performing a time-frequency analysis of beats selected for analysis so as to provide information regarding the distribution of energy, the relative distribution of energy, or both, over different frequency ranges at one or more points in the cardiac cycle;

(c) combining information obtained from a plurality of the beats selected for analysis; and

(d) processing the information to reach a clinically relevant conclusion or recommendation,

wherein the step of performing a time-frequency analysis, the processing step, or both make use of knowledge of the physiological or mechanistic basis of a disease or clinical condition of the cardiovascular system.

10. The method of claim 9, wherein performing a time-frequency analysis comprises performing a time-frequency decomposition.

11. A method of performing automated auscultation of the cardiovascular system of a subject, the method comprising steps of:

(a) selecting one or more beats for analysis, wherein each beat comprises an acoustic signal emanating from the cardiovascular system;

(b) performing a time-frequency analysis of beats selected for analysis so as to provide information regarding the distribution of energy, the relative distribution of energy, or both, over different frequency ranges at one or more points in the cardiac cycle;

(c) if more than one beat was selected in step (a), combining information obtained from a plurality of the beats selected for analysis; and

(d) processing the information to reach a clinically relevant conclusion or recommendation.

12. The method of claim 11, wherein more than one beat is selected.

13. The method of claim 11, wherein the one or more beats are selected automatically.

14. The method of claim 11, wherein the step of selecting one or more beats for analysis comprises:

segmenting the acoustic signal representing a beat into regions of interest by locating the position of at least the second heart sound within the acoustic signal, wherein the second heart sound associated with that beat is located by searching over a predetermined time interval following the peak in the T wave for that beat and declaring the position of the second heart sound to be at the position of the peak in the acoustic signal within the predetermined time interval.

15. The method of claim 14, wherein the T wave for a beat is declared to be at the position of the peak in the EKG signal within an interval beginning a predetermined period of time following the QRS complex for that beat and within a predetermined fraction of the cardiac cycle immediately following the QRS complex for that beat.

16. The method of claim 15, wherein the second heart sound associated with a beat is located by searching over a predetermined time interval following the peak in the T wave for the beat and declaring the position of the second heart sound for the beat to be at the position of the peak in the acoustic signal within the predetermined time interval.

17. The method of claim 15, wherein the second heart sound associated with a beat is located by:

(a) initially searching over a predetermined time interval following the peak in the T wave for each of a plurality of beats and declaring the position of the second heart sound for each beat to be at the position of the peak in the acoustic signal within the predetermined time interval;

(b) computing the systolic length for the plurality of beats using the positions of the second heart sounds located in step (a) and the positions of the corresponding QRS complexes or the corresponding first heart sounds;

(c) computing the median systolic length for the plurality of beats; and

(d) determining the position of the second heart sound for a beat by adding the median systolic length computed in step (c) to the position of the QRS complex or first heart sound corresponding to that beat.

18. The method of claim 11, wherein the step of selecting one or more beats for analysis comprises:

segmenting the acoustic signal into regions of interest using information obtained from an EKG, wherein the regions of interest are systolic regions or diastolic regions; and

discarding as too noisy those beats wherein the peak amplitude of the acoustic signal within the region of interest is greater than the amplitude of either the first or second heart sound or both.

19. The method of claim 11, wherein the step of selecting one or more beats for analysis comprises:

segmenting the acoustic signal into regions of interest using information obtained from an EKG, wherein the regions of interest are systolic regions or diastolic regions;

discarding those beats deemed too noisy; and

retaining a subset of the remaining beats based on their length.

20. The method of claim 19, wherein the retaining step is biased in favor of retaining longer beats.

21. The method of claim 19, wherein the retaining step is biased in favor of retaining shorter beats.

22. The method of claim 19, wherein the retaining step comprises:

(a) computing the median and standard deviation of the lengths of the remaining beats;

(b) computing values for either an upper threshold, a lower threshold, or both, wherein the value of an upper threshold is computed by adding a first predetermined percentage of the standard deviation to the median length, and a value for the lower threshold is computed by subtracting a second predetermined percentage of the standard deviation from the median length; and

(c) retaining beats whose length is greater than the lower threshold or is less than the upper threshold or falls within the interval between the upper and lower thresholds.

23. The method of claim 22, wherein the first and second predetermined percentages are the same.

24. The method of claim 22, wherein the first and second predetermined percentages are different.

25. The method of claim 22, further comprising the steps of:

(d) computing values for either a second upper threshold, a second lower threshold, or both, wherein the value of the second upper threshold is computed by adding a third predetermined percentage of the standard deviation to the upper threshold computed in step (b), and a value for the second lower threshold is computed by subtracting a fourth predetermined percentage of the standard deviation from the lower threshold computed in step (b); and

(e) retaining beats whose length is greater than the second lower threshold or is less than the second upper threshold or falls within the interval between the second upper and second lower thresholds.

26. The method of claim 25, wherein the third and fourth predetermined percentages are the same.

27. The method of claim 25, wherein the third and fourth predetermined percentages are different.

28. The method of claim 11, wherein performing a time-frequency analysis comprises performing a time-frequency decomposition.

29. The method of claim 28, wherein the time-frequency decomposition is performed by subjecting the acoustic signal to analysis by a filter bank comprising a plurality of frequency filters that separate the acoustic signal into its components within a plurality of frequency bands.

30. The method of claim 28, wherein the frequency filters have sufficient sharpness so as to substantially eliminate overlap between the frequency bands that they span.

31. The method of claim 28, wherein the frequency filter for each frequency band has a transition band width significantly lower than the width of adjacent frequency bands such that the energy content of the signal passed by each frequency filter is substantially free of energy contributed by signal from neighboring frequency bands.

32. The method of claim 31, wherein the transition bands of the frequency filters have widths less than approximately 10% of the widths of their passbands and the passbands of adjacent frequency filters.

33. The method of claim 28, wherein the frequency filters implement a finite impulse response approximation to the infinite impulse response of an ideal filter.

34. The method of claim 11, wherein the time-frequency analysis separates the acoustic signal into its components within a plurality of initial frequency bands, further comprising the step of aggregating multiple adjacent members of the plurality of initial frequency bands so as to create a set of broader composite frequency bands.

35. The method of claim 34, wherein the initial frequency bands are normalized prior to aggregation.

36. The method of claim 34, further comprising the step of taking the absolute value of the amplitudes of the signal in each initial frequency band prior to performing aggregation of the initial frequency bands.

37. The method of claim 11, wherein the step of selecting a plurality of beats for analysis is performed automatically.

38. The method of claim 11, wherein the time-frequency analysis separates the acoustic signal into its components within a plurality of frequency bands, and wherein the combining step creates a prototypical beat by, for each frequency band, aligning a plurality of beats in time, identifying a median set of amplitudes at each time instant for each of the frequency bands, wherein the median set consists of a predetermined number of amplitudes;

and computing the mean of each median set, thereby obtaining a time-frequency decomposition of a prototypical beat.

39. The method of claim 11, wherein the time-frequency analysis separates the acoustic signal into its components within a plurality of initial frequency bands, and wherein the processing step comprises identifying one or more points in the cardiac cycle at which the distribution of energy at in at least one of the frequency bands or in a composite frequency band created by aggregating multiple adjacent initial frequency bands differs from the distribution of energy expected to be present in a normal subject or determining whether such a point or points exist.

40. The method of claim 11, wherein the processing step comprises computing one or more time metrics, amplitude metrics, or both, that characterize the distribution of energy at one or more points in the cardiac cycle in at least one of the frequency bands.

41. The method of claim 11, wherein the processing step comprises applying band-specific thresholding to one or more frequency bands.

42. The method of claim 41, wherein the step of applying band-specific thresholding comprises:

(a) identifying the point of maximum signal amplitude within a region of interest for one or more of the frequency bands;

(b) calculating the earliest point in the region of interest where the signal amplitude first exceeds a predetermined percentage of the maximum signal amplitude for the one or more frequency bands;

(c) for each point calculated in step (b), computing the time interval between the point calculated in step (b) and a second time point;

(d) scaling the time interval(s) computed in step (c) by the length of the region of interest; and

(e) comparing the scaled time interval(s) computed in step (d) with a predetermined value, thereby determining whether to classify the acoustic signal as indicative of the existence or severity of a clinical condition.

43. The method of claim 42, wherein the predetermined value differs for different frequency bands.

44. The method of claim 42, wherein the region of interest is the second half of systole, and the second time point is the time point at which S2 occurs.

45. The method of claim 39, 40, 41, or 42, wherein the processing step comprises:

identifying each beat as normal or as indicative of the existence or severity of a clinical condition; and

concluding that the subject has the clinical condition if a predetermined percentage of the beats indicate the existence or severity of the condition.

46. The method of claim 39, 40, 41, or 42, wherein the system creates a prototypical beat, and wherein the analyzing step comprises identifying the prototypical beat as normal or as indicative of the existence or severity of a clinical condition.

47. The method of claim 11, further comprising the step of:

outputting the clinical conclusion or recommendation.

48. The method of claim 47, further comprising outputting one or more of the following together with the clinical conclusion or recommendation:

a display of at least a portion of the acoustic signal, a display of an EKG tracing, a display of a frequency decomposed acoustic signal representing one or more beats or a prototypical beat, and an audio playback of one or more beats or a prototypical beat.

49. The method of claim 48, wherein any of the displays may be annotated or unannotated.

50. The method of claim 47, wherein the clinical conclusion or recommendation is selected from the group consisting of:

whether a pathological condition exists, whether a benign condition exists, the likelihood that a pathological condition exists, the likelihood that a benign condition exists, the identity of a pathological or benign condition that the subject may have, the qualitative or quantitative severity of a clinical condition, whether to make a referral to a specialist, whether to perform an additional diagnostic study, and whether to initiate or alter therapy.

51. The method of claim 50, wherein the condition is mitral valve prolapse.

52. The method of claim 51, wherein the system determines whether the subject has mitral valve prolapse.

53. The method of claim 50 or 51, wherein the system identifies regurgitant and non-regurgitant mitral valve prolapse.

54. A method of performing automated auscultation of the cardiovascular system, the method comprising steps of:

(a) selecting a plurality of beats;

(b) constructing a prototypical beat by combining information from the plurality of beats;

(c) computing a metric that characterizes the prototypical beat; and

(d) classifying the prototypical beat as indicative of the presence or absence of a disease or condition, or of its severity, by comparing the metric computed in step (c) with a value for the metric characteristic of a normal subject.

55. The method of claim 54, wherein the information comprises a time-frequency decomposition of each of the plurality of beats.

56. The method of claim 54, wherein the metric reflects the distribution, relative distribution, or both of energy in one or more frequency bands for the prototypical beat.

57. A method of performing automated auscultation of the cardiovascular system, the method comprising steps of:

(a) selecting a plurality of beats;

(b) constructing a prototypical beat by combining information from the plurality of beats; and

(c) presenting the prototypical beat, a time-frequency decomposition of the prototypical beat, or both, to a user, wherein presenting the prototypical beat comprises displaying an image of the beat, playing a recording of the beat or an enhanced version thereof, or both.

58. A method of performing automated auscultation of the cardiovascular system, the method comprising steps of:

(a) selecting one or more beats for analysis, wherein each beat comprises an acoustic signal emanating from the cardiovascular system;

(b) performing a time-frequency analysis of beats selected for analysis so as to provide information regarding the distribution of energy, the relative distribution of energy, or both, over different frequency ranges at one or more points in the cardiac cycle; and

(c) presenting information derived at least in part from the acoustic signal, wherein the information comprises one or more items selected from the group consisting of;

a visual or audio presentation of a prototypical beat, a display of the time-frequency decomposition of one or more beats or prototypical beats, and a playback of the acoustic signal at a reduced rate with preservation of frequency content, wherein any of the foregoing items may be annotated or unannotated.

59. A system for performing automated auscultation of the cardiovascular system, the system comprising:

(a) a beat selection component that selects one or more beats for analysis, wherein each beat comprises an acoustic signal emanating from the cardiovascular system;

(b) a time-frequency analysis component that provides information regarding the distribution of energy, the relative distribution of energy, or both, over different frequency ranges at one or more points in the cardiac cycle; and

(c) a diagnostic module that processes the information to as to reach a clinically relevant conclusion or recommendation; and

(d) a presentation component that presents some or all of the information in a manner that facilitates a mechanistically comprehensible explanation of the basis for the conclusion or recommendation or how the conclusion or recommendation was reached.

61. The system of claim 59 or 60, wherein the beat selection component selects beats automatically.

62. The system of claim 59 or 60, wherein the time-frequency analysis component comprises a time-frequency decomposition component.

63. The system of claim 59, further comprising:

an aggregation component that combines information obtained from a plurality of the beats selected for analysis.

69. The system of claim 67 or 68, wherein the apparatus for performing automated auscultation is as described in claim 59.

60. A system for performing automated auscultation of the cardiovascular system of a subject, the method comprising steps of:

(a) a beat selection component that selects one or more beats for analysis, wherein each beat comprises an acoustic signal emanating from the cardiovascular system;

(b) a time-frequency analysis component that performs a time-frequency analysis of beats selected for analysis so as to provide information regarding the distribution of energy, the relative distribution of energy, or both, over different frequency ranges at one or more points in the cardiac cycle;

(c) an aggregation component that combines information obtained from a plurality of the beats selected for analysis; and

(d) a diagnostic module that processes the information to reach a clinically relevant conclusion or recommendation.

64. The system of claim 60 or 63, further comprising one or more sensors that acquire the acoustic signal, an EKG, or both.

65. The system of claim 60 or 63, further comprising an electronic stethoscope comprising one or more sensors that acquire the acoustic signal, the EKG, or both.

66. The system of either claim 64 or 65, wherein the acoustic signal, the EKG, or both are transmitted wirelessly to a computing device.

67. A system for assisting in the clinical evaluation of a subject'"'"'s cardiovascular system comprising:

an apparatus for performing automated auscultation of the cardiovascular system of a subject, wherein the apparatus analyzes an acoustic signal emanating from the cardiovascular system and provides a clinically relevant conclusion or recommendation; and

at least one audio-visual diagnostic aid that presents information derived at least in part from the acoustic signal.

70. The system of claim 67, wherein the audio-visual diagnostic aid presents information that directly reflects the mechanistic basis upon which the apparatus reached the clinically relevant conclusion or recommendation.

71. The system of claim 67, wherein the audio-visual diagnostic aid displays and/or plays back a prototypical acoustic signal obtained by aggregating information from a plurality of the subject'"'"'s heart beats.

72. The system of claim 71, wherein the prototypical acoustic signal is enhanced to emphasize features of diagnostic significance.

73. The system of claim 67, wherein the audio-visual diagnostic aid additionally displays at least a portion of an EKG obtained from the subject, which EKG may be annotated and may be aligned with a display of an acoustic signal.

74. The system of claim 67, wherein the audio-visual diagnostic aid provides playback of the acoustic signal at a reduced rate with preservation of frequency content.

75. The system of claim 67, wherein the apparatus performs a time-frequency decomposition of the acoustic signal, and wherein the audio-visual diagnostic aid displays the time-frequency decomposition by separately displaying frequency components in a plurality of different frequency ranges.

68. A system for assisting in the clinical evaluation of a subject'"'"'s cardiovascular system comprising:

an apparatus for performing automated auscultation of the cardiovascular system of a subject; and

at least one audio-visual diagnostic aid that presents information derived at least in part from the acoustic signal, wherein the information comprises one or more items selected from the group consisting of;

a visual or audio presentation of a prototypical beat, a display of the time-frequency decomposition of one or more beats or prototypical beats, and a playback of the acoustic signal at a reduced rate with preservation of frequency content, wherein any of the foregoing items may be annotated or unannotated.