Method and apparatus for signal assessment including event rejection

• US 20060111642A1
• Filed: 11/22/2004
• Published: 05/25/2006
• Est. Priority Date: 11/22/2004
• Status: Active Grant

• Current Assignee: FUJIFILM SonoSite, Inc. (Fujifilm Holdings Corporation)
• Original Assignee: Sonosite Incorporated (Fujifilm Holdings Corporation)
• Inventors: Bouguerra, Radouane, Baura, Gail D., Malecha, Jeremy
• Granted Patent: US 7,570,989 B2
• Time in Patent Office: Days
• US Class Current: 600/513
• CPC Class Codes: A61B 5/029 Measuring or recording blood output from the heart, e.g. minute volume A61B8/065 takes precedence
• CPC Class Codes: A61B 5/0295 using plethysmography, i.e. measuring the variations in the volume of a body part as modified by the circulation of blood therethrough, e.g. impedance plethysmography
• CPC Class Codes: A61B 5/0535 Impedance plethysmography for measuring blood flow A61B5/0295
• CPC Class Codes: A61B 5/364 Detecting abnormal ECG interval, e.g. extrasystoles, ectopic heartbeats
• 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

Abstract

An improved method and apparatus for non-invasively assessing one or more physiologic parameters, such as for example those associated with the circulatory system of a living organism. In one exemplary embodiment, the invention evaluates cardiac events (e.g., beats) present within an ECG waveform to determine which beats should be retained and which rejected. This evaluation is conducted based on a hierarchical method, wherein the ECG noise and morphology, as well as various aspects of the Delta Z (change in thoracic impedance), are utilized to evaluate beats for retention/rejection. In one variant, fuzzy models are used in conducting the foregoing evaluations. Parameter median filtering is also optionally applied. The foregoing techniques increase the accuracy, stability and robustness of any systems (e.g., impedance cardiographic or otherwise) which make use of the events. Improved impedance cardiographic apparatus and methods of treatment are also disclosed.

Claims

1. A method of assessing cardiac output within a living subject, comprising:

disposing a plurality of electrodes relative to the thoracic cavity of said subject;

passing an electrical current through at least a portion of said thoracic cavity;

measuring at least one impedance waveform associated with said thoracic cavity using said current and at least one of said plurality of electrodes;

measuring at least electrocardiographic waveform having a plurality of events associated therewith;

selectively rejecting at least one of said events; and

determining cardiac output based at least in part on said impedance waveform and at least a portion of the non-rejected ones of said events.

2. The method of claim 1, further comprising processing said at least one impedance waveform to identify a plurality of B,C,X, and O points of Δ

Z and dZ/dt waveforms.

3. The method of claim 2, wherein the act of determining cardiac output comprises determining left ventricular ejection time (LVET).

4. The method of claim 3, wherein the act of determining LVET comprises determining the difference between respective ones of said plurality of X and B points.

5. The method of claim 1, wherein said events comprise cardiac beats, and said act of selectively rejecting at least one of said events comprises evaluating a plurality of said beats using a multi-level hierarchical analysis algorithm.

6. The method of claim 1, wherein said act of selectively rejecting at least one of said events comprises evaluating a plurality of cardiac beats based on (i) one or more ECG rejection criteria;

and (ii) one or more Delta Z rejection criteria.

7. The method of claim 6, further comprising evaluating said plurality of beats using at least one parameter median filter.

8. The method of claim 1, wherein said act of selectively rejecting at least one of said events comprises evaluating a plurality of said events based on criteria relating to (i) ECG noise, and (ii) ECG morphology.

9. The method of claim 8;

wherein said criteria relating to ECG noise comprises the change in the R-to-R interval from the previous beat.

10. The method of claim 9, wherein said criteria relating to ECG noise further comprises the change in mean squared error (MSE) from the last 2 good beats.

12. The method of claim 11, wherein the act of processing comprises evaluating said plurality of beats with respect to at least one noise criterion and at least one morphology criterion.

13. The method of claim 12, wherein said at least one noise criterion comprises a fuzzy logic analysis.

14. The method of claim 12, wherein said at least one noise and morphology criteria are conducted sequentially.

11. A method of assessing a hemodynamic parameter within a living subject, comprising:

disposing at least one electrode relative to said subject;

measuring at least one cardiographic waveform from said subject using said at least one electrode, said waveform having a plurality of beats;

processing said plurality of beats to identify first beats that should be rejected, and second beats that should not be rejected; and

assessing said hemodynamic parameter based at least in part on said second beats.

15. The method of claim 11, wherein said act of processing comprises generating a Scale 1 wavelet filter.

16. The method of claim 15, wherein said Scale 1 filter is calculated based on a reverse biorthogonal 2.2 wavelet.

17. Apparatus adapted to evaluate the cardiac beats of a living subject using at least one fuzzy-based noise algorithm and at least one fuzzy-based morphology algorithm.

18. The apparatus of claim 17, wherein said at least one morphology algorithm comprises generation of a Scale 1 wavelet filter.

19. The apparatus of claim 18, wherein said Scale 1 filter is calculated based on a reverse biorthogonal 2.2 wavelet.

20. Impedance cardiographic apparatus adapted to evaluate physiologic waveforms obtained from a living subject using a computer program adapted to evaluate criteria comprising (i) at least one ECG rejection criterion and (ii) at least one Delta Z rejection criterion.

21. The apparatus of claim 20, wherein said computer program comprises a fuzzy logic model adapted to perform said evaluation of said ECG rejection criterion.

22. The apparatus of claim 21, wherein said computer program comprises a fuzzy logic model adapted to perform said evaluation of said Delta Z rejection criterion.

23. The apparatus of claim 22, wherein said computer program is further adapted to apply median filtering to at least one parameter associated with said waveforms.

24. The apparatus of claim 20, wherein said apparatus is further adapted to receive at least one impedance waveform, and generate estimates of cardiac output (CO) based at least in part on said physiologic waveforms and said at least one impedance waveform.

25. The apparatus of claim 24, wherein said generation of estimates of CO is performed at least in part using wavelet transforms.

26. The apparatus of claim 25, wherein said wavelet transforms are used in detecting a plurality of fiducial points associated with at least one of said physiologic waveforms and said at least one impedance waveform.

27. The apparatus of claim 20, wherein said physiologic waveforms comprise ECG and impedance waveforms.

28. The apparatus of claim 27, wherein wavelet transforms are used in detecting a plurality of fiducial points associated with at least one of said physiologic waveforms.

29. Cardiographic apparatus adapted to evaluate the cardiac beats of a living subject using:

an ECG rejection analysis;

a Delta Z rejection analysis; and

a median filtering analysis.

30. The apparatus of claim 29, wherein said ECG rejection analysis comprises an ECG noise analysis and an ECG morphology analysis.

31. The apparatus of claim 29, wherein said Delta Z rejection analysis comprises an analysis selected from the group consisting of:

(i) a Delta Z similarity analysis and (ii) a Delta Z reproducibility analysis.

32. The apparatus of claim 30, wherein said Delta Z rejection analysis comprises an analysis selected from the group consisting of:

(i) a Delta Z similarity analysis and (ii) a Delta Z reproducibility analysis.

33. The apparatus of claim 29, wherein said ECG rejection, said Delta Z rejection, and said median filter analyses are performed in sequential order.

34. A method of evaluating the cardiac beats of a living subject, comprising:

performing an ECG rejection analysis;

performing a Delta Z rejection analysis; and

performing a median filtering analysis.

35. The method of claim 34, wherein said act of performing an ECG rejection analysis comprises performing an ECG noise analysis and an ECG morphology analysis.

36. The method of claim 34, wherein said act of performing a Delta Z rejection analysis comprises performing an analysis selected from the group consisting of:

(i) a Delta Z similarity analysis and (ii) a Delta Z reproducibility analysis.

37. The method of claim 35, wherein said act of performing a Delta Z rejection analysis comprises performing an analysis selected from the group consisting of:

(i) a Delta Z similarity analysis and (ii) a Delta Z reproducibility analysis.

38. A method of evaluating the cardiac beats of a living subject, comprising:

performing a beat rejection analysis on a plurality of said cardiac beats;

rejecting at least one of said beats as part of said analysis; and

determining, based at least in part on said at least one rejected beat, a status of said rejection analysis.

39. The method of claim 38, wherein said act of performing a beat rejection analysis comprises performing a morphology analysis.

40. The method of claim 39, wherein said act of determining a status comprises determining whether inputs to said morphology process are proper.

41. The method of claim 40, wherein said act of determining whether inputs to said morphology process are proper comprises evaluating the number of consecutive beat rejections including said at least one rejected beat.

42. The method of claim 41, wherein when said determination indicates that more than a predetermined number of consecutive beats has occurred, said method further comprises utilizing an automatic ECG vector process to identify at least one proper input.

43. A method of evaluating the cardiac beats of a living subject, comprising:

providing a plurality of sources of said cardiac beats;

performing a beat rejection analysis on a plurality of said cardiac beats derived from a first of said plurality of sources;

rejecting at least one of said beats as part of said analysis; and

determining, based at least in part on said at least one rejected beat, the suitability of said first source for providing said cardiac beats.

44. The method of claim 43, further comprising selecting a second of said sources as an input to said beat rejection analysis when said act of determining indicates that said first source is not suitable.

45. The method of claim 44, wherein said act of selecting comprises performing an auto-ECG vector analysis.

46. The method of claim 43, wherein said act of determining comprises evaluating at least one of (i) the number of consecutive beats rejected, and/or (ii) the number of resets of said beat rejection analysis previously performed.

47. The method of claim 46, further comprising selecting a second of said sources as an input to said beat rejection analysis when said act of determining indicates that said first source is not suitable.

48. The method of claim 47, wherein said act of selecting comprises performing an auto-ECG vector analysis.

49. Cardiographic apparatus having an ECG evaluation module and a plurality of input vectors associated therewith, said module evaluating the cardiac beats of a living subject represented by one or more of said vectors by the method comprising:

providing a plurality of sources of said cardiac beats;

performing a beat rejection analysis on a plurality of said cardiac beats derived from a first of said plurality of sources;

rejecting at least one of said beats as part of said analysis; and

determining, based at least in part on said at least one rejected beat, the suitability of said first source for providing said cardiac beats.

50. A method of evaluating substantially periodic events within a time-variant waveform, comprising:

providing a plurality of sources of said events;

performing an event rejection analysis on a plurality of said events derived from a first of said plurality of sources;

rejecting at least one of said events as part of said analysis; and

determining, based at least in part on said at least one rejected event, the suitability of said first source for providing said events.

51. The method of claim 50, wherein said events comprise Gaussian monopulses within a time-modulated ultrawideband communication system.

52. The method of claim 50, wherein said events comprise active acoustic pulses within a sonar or underwater acoustic profiling system.