Method and apparatus for hemodynamic assessment including fiducial point detection
First Claim
1. A method of assessing cardiac output within a living subject, comprising:
- providing a plurality of electrodes disposed 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;
processing said at least one impedance waveform using discrete wavelet transforms to identify one or more fiducial points within said at least one impedance waveform; and
determining cardiac output based at least in part on said one or more fiducial points.
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Abstract
An improved method and apparatus for non-invasively assessing one or more hemodynamic parameters associated with the circulatory system of a living organism. In one exemplary embodiment, the invention comprises a method of measuring cardiac output (CO) using impedance waveforms (and ECG waveforms) which are analyzed via discrete wavelet transforms. These transforms aid in identifying fiducial points within the waveforms, the fiducial points being used to calculate various parameters relating to cardiac stroke volume (such as LVET and dZ/dtmax), from which cardiac output may be determined. The use of wavelet transforms for fiducial point detection increases the accuracy of the CO determination by reducing cross-term artifact, and also significantly reduces the amount and complexity of processing required as compared to prior art time-frequency distribution or empirical techniques. Improved methods of QRS complex detection within the ECG waveform, and median filtering of an input waveform, are also disclosed.
292 Citations
46 Claims
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1. A method of assessing cardiac output within a living subject, comprising:
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providing a plurality of electrodes disposed 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;
processing said at least one impedance waveform using discrete wavelet transforms to identify one or more fiducial points within said at least one impedance waveform; and
determining cardiac output based at least in part on said one or more fiducial points. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
determining the magnitude of the largest negative derivative of the impedance change occurring during systole (dZ/dtmax) from said C point;
determining the stroke volume from at least LVET and dZ/dtmax; and
determining cardiac output based at least in part on said stroke volume.
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6. The method of claim 2, wherein said act of identifying said plurality of B, C, X, and O points comprises detecting at least one C point using a Mallet scaling filter, mA(k).
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7. The method of claim 2, wherein said act of identifying said plurality of B, C, X, and O points comprises detecting at least one B point using scale 2 detail coefficients of Δ
- Z, using a Symlet2 scaling filter, sA(k), and wavelet filter, SD(k).
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8. The method of claim 7, wherein said act of identifying said plurality of B, C, X, and O points comprises detecting at least one B point using scale 2 detail coefficients of Δ
- Z, using a Symlet2, scaling filter, sA(k), and wavelet filter, sD(k).
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9. The method of claim 2, wherein said act of identifying said plurality of B, C, X, and O points comprises detecting at least one X point using scale 1 approximation coefficients of dZ/dt based on a fiducial filter, fA(k).
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10. A method of assessing a hemodynamic parameter within a living subject, comprising:
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disposing a plurality of electrodes relative to said subject;
measuring at least one impedance waveform from said subject using at least one of said plurality of electrodes;
processing said at least one impedance waveform using at least one wavelet transform to identify one or more fiducial points within said at least one impedance waveform; and
assessing said hemodynamic parameter based at least in part on the one or more of said fiducial points. - View Dependent Claims (11, 12, 13, 14)
determining the magnitude of the largest negative derivative of the impedance change occurring during systole (dZ/dtmax) from the C point; and
determining the stroke volume from at least LVET and dZ/dtmax.
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15. A method of detecting events within the electrocardiogram (ECG) of a living subject, comprising:
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disposing at least one electrode relative to the thoracic cavity of said subject;
measuring at least one ECG waveform using said at least one electrode; and
processing said at least one ECG waveform using discrete wavelet transforms to identify one or more events within said ECG waveform. - View Dependent Claims (16, 17, 18, 19)
identifying at least one QRS complex based at least in part on said one or more fiducial points; and
identifying beats based at least in part on said at least one QRS complex.
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17. The method of claim 16, further comprising:
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detecting the R point in said at least one QRS complex; and
detecting the onset of depolarization of said QRS complex (Q point) in said at least one complex.
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18. The method of claim 17, wherein the act of detecting at least one QRS complex comprises determining the detail coefficients using a Haar wavelet transform pair.
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19. The method of claim 18, wherein the act of determining the detail coefficients using a Haar wavelet transform comprises determining the scale 1 and scale 2 detail coefficients.
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20. An information storage device, comprising;
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a data storage medium;
a plurality of data stored on said medium, said plurality of data comprising a computer program adapted to run on a data processor, said computer program being configured for determining at least one value of a first hemodynamic parameter of a living subject based on first input data and second input data, said first input data being representative of an impedance waveform, said second input data being representative of a an electrocardiographic (ECG) waveform, the act of determining said at least one value of said first hemodynamic parameter comprising;
processing said at least one impedance waveform using wavelet transforms to identify at least one fiducial point therein;
processing said at least one ECG waveform using wavelet transforms to identify at least one fiducial point therein; and
determining said at least one value of said first hemodynamic parameter based at least in part on said at least one fiducial points from said impedance and ECG waveforms, respectively. - View Dependent Claims (21, 22, 23)
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24. Apparatus for assessing at least one hemodynamic parameter associated with a living subject comprising;
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a plurality of electrodes adapted to be disposed in proximity to the thoracic cavity of the subject;
a current source adapted to provide an electrical current through at least a portion of said thoracic cavity via at least a first of said plurality of electrodes, and produce an impedance waveform relating thereto on at least a second of said plurality of electrodes; and
a signal processing apparatus, operatively coupled to said at least second of said plurality of electrodes, said signal processing apparatus adapted to analyze said impedance waveform using wavelet transforms to assess said at least one hemodynamic parameter. - View Dependent Claims (25, 26, 27, 28, 29, 30, 31)
signal conditioning apparatus adapted to condition at least said impedance waveform;
an analog-to-digital converter to convert at least a portion of said impedance waveform to binary digital format data; and
a digital processor adapted to run at least one computer program thereon, said at least one computer program being configured to calculate at least one wavelet transform based on said binary digital format data.
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29. The apparatus of claim 28, wherein said digital processor comprises a digital signal processor (DSP), and at least a portion of said computer is disposed within an embedded memory associated therewith.
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30. The apparatus of claim 27, wherein said signal processing apparatus is adapted to identify at least one QRS complex using said wavelet transforms.
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31. The apparatus of claim 27, wherein said signal processing apparatus is adapted to identify at least one Q point within said ECG waveform, said analysis of said impedance waveform using wavelet transforms being dependent at least in part upon said at least one Q point.
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32. A signal processing apparatus adapted for analyzing waveforms obtained from a living subject, comprising:
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an analog-to-digital converter to convert at least a portion of said waveforms to binary digital format data; and
a digital processor adapted to run at least one computer program thereon, said at least one computer program being configured to calculate at least one wavelet transform based on said binary digital format data. - View Dependent Claims (33, 34, 35, 36, 37, 38)
(i) band pass filtering; and
(ii) decimation.
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35. The apparatus of claim 32, wherein said at least one computer program is adapted to:
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identify, using at least one wavelet transform, the B, C, O, and X points within an impedance waveform; and
identify, using at least one wavelet transform, at least one QRS complex within an ECG waveform.
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36. The apparatus of claim 35, wherein said C point is detected using a Mallet scaling filter, mA(k).
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37. The method of claim 35, wherein said B point is detected using scale 2 detail coefficients of Δ
- Z based on a Symlet2 scaling filter, sA(k), and wavelet filter, sD(k).
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38. The method of claim 35, wherein said X point is detected using scale 1 approximation coefficients of dZ/dt based on a fiducial filter, fA(k).
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39. A method of providing treatment to a living subject, comprising:
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disposing a plurality of electrodes with respect to the thoracic cavity of said subject;
measuring at least one impedance waveform via at least one of said plurality of electrodes;
measuring at least one ECG waveform via at least one of said plurality of electrodes;
determining the stroke volume of the subject'"'"'s heart using at least one discrete wavelet transform; and
providing treatment to the subject based on the determined cardiac stroke volume. - View Dependent Claims (40, 41, 42)
(i) detecting one or more fiducial points within said at least one impedance waveform using wavelet transforms; and
(ii) detecting one or more QRS complexes within said at least one ECG waveform.
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41. The method of claim 40, wherein the act of determining stroke volume further comprises detecting one or more fiducial points within said at least one ECG waveform.
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42. The method of claim 40, wherein the act of detecting one or more QRS complexes comprises detecting said one or more QRS complexes using a Haar wavelet transform.
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43. A method of assessing cardiac output within a living subject, comprising the steps of:
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disposing a plurality of electrodes disposed relative to the thoracic cavity of said subject for detecting electrical signals therefrom;
passing an electrical current through at least a portion of said thoracic cavity to permit measurement of at least one impedance waveform associated therewith;
measuring said at least one impedance waveform;
processing said at least one impedance waveform using discrete wavelet transforms for identification one or more fiducial points within said at least one impedance waveform; and
determining cardiac output based at least in part on said one or more fiducial points.
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44. A method of filtering a cardiac impedance (Z) waveform having a plurality of cardiac beats, comprising:
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selecting a beat average;
calculating a first value of at least one parameter associated with said impedance waveform;
buffering said first value in at least one median filter, said at least one median filter being adapted to permit shifting with each successive one of said plurality of beats;
calculating a second value of at least one parameter associated with said impedance waveform;
buffering said second value in said at least one median filter; and
calculating a median value for said at least one parameter based at least in part on said first and second values and said beat average.
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45. Apparatus useful for assessing at least one hemodynamic parameter associated with a living subject comprising;
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at least one electrical pathway adapted for signal communication with a monitoring system, said monitoring system comprising;
a plurality of electrodes adapted for use proximate the thoracic cavity of said living subject; and
a current source adapted to provide an electrical current through at least a portion of said thoracic cavity via at least a first of said plurality of electrodes, and produce an impedance waveform relating thereto on at least a second of said plurality of electrodes, wherein said at least second electrode of said plurality is in signal communication with said at least one electrical pathway; and
a signal processing apparatus, operatively coupled to said at least one electrical pathway, said signal processing apparatus adapted to analyze said impedance waveform using wavelet transforms to assess said at least one hemodynamic parameter. - View Dependent Claims (46)
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Specification