Non-invasive monitoring of hemodynamic parameters using impedance cardiography
First Claim
1. A method for processing a bioimpedance signal of a patient for derivation of heart rate, heart stroke volume, and cardiac output comprising:
- digitally filtering and phase correcting the bioimpedance signal to remove gain-phase-frequency distortions;
estimating heart rate using a power spectrum of the bioimpedance signal, and an auto-convolution function of the said power spectrum;
suppressing breath waves to remove undesired power spectra components and generate a bioimpedance signal of restored shape;
determining cardiocycles of said restored bioimpedance signal;
determining effective left ventricular ejection time (ELVET) using check points within said cardiocycles; and
discarding at least some of said cardiocycles which exhibit interference artifacts.
1 Assignment
0 Petitions
Accused Products
Abstract
A method and apparatus for determination of heart rate, heart stroke volume, and cardiac output from thoracic bioimpedance signals. A unique bioimpedance electrode arrangement is employed, and the bioimpedance signals are corrected for gain-phase-frequency distortion through the use of sinusoidal test signals through the measuring or detection electrodes to identify distortions and correct for same during actual measurements. Time-derivative bioimpedance signals are employed, the power spectrum calculated, and a novel autoconvolution procedure used to emphasize the heart rate harmonic. Breath waves and other signals not indicative of the patient'"'"'s cardiocycles are removed. Left ventricular ejection time is derived from the bioimpedance signals, and an improved version of Kubicek'"'"'s equation is employed to derive heart stroke volume and thus cardiac output.
167 Citations
25 Claims
-
1. A method for processing a bioimpedance signal of a patient for derivation of heart rate, heart stroke volume, and cardiac output comprising:
-
digitally filtering and phase correcting the bioimpedance signal to remove gain-phase-frequency distortions; estimating heart rate using a power spectrum of the bioimpedance signal, and an auto-convolution function of the said power spectrum; suppressing breath waves to remove undesired power spectra components and generate a bioimpedance signal of restored shape; determining cardiocycles of said restored bioimpedance signal; determining effective left ventricular ejection time (ELVET) using check points within said cardiocycles; and discarding at least some of said cardiocycles which exhibit interference artifacts. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25)
-
16. The method of claim 13, further including determining cardiac output as a product of stroke volume and heart rate.
-
17. The method of claim 1, wherein suppressing breath waves further comprises:
-
calculating the Fourier transform of the bioimpedance signal; locating the first and second frequency harmonics of cardiocycles in the calculated spectrum of the signal; estimating the width of each of the harmonics; suppressing frequency harmonics below the lower bound of the second harmonic except for harmonics within the bounds of the first frequency harmonic; and calculating the inverted Fourier transform of the signal.
-
-
18. The method of claim 1, wherein an electrode array is employed for detecting said bioimpedance signals, and further comprising:
-
placing an upper influencing electrode on the patient'"'"'s head; placing a lower influencing electrode on the left lower extremity of the patient; placing an upper pair of detecting electrodes on the patient'"'"'s neck; and placing a lower pair of detecting electrodes on the trunk of the patient.
-
-
19. The method of claim 18, further comprising:
-
placing said upper influencing electrode on the patient'"'"'s forehead; placing said lower influencing electrode in the general area of the patient'"'"'s left knee; placing said pair of upper detecting electrodes on the patient'"'"'s neck; and placing said pair of lower detecting electrodes laterally on opposite sides of the patient'"'"'s chest.
-
-
20. The method of claim 19, wherein said upper influencing electrode comprises a spot electrode, and further comprising placing said upper influencing electrode substantially on an intersection of vertical and horizontal center lines of said patient'"'"'s forehead.
-
21. The method of claim 19, wherein said lower influencing electrode comprises a spot electrode, and further comprising placing said lower influencing electrode at a location which satisfies the relationship L<
- 5R, where L is the vertical distance between said upper and said lower influencing electrodes and R is the radius of said patient'"'"'s chest.
-
22. The method of claim 19, wherein said upper detecting electrodes comprises a pair of spot electrodes and said placement thereof is oriented symmetrically on opposite sides of said patient'"'"'s neck along a horizontal line approximately 4 centimeters above the base of said patient'"'"'s neck.
-
23. The method of claim 19, wherein said lower detecting electrodes further comprise a pair of electrode assemblies, each assembly providing contact surface area between about 12 and about 30 square centimeters, and further comprising orienting said assemblies laterally on opposite sides of said patient'"'"'s chest at approximately appendix level.
-
24. The method of claim 23, wherein each assembly further comprises four spot electrodes, wherein each spot electrode comprises approximately 4 square centimeters contact surface area with each said spot electrode centered at corners of a square with sides measuring 5 centimeters, and all 4 spot electrodes of said assembly electrically connected to each other.
-
25. The method of claim 24, further comprising placing the top spot electrodes of each assembly on the sword-shaped appendix level of the patient.
-
Specification