Apparatus and method for measuring cardiac output

Claim 1

A method of measuring cardiac output of a patient, the method comprising the steps of: a) measuring electrical impedance between two locations on the patient, for a predetermined first time interval, thereby obtaining an impedance signal over said first time interval, b) differentiating said impedance signal to obtain a signal representative of a first derivative of said impedance signal over said first time interval, c) computing a frequency transform of said first derivative of said impedance signal, for each of a plurality of discrete second time intervals, each second time interval being at least an order of magnitude shorter than said first time interval, each of said frequency transforms comprising a function of power versus frequency at one of said second time intervals, d) computing a plurality of,definite integrals of each of said frequency transforms, the definite integrals being taken over a predetermined range of frequencies, e) assembling a graph having an abscissa which comprises time, and an ordinate comprising one of said definite integrals which corresponds to a time represented by the abscissa, f) identifying points in time at which extrema appear in the graph produced in step (e), and determining corresponding points in time in said first derivative of said impedance signal, g) using said points in the first derivative of said impedance signal to determine a maximum excursion of said first derivative of said impedance signal and to determine a time interval corresponding to ventricular ejection time of the patient, and h) calculating cardiac output according to the maximum first derivative of said impedance signal and the ventricular ejection time determined in step (g).

Claim 2

A method of measuring cardiac output of a patient, the method comprising the steps of: a) measuring electrical impedance between two locations on the patient, for a predetermined first time interval, thereby obtaining an impedance signal over said first time interval, b) differentiating said impedance signal to obtain a signal representative of a first derivative of said impedance signal over said first time interval, c) computing a frequency transform of said first derivative of said impedance signal, for each of a plurality of discrete second time intervals, each second time interval being at least an order of magnitude shorter than said first time interval, each of said frequency transforms comprising a function of power versus frequency at one of said second time intervals, d) computing a plurality of,definite integrals of each of said frequency transforms, the definite integrals being taken over a predetermined range of frequencies, e) assembling a graph having an abscissa which comprises time, and an ordinate comprising one of said definite integrals which corresponds to a time represented by the abscissa, f) identifying points in time at which extrema appear in the graph produced in step (e), and determining corresponding points in time in said first derivative of said impedance signal, g) using said points in the first derivative of said impedance signal to determine a maximum excursion of said first derivative of said impedance signal and to determine a time interval corresponding to ventricular ejection time of the patient, and h) calculating cardiac output according to the maximum first derivative of said impedance signal and the ventricular ejection time determined in step (g).

Claim 5

A method of measuring cardiac output, the method comprising the steps of: a) obtaining a signal corresponding to a first derivative of electrical impedance of a patient, with respect to time, b) deriving, for each moment in time, a function which relates intensity of the signal to its frequency, and deriving a graph corresponding to said function, c) computing a definite integral of each graph derived in step (b), over a frequency range of interest, and plotting said computed definite integrals as a function of time to form another graph, d) comparing extrema of the graph formed in step (c) with the signal obtained in step (a) to identify points on the signal of step (a) which determine a maximum impedance derivative and a ventricular ejection time, and e) computing cardiac output from knowledge of the maximum impedance derivative and the ventricular ejection time

Claim 6

A method of measuring cardiac output, the method comprising the steps of: a) obtaining a signal corresponding to a first derivative of electrical impedance of a patient, with respect to time, b) deriving, for each moment in time, a function which relates intensity of the signal to its frequency, and deriving a graph corresponding to said function, c) computing a definite integral of each graph derived in step (b), over a frequency range of interest, and plotting said computed definite integrals as a function of time to form another graph, d) comparing extrema of the graph formed in step (c) with the signal obtained in step (a) to identify points on the signal of step (a) which determine a maximum impedance derivative and a ventricular ejection time, and e) computing cardiac output from knowledge of the maximum impedance derivative and the ventricular ejection time

Claim 9

A method of measuring cardiac output of a patient, the method comprising the steps of: a) measuring electrical impedance of the patient's body, and computing a first graph of said impedance as a function of time, b) computing a plurality of definite integrals of a transform of a signal represented in said first graph, over a frequency range of interest, and deriving a second graph by plotting said definite integrals as a function of time, and c) comparing said first graph with said second graph, said second graph having a recognizable pattern of extrema, wherein the extrema of the second graph identify points on the first graph which determine parameters from which one can calculate cardiac output, and using said parameters to calculate cardiac output.

Claim 10

A method of measuring cardiac output of a patient, the method comprising the steps of: a) measuring electrical impedance of the patient's body, and computing a first graph of said impedance as a function of time, b) computing a plurality of definite integrals of a transform of a signal represented in said first graph, over a frequency range of interest, and deriving a second graph by plotting said definite integrals as a function of time, and c) comparing said first graph with said second graph, said second graph having a recognizable pattern of extrema, wherein the extrema of the second graph identify points on the first graph which determine parameters from which one can calculate cardiac output, and using said parameters to calculate cardiac output.