Patent ID: 7740590

Claim:
An apparatus for determining stroke volume by bioimpedance from a patient, comprising: two or more spaced apart alternating current flow electrodes positionable on a patient; two or more spaced apart voltage sensing electrodes positionable on the patient and between the alternating current flow electrodes; an alternating current source electrically connected to the alternating current flow electrodes; a voltmeter electrically connected to the voltage sensing electrodes; and a processing unit in communication with the voltage sensing electrodes, wherein the processing unit is configured to use a voltage sensed by the voltage sensing electrodes to calculate a cardiogenically induced impedance variation value of the patient, and to determine a stroke volume of the patient by multiplying the cardiogenically induced impedance variation value by a volume conductor V C and by a left ventricular ejection time T LVE ; wherein the processing unit determines the volume conductor V C as: V C = ( C 1 - C 1 ⁢ Z 0 Z c + Z 0 2 Z c 2 ) · ( C 2 · W · C 3 ) , where: C 1 is at least 1.0 and no greater than 8.0, Z 0 is a transthoracic base impedance or a static D.C. component of a total transthoracic impedance, Z c is a critical level of base impedance that is at least 15Ω and no greater than 25Ω, C 2 is at least 0.10 and no greater than 0.75, W is a kilogram weight of the patient, and C 3 is at least 35 and no greater than 100.