the invention provides apparatus and methods for using the electrical bioimpedance measurements to monitor parameters associated with blood flow in a segment of body tissue . the invention eliminates the effect of respiration from the thoracic impedance as a function of time to provide a signal indicative of pulsatile thoracic impedance changes continuously . the pulsatile thoracic impedance signal is processed to produce signals indicative of the ventricular ejection time and the maximum rate of change of pulsatile thoracic impedance which are used in a microprocessor to calculate the volume of blood pumped per stroke according to an improved systolic upstroke equation .