The most widely used equation, V = pL2/R, is developed for the computation of ventricular volume from catheter based impedance measurements. The assumptions implicit in this derivation are examined and found to be generally invalid. An empirical discrete resistor model is described which includes the impedance of the myocardial tissue and the adjoining ventricular blood volume. Once the parameters...

Stroke volume measurements made by a catheter-based, right ventricular, intracardiac impedance system at rest and during upright bicycle ergometry were found to compare favorably with measurements made by acetylene rebreathing (r = 0.96, n = 13) and by radionuclide ventriculography (r = 0.96, n = 13) in a 46-year-old male pacemaker-dependent subject. The impedance information was then used to control the ventricular pacing rate during bicycle exercise, utilizing an algorithm that attempts to maintain a constant stroke volume. This resulted in a 23% increase in cardiac output accompanied by a 70% decrease in stroke volume as compared to the values measured during the same exercise at 70 pulses per minute (ppm).