A model for the cardiac-associated changes of the thoracic electrical impedance in man.

A simple mathematical model has been developed which is able to fit the impedance waveform produced by normal and abnormal subjects throughout the cardiac cycle with reasonable precision. Contributions from both the aorta and vena cava are significant. Fitted values of model parameters offer potentially useful clinical information. Estimates of the stroke volume obtained from the model correlate will with values derived from the maximum rate of change of the thoracic impedance during systole, but are in poorer agreement with values obtained using tracer dilution techniques.