Fundamentals of impedance cardiography.

The most widely used impedance method for cardiac stroke volume and cardiac output measurements is described. It uses band electrodes around the ends of the thorax and forward extrapolation of the systolic portion of the impedance waveform. Studies performed to determine the physiological origin of the impedance change and the apparently conflicting results are summarized. Comparative studies with other methods are briefly discussed. It is concluded that for the present technique to be placed on a sound scientific base, it is necessary to determine what regions or organs contribute to the impedance change recorded from the thoracic surface, but that it shows remarkably good correlation with other cardiac output measurement systems if applied to a select relatively healthy population, given all the assumptions involved.