Ventricular volume curves obtained from thoracic impedance measurements

An electrode arrangement for impedance measurements has been developed, which results in a waveform that appears to represent ventricular volume. The waveform shows an increasing systolic impedance change and has the general shape of a ventricular volume curve. The surface electrode arrangement has been evaluated on six subjects in the supine, sitting position and during bicycle exercise at 50 W. An impedance measurement using an electrode arrangement similar to that used in conventional impedance cardiography was also recorded along with an arterial pressure waveform. The change in the slope of the ventricular filling curve with positional change and exercise was as would be expected based on physiology. The start of the ventricular signal was delayed from what would be expected based on the arterial pressure pulse, whereas the conventional impedance waveform started before the pressure purse. More research is needed to evaluate the measurements as estimations of stroke volume or other cardiac performance parameters