Mapping the cardiogenic impedance signal on the thorax

The cardiogenic electrical impedance signal was mapped on the anterior surface of the thorax. Using spot electrodes to pick up the impedance signal between the suprasternal notch and a point 10 cm below, stroke volume (SV) was measured with postural change and during 50-W bicycle exercise. The mapping showed that approximately 80% of the signal comes from the upper thorax. The impedance SV measured with spot electrodes showed poor agreement with results obtained with the dye dilution method during position change and exercise. The results suggest that the signal has multiple origins and that spot electrodes cannot simply be used to replace band electrodes without great care