Mapping the cardiogenic impedance signal on the thoracic surface

The cardiogenic impedance signal from band electrodes placed in the traditional position around the neck and lower thorax was studied by mapping the location of the signal on the sternum using 10 cm strip electrodes in eight male subjects. The band current electrodes on the neck and waist were replaced with 10cm strip electrodes on the forehead and 10 cm below the xiphisternal joint, respectively, with only small changes in the dZ/dt peak amplitude and Z_o. Similarly, using a strip voltage pickup electrode at the level of the xiphisternal joint resulted in very small changes in the waveform. The amplitude of dZ/dt measured between the xiphisternal joint and points along the sternum remains small until approximately 10cm below the suprasternal notch, after which it increased linearly to the top of the neck. An average of 17 per cent and 24 per cent of the dZ/dt signal and 24 per cent and 22 per cent of the Z_o signal for supine and standing, respectively, occurs above the suprasternal notch. Replacing the current electrodes with strip electrodes on the forehead and waist caused only small changes in the signal. The position of the neck strip electrode is more critical.