Impedance cardiography using band and regional electrodes in supine, sitting, and during exercise

The electrical impedance and its first derivative (dZ/dt) were measured at 100 kHz on 10 normal males in supine, sitting, and during upright bicycle exercise in order to compare the contribution of regional electrodes to the standard band electrode signal and to evaluate the possible use of spot electrodes for stroke volume (SV) measurements. Simultaneous measurements were made from band electrodes placed around the neck and lower thorax and from spot electrodes which recorded signals from the neck, upper thorax, and lower thorax. The results showed that approximately equal parts of the dZ/dt waveform came from the neck and upper thorax with the lower thorax contribution small but providing important features of the band signal. Changing from supine to sitting showed percentage decreases of 35% and 46% for the band and neck signals, respectively, with an increase of 19% for the upper thorax signal. The percentage increases in SV with upright exercise were 34%, 52%, and 24% for the bands, neck, and upper thorax signals, respectively. Band signal is made up of different signals from various regions of the thorax. Its ability to predict correct changes in SV may result from some "lucky" coincidences. The use of regional electrodes will probably not give the same SV information but may be important in measuring regional activities of the central circulation.