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

Abstract

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.

Comparability of Spot Versus Band Electrodes for Impedance Cardiography

“…The third investigation of spot-band comparability was conducted by Patterson, Wang, and Raza (1991). Patterson and colleagues measured Z 0 , dZ/dt peak , and SV during a supine resting condition, a sitting condition, and physical exercise.…”

“…The authors also evaluated different combinations of spot-band locations and concluded that the dZ/dt waveforms significantly differed among any pairing of spot and/or band combinations. Patterson et al (1991) concluded that placement of electrodes at varying locations resulted in substantial differences in estimates of Z 0 , dZ/dt, and SV.…”

“…The order of electrode placements was counterbalanced, and an approximate 30 min period separated the two assessment sessions. Electrode data were input Like Boomsma et al (1989) and Patterson et al (1991), Sherwood and colleagues (1992) found the mean Z 0 for spot electrodes was significantly lower than the mean Z 0 for band electrodes. However, Sherwood and colleagues found the mean SV for spot electrodes was significantly lower than the mean SV for band electrodes.…”

“…The authors also evaluated different combinations of spot-band locations and concluded that the dZ/dt waveforms significantly differed among any pairing of spot and/or band combinations. Patterson et al (1991) concluded that placement of electrodes at varying locations resulted in substantial differences in estimates of Z 0 , dZ/dt, and SV.The Patterson et al (1991) study is important because it demonstrated that the location of the electrode as well as the type of electrode influenced measurement of cardiac functioning using impedance cardiography. Consequently, spot-band investigations that placed the two sets of electrodes at different levels along the thorax would be confounding electrode location with electrode type.…”

“…For example, it might have been possible that the differences in level of CO would have been observed if the participants were run through the protocol twice using bands on both occasions. A second limitation is that the spot and band electrodes were placed at different levels on the thorax, which, as noted by Patterson et al (1991), can lead to differences in impedance values even when similar electrodes are used.The fifth and final investigation of spot-band comparability, conducted by Gotshall and Sexson (1994), assessed participants in both a supine and standing position. Impedance measures of Z 0 , SV, dZ/dt, and LVET were collected using two spot voltage electrodes placed on either side of the base of the neck on the midaxillary line and two spot voltage electrodes placed on either side of the thorax on the midaxillary line at the level of the xiphisternal junction.…”