Abstract
Electrical impedance (or admittance) cardiography is a simple and still potential method for non-invasive and continuous monitoring of stroke volume and cardiac output (CO) by detecting the electrical impedance of a thorax which is roughly assumed to be a two-compartment coaxial cylindrical model composed of the aorta and its surrounding thoracic tissues. Although the band-electrode method proposed by Kubicek et al. has been widely used for the detection of the electrical impedance, long-term use of the band-electrodes is often uncomfortable and causes inflammation of the skin. Replacement of band-electrodes with spot-electrodes is therefore highly required for clinical practice. We have previously investigated an optimal spot-electrodes array from such a view point, and reported these results in this journal. However, the current distribution during cardiac blood ejection period showed little uniformity, and detailed investigation of this phenomenon was remained as a future problem. The present study concerns with this problem through the analysis of pulsatile components of the thoracic impedance along the medial line of the thorax by a finite element method and those by actual measurement. From these investigations, an optimal electrodes-location for voltage pick-up was to be determined as the medial portion at the level of the clavicle and the portion above the xiphisternum. Furthermore, we have investigated the accuracy of CO measurement using impedance cardiography by the new spot-electrode array to that using a pulse dye-densitometry method. From the CO comparison experiments, bias and precision calculated for the impedance cardiography versus a pulse dye-densitometry method averaged -0.43±1.42 L/min, the validity and reasonable accuracy of the new spot-electrodes array was clearly demonstrated.
