Computer method of predicting the reliability of impedance cardiography stroke volume measurements

Impedance cardiography (ICG) is a novel noninvasive technique for measuring stroke volume (SV) on the basis of impedance changes in the thorax to applied electrical alternating current. ICG has not been broadly accepted for clinical use mainly because the most widely used formulas for SV by Kubicek and Sramek fail to reliably determine absolute values of SV for a large subset of patients. In 36 patients, SV was obtained by ICG using the Sramek equation and simultaneously by aortic Doppler combined with 2D-echo aortic root measurement. The ICG dZ/dt wave during ventricular ejection (C-wave) was compared to a triangular template which represented a model of a "normal" C-wave for a healthy adult. The Sramek equation provided the most reasonable estimates of SV when the C-wave fitted the triangular template, which did not appear to correspond with any subset of patients. This suggests that solely using the height of the C-wave, [dZ/dt]/sub max/, may be responsible for the unreliability of the Sramek and possibly Kubicek equations for SV determination.