抄録
A computer-based system for calculating stroke volume, heart rate and cardiac output automatically from the transthoracic impedance variation has been developed. A beat-by-beat determination has been performed on several healthy subjects and a patient with atrial fibrillation either during breath holding maneuver or during spontaneous breathing at rest. A mini-computer was used to measure the systolic peak height of the first derivative of impedance change (dZ/dt) min, the ventricular ejection time ET and the basic impedance of the thorax Z0 for each cardiac cycle. The ET was determined on the dZ/dt wave from the time point corresponding to.15 (dZ/dt) min, to the most positive peak following systole. The respiratory drift appearing on the dZ/dt during breathing was corrected by determining the base line for each cardiac cycle, using as reference the dZ/dt values at ECG-R wave which was obtained during breath holding maneuver. Stroke volume was, then calculated using the formula of Kubicek et al. (1966). Heart rate was determined from R-R interval of ECG. Cardiac minute volume was obtained by multiplying the heart rate by stroke volume. A comparison between the computed stroke volumes and those obtained from a manual calculation showed good agreement.
