Impedance cardiograms reliably estimate beat-by-beat changes of left ventricular stroke volume in humans.

Linear regression was used to compare stroke volumes calculated from tetrapolar impedance cardiograms and simultaneous left ventriculograms in 14 patients undergoing diagnostic left heart catheterisation. We calculated three to five consecutive stroke volumes from each ventriculogram. Left ventricular stroke volumes estimated by the two methods correlated closely: the correlation coefficients from pairs of data obtained from individual patients ranged between 0.77 and 1.00 (average = 0.91), and the correlation coefficient for pooled data (all pairs from all subjects) was 0.79 (p less than 0.001). Changes in left ventricular stroke volume measured with the two methods also correlated well (r = 0.89 for pooled data, p less than 0.001). The results suggest that impedance cardiograms provide reliable estimates of changes of beat-by-beat left ventricular stroke volumes and reasonable estimates of absolute levels of beat-by-beat stroke volumes in humans.