Impedance cardiography for determination of stroke index.

Stroke index obtained by impedance cardiography was compared with values obtained by dye-dilution technique in 17 subjects in 122 determinations made within 2 min of each other. Fifty of these determinations were done after drug administration, postural change, or saline infusion. All values obtained by both methods correlated significantly, but with wide scatter (r=0.49, n = 122, P less than 0.001). The series of determinations within each subject, however, correlated only in one subject significantly; thus any changes of stroke index measured by both techniques were not commensurate. In addition, the impedance stroke index values were significantly lower than the dye-dilution technique, impedance cardiography presently does not determine reliably absolute values of stroke index and is not suitable to evaluate changes of stroke index.