Measurement of stroke volume with impedance cardiography

Simultaneous determination of stroke volume with impedance cardiography and the dye dilution technique was compared in 11 healthy men before and after exercise. The correlation coefficient for all measurements was 0.82. Mean stroke volume determined by impedance cardiography was significantly (P less than 0.001) lower than mean stroke volume calculated by the dye dilution technique. However, there was no significant difference in the mean change in stroke volume determined by the two techniques during serial measurements. The reproducibility of single impedance-determined stroke volumes (6.9 ml) was not significantly different from single values obtained by dye dilution (7.3 ml). Impedance cardiography was found to be a safe, reliable, non-invasive method for the measurement of changes in stroke volume in healthy individuals before and after exercise. At present, direct estimation of absolute values of stroke volume is not recommended using impedance cardiography. Calibration of the impedance technique against other established techniques in a given application is necessary.