Impedance Cardiography for Repeated Determination of Stroke Volume in Elderly Hypertensives: Correlation with Pulsed Doppler Echocardiography

In this double-blind, crossover study the authors have validated stroke volume determination by impedance cardiography against the pulsed Doppler echocardiographic method in elderly hypertensives. They found a good correlation between the stroke volume values obtained by the two methods over a range of values from 30 to 130 mL. The coefficient of linear regression was about .95 at each visit. The mean of the differences was -0.73 mL with a standard deviation of 8.46. Given that individual differences are normally distributed, the values corresponding to 2 standard deviations of the mean define a range covering 95% of the observed differences. From the distribution of the data around the mean plot it appears that, in comparison with pulsed Doppler, impedance cardiography tends to slightly underestimate stroke volumes of greater than 90 mL and to overestimate values of less than 50 mL. The results of this study indicate that impedance cardiography may represent a reliable alternative to pulsed Doppler echocardiography for the noninvasive estimation of cardiac output at rest in elderly patients.