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

Abstract

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 >90 mL and to overestimate values of <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.