A new ensemble averaging technique in impedance cardiography for estimation of stroke volume during treadmill exercise.

In this study, a new ensemble average technique is developed to measure cardiac output during treadmill exercise. Each dz/dt peak is used as a starting point for ensemble averaging, instead of the conventionally used R point of the ECG, in order to prevent the peak dz/dt waveform (C point) from smoothing, which results in increased dz/dtmax. The R-Z interval from the R point of the ECG to the peak dz/dt varies for each heart beat especially during strenuous exercise. Signal-to-noise ratios of five subjects obtained with the new technique are 0-32.6% higher than those obtained with the conventional technique at rest and during four levels of treadmill exercise. Power spectral densities of the averaged dz/dt waveforms by the peak dz/dt and R point references are also analyzed. Stroke volumes of the five subjects averaged by the peak dz/dt are 0-23.5% higher than those obtained by the R point at rest and during four levels of exercise.