An improved approach for measurement of stroke volume during treadmill exercise

In this study, a new ensemble averaging technique was 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 ECG, in order to prevent the peak dz/dt waveform (C point) to be smoothed, which results in increased dz/dt_max. When using the R point as a reference, time interval from the R point to the peak dz/dt varies for each heart beat. Signal to noise ratios (SNR) of the five subjects with the new technique were 12.9, 16. 4, 10.6, 14.0, and 4.6% higher than those with the conventional one at rest and during four levels of exercise, respectively. Power density spectra of the averaged dz/dt waveforms by the peak dz/dt and R point referencing were also analyzed. Stroke volumes of the five subjects averaged by the peak dz/dt were 4.9, 6.8, 7.6, 7.4, and 9.8% higher than those by the R point at rest and during four levels of exercise, respectively.