Stationarity of the heart rate variability by acceleration plethysmography: short-term measurements of healthy young males in daily life.

The acceleration plethysmography (APG) is a useful tool to analyze the heart rate variability (HRV) with the merits of being portable and simple in operation. To use it clinically, 'stationarity' of the HRV measurements in resting state should be justified as a fundamental premise. Therefore, the purpose of this research was to investigate the stationarity of the short-term HRV derived from APG in resting state in daily life. The sample size was determined on the basis of alpha = 0.05 and beta = 0.20. The HRV measurements of 44 healthy male subjects were done twice during a one-week period by the APG system. The HRV parameters were examined by the assessments of distribution, equality of the mean and variance and internal consistency reliability. Concerning spectral components represented as proportion, normalized units and the logarithm of the rate of each component, the normal distribution and the homogeneity of variance in two measurements were confirmed. Significant difference was not found between the mean values in two measurements. The internal consistency reliability evaluated by Cronbach's alpha of 0.6-0.7 was acceptable for every parameter. It is concluded that for healthy young males, the parameters of short-term HRV derived from APG measured in resting state in the same time zone in daily life remain stationary within a certain range regardless of the measurement day.