Nonstationarity and 1/f noise characteristics in heart rate

Presents several methods for estimating the exponent /spl alpha/ of the 1/f/sup /spl alpha//-type spectral behaviour of heart rate (HR) power spectrum. The authors give a comparison of the statistical properties of various estimators, i.e., maximum likelihood estimation (MLE), Hurst exponent, detrended fluctuation analysis (DFA) and regression of the power spectrum. A method to investigate nonstationarity is explained and applications of these estimators to long term HR recordings are given. The results obtained indicate that the power-law structure of HR is nonstationary and that observed 1/f/sup /spl alpha// patterns may be due to the interaction of the estimators with the nonstationarity in the exponent /spl alpha/.