Nonstationarity and 1/f noise characteristics in heart rate

This paper presents several methods for estimating the exponent alpha of the 1/f(alpha)-type spectral behaviour of heart rate (HR) power spectrum. We 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 longterm HR recordings are given. The results obtained indicate that the power-law structure of HR is nonstationary and that observed 1/f(alpha) patterns may be due to the interaction of the estimators with the nonstationarity in the exponent alpha.