Analysis of correlations in heart dynamics in wake and sleep phases

We study correlations in time series of RR intervals of subjects with normal sinus rhythm (NSR) during sleep and wake phases and we also analyze time series of subjects with congestive heart failure (CHF) in both phases. We use detrended fluctuation analysis (DFA), the Higuchi's method and multifractal analysis. We have obtained different results for sleep and wake phases. The time series of healthy subjects show long-range correlations during sleep and wake conditions; on the other hand, for CHF subjects we have found different correlations during sleep and wake phases. This is confirmed by using both DFA and Higuchi's methods. We have found that the width of the multifractal spectra is practically the same for both phases of healthy subjects and CHF subjects. However, when we study with detail the spectra we observe that the spectra of unhealthy persons are almost symmetrical whereas the spectra of healthy subjects are asymmetrical.