Monofractality in RR Heart Rate by Multifractal Tools

Multifractal formalism is tested if it can work as a robust estimator of monofractals when scaling intervals are fixed. Intervals for scaling are selected to be consistent with known frequency bands of power spectral analysis used in estimates of heart rate variability: low frequency (LF), very low frequency (VLF), and ultra low frequency (ULF). Tests on fractional Brownian motions and a binomial cascade are performed to validate popular multifractal methods: Wavelet Transform Modulus Maxima and Multifractal Detrended Fluctuation Analysis. Then the methods are applied to identify monofractal elements of control processes driving the heart rate. A transition is found in the dynamic organization of autonomic nervous system control of the heart rate related to the change in scaling intervals. The control over the diurnal heart rate is of a multifractal type when considered in LF and of a monofractal type when observed in ULF. Additionally, this transition affects on a switch in a relation between widths of diurnal and nocturnal multifractal spectra. (author)