Multifractal analysis of heart rate variability

We have studied the R-R variability of five young and five elderly subjects for multi-fractal behaviour using a partition function method. The partition function, obtained using the wavelet transform modulus maxima method, allowed the computation of local Hurst exponents. The multi-fractal spectrum was obtained from the Hurst exponents using a Legendre transformation. The computations revealed specific values of the Hurst exponent at which the multi-fractal spectrum peaked, with a clear separation between young and elderly subjects. The peaks of the young subjects occurred for Hurst exponents in the range 0.06 to 0.13, whereas the peaks for the elderly subjects were in the range 0.29 to 0.36