From 1/f noise to multifractal cascades in heartbeat dynamics

We explore the degree to which concepts developed in statistical physics ca n be usefully applied to physiological signals. We illustrate the problems related to physiologic signal analysis with representative examples of huma n heartbeat dynamics under healthy and pathologic conditions. We first revi ew recent progress based on two analysis methods, power spectrum and detren ded fluctuation analysis, used to quantify long-range power-law correlation s in noisy heartbeat fluctuations. The finding of power-law correlations in dicates presence of scale-invariant, fractal structures in the human heartb eat. These fractal structures are represented by self-affine cascades of be at-to-beat fluctuations revealed by wavelet decomposition at different time scales. We then describe very recent work that quantifies multifractal fea tures in these cascades, and the discovery that the multifractal structure of healthy dynamics is lost with congestive heart failure. The analytic too ls we discuss may be used on a wide range of physiologic signals. (C) 2001 American Institute of Physics.