Part 6: Multifractality of healthy human heart rate
Multifractality has been uncovered in a number of fundamental physical and chemical processes (9). Recently, it was also reported that heart rate fluctuations of healthy individuals are multifractal (11). This finding posed new challenges to our understanding of heart rate regulation as most modeling of heart rate fluctuations over long time scales had concerned itself only with monofractal properties (12). For example, it appears that a major life-threatening condition, congestive heart failure, leads to a loss of multifractality (Fig. 8).
|More importantly, neither monofractal nor multifractal
behaviors are accounted
for by current understanding of physiological regulation based on homeostasis.
Hence it would be beneficial, perhaps, to uncover how
multifractality in the
healthy heart dynamics arises. Two distinct possibilities can be considered.
The first is that the observed multifractality is primarily a consequence
of the response of neuroautonomic control mechanisms to activity-related
fractal stimuli. If this were the case, then in the absence of such correlated
inputs the heartbeat dynamics would not generate such a heterogeneous
multifractal output. The second is that the neuroautonomic control mechanisms---in the presence of even weak external noise---endogenously generate