We consider the question of how the cardiac rhythm spontaneously self-regul
ates and propose a new mechanism as a possible answer. We model the neuroau
tonomic regulation of the heart rate as a stochastic feedback system and fi
nd that the model successfully accounts for key characteristics of cardiac
variability, including the 1/f power spectrum, the functional form and scal
ing of the distribution of variations of the interbeat intervals, and the c
orrelations in the Fourier phases which indicate nonlinear dynamics. (C) 19
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