Evidence for the origins and breakdown of 1/f noise in heart rate

We present the first systematic evidence for the origins and breakdown of 1/ f scaling in human heart rate. We confirm a previously posed conjecture that 1/ f scaling in heart rate is caused by the intricate balance between antagonistic activity of sympathetic (SNS) and parasympathetic (PNS) nervous systems. We demonstrate that modifying the relative importance of either of the two branches leads to a substantial decrease of 1/ f scaling. In particular, the relative PNS suppression both by congestive heart failure (CHF) and by the parasympathetic blocker atropine results in a substantial increase in the Hurst exponent H and a shift of the multifractal spectrum f (α) from 1/ f towards random walk scaling 1/ f 2 . Surprisingly, we observe a similar breakdown in the case of relative and neurogenic SNS suppression by primary autonomic failure (PAF). Further, we observe an intriguing interaction between multifractality of heart rate and absolute variability. While it is generally believed that lower absolute variability results in monofractal behaviour, as has been demonstrated both for CHF and the parasympathetic blockade, in PAF patients we observe conservation of multifractal properties at substantially reduced absolute variability to levels closer to CHF. This novel and intriguing result leads us to the conjecture that the multifractality of the heart rate can be traced back to the intrinsic dynamics of the parasympathetic nervous system.