The endogenous circadian pacemaker imparts a scale-invariant pattern of heart rate fluctuations across time scales spanning minutes to 24 hours

Kun Hu, Frank A.J.L. Scheer, Ruud M. Buijs, Steven A. Shea

Research output: Contribution to journalArticle

27 Scopus citations


Heartbeat fluctuations in mammals display a robust temporal structure characterized by scale-invariant/fractal patterns. These scale-invariant patterns likely confer physiological advantage because they change with cardiovascular disease and these changes are associated with reduced survival. Models of physical systems imply that to produce scale-invariant patterns, factors influencing the system at different time scales must be coupled via a network of feedback interactions. A similar cardiac control network is hypothesized to be responsible for the scale-invariant pattern in heartbeat dynamics, although the essential network components have not been determined. Here is shown that scale-invariant cardiac control occurs across time scales from minutes to ∼24 h, and that lesioning the mammalian circadian pacemaker (suprachiasmatic nucleus; SCN) completely abolishes the scale-invariant pattern at time scales >∼4 h. At time scales <∼4 h, the scale invariance persisted following SCN lesion but with a different pattern. These results indicate previously unrecognized multiscale influences of the SCN on heart rate fluctuations that cannot be explained by a simple pacemaker of 24-h rhythmicity. The conclusion is that the SCN serves as a major node in the cardiac control network and imparts scale-invariant cardiac control across a wide range of time scales with strongest effects between ∼4 and 24 h. These results demonstrate that experimental manipulations (e.g., SCN lesion) can be used to begin to model and understand the origin of scale-invariant behavior in a neurophysiological system.

Original languageEnglish (US)
Pages (from-to)265-273
Number of pages9
JournalJournal of biological rhythms
Issue number3
StatePublished - Jun 1 2008



  • Cardiac control
  • Feedback interactions
  • Network
  • SCN lesion
  • Scale-invariant patterns
  • The suprachiasmatic nucleus (SCN)

ASJC Scopus subject areas

  • Physiology
  • Physiology (medical)

Cite this