Fractal properties of human muscle sympathetic nerve activity

Paul J. Fadel, Hakan S. Orer, Susan M. Barman, Wanpen Vongpatanasin, Ronald G. Victor, Gerard L. Gebber

Research output: Contribution to journalArticle

14 Scopus citations

Abstract

Muscle sympathetic nerve activity (MSNA) in resting humans is characterized by cardiac-related bursts of variable amplitude that occur sporadically or in clusters. The present study was designed to characterize the fluctuations in the number of MSNA bursts, interburst interval, and burst amplitude recorded from the peroneal nerve of 15 awake, healthy human subjects. For this purpose, we used the Allan and Fano factor analysis and dispersional analysis to test whether the fluctuations were time-scale invariant (i.e., fractal) or random in occurrence. Specifically, we measured the slopes of the power laws in the Allan factor, Fano factor, and dispersional analysis curves. In addition, the Hurst exponent was calculated from the slope of the power law in the Allan factor curve. Whether the original time series contained fractal fluctuations was decided on the basis of a comparison of the values of these parameters with those for surrogate data blocks. The results can be summarized as follows. Fluctuations in the number of MSNA bursts and interburst interval were fractal in each of the subjects, and fluctuations in burst amplitude were fractal in four of the subjects. We also found that fluctuations in the number of heartbeats and heart period (R-R interval) were fractal in each of the subjects. These results demonstrate for the first time that apparently random fluctuations in human MSNA are, in fact, dictated by a time-scale-invariant process that imparts "long-term memory" to the sequence of cardiac-related bursts. Whether sympathetic outflow to the heart also is fractal and contributes to the fractal component of heart rate variability remains an open question.

Original languageEnglish (US)
Pages (from-to)H1076-H1087
JournalAmerican Journal of Physiology - Heart and Circulatory Physiology
Volume286
Issue number3 55-3
StatePublished - Mar 1 2004

Keywords

  • Allan factor
  • Dispersional analysis
  • Fano factor
  • Heart rate variability
  • Long-range correlations
  • Time-scale invariance

ASJC Scopus subject areas

  • Physiology
  • Cardiology and Cardiovascular Medicine
  • Physiology (medical)

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    Fadel, P. J., Orer, H. S., Barman, S. M., Vongpatanasin, W., Victor, R. G., & Gebber, G. L. (2004). Fractal properties of human muscle sympathetic nerve activity. American Journal of Physiology - Heart and Circulatory Physiology, 286(3 55-3), H1076-H1087.