On the fractal nature of heart rate variability in humans: effects of vagal blockade

Am J Physiol. 1995 Oct;269(4 Pt 2):R830-7. doi: 10.1152/ajpregu.1995.269.4.R830.


The purpose of the present study was to investigate the effects of the vagal blocker atropine on the fractal nature of human heart rate variability (HRV) at rest. Approximately 10-min segments of beat-to-beat heartbeat intervals, i.e., HRV, of 10 normal subjects and 11 cardiac disease patients were measured before and after intravenous injection of 0.5-0.75 mg atropine sulfate. HRV data were analyzed by coarse graining spectral analysis (Y. Yamamoto and R. L. Hughson, Physica 68D: 250-264, 1993) to break down their total power into harmonic and nonharmonic (fractal) components. The harmonic component was used to calculate the contribution of high (> 0.15 Hz)-frequency components to total HRV power (%HF). From the fractal component, the contribution of the fractal component to total HRV power (%fractal), the spectral exponent beta, and Hurst scaling exponent (H) were calculated. For both normal subjects and cardiac patients, atropine resulted in significantly (P < 0.05) less mean HRV and significantly (P < 0.05) greater beta compared with control, whereas mean values for %fractal were as high as 70% and were not significantly (P > 0.05) different between atropine and control. The mean value of H with atropine was significantly (P < 0.05) greater than that for control. Directional changes in %HF and beta were consistent with only one exception for a patient who had the smallest change in log %HF by atropine. The normally irregular fractal pattern of resting HRV was decreased by atropine as shown by the decrease in %HF and the increase in beta.(ABSTRACT TRUNCATED AT 250 WORDS)

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Aged
  • Atropine / pharmacology
  • Female
  • Fractals*
  • Heart Diseases / physiopathology
  • Heart Rate* / drug effects
  • Humans
  • Male
  • Middle Aged
  • Nerve Block
  • Parasympatholytics / pharmacology
  • Reference Values
  • Vagus Nerve / physiology*


  • Parasympatholytics
  • Atropine