The chaotic component of human heart rate variability shows a circadian periodicity as documented by the correlation dimension of the time-qualified sinusal R-R intervals.

OBJECTIVE

This study investigates the hypothesis that the nonlinear component of human heart rate (HR) variability might show a periodic structure over the 24-h span. Such a postulate could explain how the chaotic component might coexist with the deterministic periodic variability of instantaneous HR in beat per minute.

MATERIALS AND METHODS

The sinusal R-R intervals (sRRi) of the Holter EKG of 10 clinically healthy subjects (5 M, 5 F, 23-30 years) were analyzed per each hour of the day-night span according to two methods for the nonlinear chaotic variability, i.e., the correlation dimension method, and the linear periodic variability, i.e., periodic regression analysis.

RESULTS

The hourly-qualified correlation integrals were found to show a significant circadian rhythm, with an acrophase located during the night in coincidence with the longest duration of the sRRi and the lowest rate of cardiac pulse.

CONCLUSIONS

The rhythmic structure of the chaotic component of the human HR variability let us to think that a deterministic periodic chaos of fractal type regulates the nonlinear cardiac dynamics. Such a periodic structure allows the chaos to be compatible with the deterministic linear periodicity of circadian type which characterizes the within-day variability of human HR.