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Recent studies outlined linear and non-linear dynamics in heart rate variability; however, their physiological origin is still unknown. The present study investigated the impact of cerebral function on linear and non-linear dynamics in heart rate variability. Electrocardiograms from seven brain dead organ donors and seven healthy volunteers were analyzed. Atropine was used in healthy volunteers to adjust their heart rate to that of the donors. As compared to healthy volunteers without atropine, the linear dynamics of heart rate variability, determined by time and frequency domain analyses, were significantly reduced in healthy volunteers with atropine and, to an even greater extent, in donors. Atropine tended to increase the complexity and non-linearity of heart rate variability in healthy volunteers, as determined by the correlation dimension D and the largest Lyapunov exponent L, respectively (D = 9.43 +/- 2.93 vs. 7.65 +/- 0.97 and L = 0.525 +/- 0.099 vs. 0.504 +/- 0.047 bits.beat-1; both NS), while these indices were significantly reduced in donors by 19.5 +/- 12.8% and 15.0 +/- 11.7%, respectively (D = 6.16 +/- 0.98 and L = 0.428 +/- 0.059 bits.beat-1; both p0.05 vs. volunteers). Thus, loss of cerebral function reduces both linear and non-linear components of heart rate variability.

We studied the relation between central-autonomic adaptability (largest Lyapunov exponent of heart rate dynamics) and visual learning capability (total net score in Kimura's Recurring-Figures-Test) in 15 healthy subjects and 35 patients with cerebral white matter diseases (12 with optic neuritis and 23 with multiple sclerosis), aged between 18 and 39 years. In optic neuritis patients and in those with very early, clinically asymptomatic multiple sclerosis, we found high correlations between these central-autonomic and cognitive functions (r =.66 and r =. 86, respectively, p

In a study of central autonomic dynamics in early multiple sclerosis, we measured the temporal oscillations of the momentary heart rate (heart rate dynamics). 11 young patients suffering from relapsing remitting definite multiple sclerosis in relapse-free and early stages of illness and 11 healthy controls were examined under vagotonic and sympathicotonic conditions. The temporal structure of the heart rate dynamics was operationalized phase-space analytically through the estimation of the largest Lyapunov exponent. Positive Lyapunov exponents were found in all participants under all conditions indicating deterministically chaotic heart rate oscillations. The variance analysis of these exponents detected no significant effect of sympathetic or vagal activity (experimental condition) but a significant group difference (p.02). The multiple sclerosis patients were characterized by significantly lower Lyapunov exponents than the healthy controls. This finding suggests a more stable and thus less adaptive central-autonomic organization in early multiple sclerosis.

In a study of central autonomic organization in interictal states of idiopathic generalized epilepsy, we measured the spontaneous oscillations of the heart rate in 8 young epileptics with normal interictal electroencaphalograms (EEGs), 6 young epileptics with epileptiform discharges in the interictal EEGs and 8 healthy controls. The temporal structure of the heart rate (HR) dynamics was operationalized through the estimation of the largest Lyapunov exponent (LLE). For all patients and controls, the LLEs of the HR dynamics were positive, indicating chaotic oscillations. The patients with interictal epileptiform discharges showed significantly lower LLEs of the HR dynamics than the epileptics with normal EEGs and the healthy controls. By comparison, the values of the epileptics with normal EEGs und those of the healthy controls did not differ significantly. This finding suggests a more rigid and thus less adaptable central cardio-autonomic organization in epileptics with epileptiform discharges in the interictal EEG.