The Development of Heart Rate Variability in Childhood-Insights into the Biology of Heart Rate Regulation

The current doctrine of dual regulation of Heart Rate Variability (HRV) via the autonomic nervous system has many limitations, mostly in children of different ages and nutritional states. Methods: We analyzed 24-hour HRV in a group of 126 healthy children with a normal Body Mass Index (BMI) in addition to 146 obese children with a BMI >90% and 32 children with anorexia nervosa with a BMI <10%. We included the ratio of body weight to body surface area in our analysis to prove the impact of thermogenesis on HRV analysis. Results: The high impact of age on HRV in the 126 healthy children with a normal BMI disappeared after including children with high and low BMIs. Linear regression analysis showed that HRV in childhood is not a sign of age-dependent maturation of the autonomic nervous system; rather, it is related to the age-dependent changes in body surface area, height, and weight. The ratio of body weight to body surface area indicates two different systems to regulate the heart rate in children with a ratio >/<30 kg/m2. Conclusion: Our data indicate a third regulatory system that is important in HRV analysis in addition to the dual regulation of the vagus and sympathicus. This system is related to age-dependent changes in body surface area, height, and weight. These factors depend on nutrition and energy demands and are probably regulated by the HCN4 gene.