Characterization of heart rate dynamics in infants as a probe for neural state and age

Heart rate variation is a powerful tool for investigating the state of the central nervous system (CNS). Changes in this variation can be studied in infants over developmental periods to examine maturation of the CNS. This work examines these changes using several methods in order to characterize changes in heart rate patterns across conceptional ages and sleep-wake states. The authors´ methods included comparison of mean heart rates across EEG-sleep states, quantitative analysis of Poincare plots, and examination of R-R interval frequency changes over time. The authors´ results show that mean heart rate is highly dependent on state, even in very premature infants, and that R-R interval frequency becomes more indicative of state after 35 weeks conceptional age (CA). Also, an increase in heart rate variability over age for all sleep waking states was noted with higher frequency components of R-R interval changes during quiet sleep states. Larger frequency changes were apparent over progressively maturing ages for quiet sleep when compared to active sleep. These findings most likely reflect maturation of heart rate modulation by the CNS, with variations across states possibly indicating differences in developmental patterns of the sympathetic and parasympathetic branches of the autonomic nervous system