The influence of sleep state (i.e., active and quiet) on heart period, heart period variability, respiratory sinus arrhythmia (RSA), and the coupling between RSA and heart period was evaluated in 24 healthy full-term newborns. Electrocardiogram (ECG) data were collected, and sleep state was coded 1 hr after feeding until at least 10 min of data were collected in states of active and quiet sleep. ECG data were analyzed for the first five continuous minutes of each sleep state. Relative to active sleep, quiet sleep was associated with significantly higher amplitude RSA, lower heart period variability, and longer heart periods. Because RSA amplitude reflects the functional output of vagal pathways originating in the nucleus ambiguus, it was hypothesized that sleep state would influence how these vagal pathways regulate instantaneous changes in heart period. A new method, evaluating the instantaneous coupling of RSA and heart period, demonstrated that coupling was significantly greater during active sleep. The neurophysiological explanation extends the polyvagal theory to include potential cortical-brain stem connections.

Twenty very low birth weight (VLBW) children participated in a longitudinal follow-up study designed to explore the relation between neonatal physiological measures and school-age (6-9 years) outcome measures. Neonatal measures of mean heart period and cardiac vagal tone (respiratory sinus arrhythmia, RSA) were derived from weekly recordings at 33, 34, and 35 weeks gestational age. An RSA Maturation measure was calculated across the 3-week period to assess functional changes in vagal regulation of the heart during a period in which there is enhanced myelination of the vagus. In addition, the relation of neonatal risk measures (low birth weight, low socioeconomic status, high medical risk) and preschool measures (behavior, cognitive abilities) to school-age outcome measures was examined. As expected, school-age measures were closely related to preschool measures within the same domain. Neonatal risk measures were not related to school-age outcome measures. Of the neonatal physiological measures, RSA maturation was correlated with a single school-age measure, social competence as measured by the Child Behavior Checklist (Achenbach, 1988). Partial correlation and multiple regression analyses were used to further explore the relationship between neonatal RSA maturation and school-age social competence. Results support the hypothesis that early central nervous system self-regulatory abilities, as assessed by RSA measures, are predictive of later complex behaviors.

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Assessed the relation of behavioral codes of quiet versus active sleep state to neonatal health status in 62 very low birth weight preterm neonates. Sleep sessions (12 min) were coded for percentage time in active versus quiet sleep at 33, 34, and 35 weeks conceptional age. ECG was monitored during each sleep session to derive measures of heart rate, heart rate variability, and an index of cardiac vagal tone derived from respiratory sinus arrhythmia. Higher risk neonates spent more sleep session time in active sleep than healthier preterm neonates. Cardiac vagal tone showed a maturational change during the study weeks, whereas percentage of sampled sleep time in active sleep did not. Vagal maturation measured by age-related increases in the amplitude of respiratory sinus arrhythmia was associated with less active sleep overall, although weekly measures of respiratory sinus arrhythmia and sleep state were not related. Follow-up data on 30 of the neonates indicated that heart rate variability and cardiac vagal tone, but not sleep state measures, were related to better outcomes in mental processing, social skills, and motor skills, and to fewer behavior problems. Results are discussed in terms of the lack of coupling between behavioral and physiological components of preterm sleep states at this age as compared with that seen in full-term sleep states.

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