Behavioral sleep states in very low birth weight preterm neonates: relation to neonatal health and vagal maturation.

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.