Preschoolers' daytime respiratory sinus arrhythmia and nighttime sleep.

We examined the association between preschoolers' (N=29; 20 boys; M age = 3.99 years, SD=.69) daytime parasympathetic nervous system (PNS) activity indexed by respiratory sinus arrhythmia (RSA) and their nighttime sleep. Children's baseline RSA was assessed in the laboratory. Sleep was monitored for seven consecutive nights at the child's home via actigraphy and the following sleep parameters were derived: sleep minutes, sleep activity index and sleep efficiency. Regression analyses showed that after controlling for potential confounds, higher RSA was a predictor of lower sleep activity and higher sleep efficiency. Results highlight the importance of physiological regulation for the sleep of healthy preschool children.