Physiological relationship between autonomic reactions and arousals in infancy.

Objective: Changes in blood pressure (BP) were measured following auditory stimuli in the prone and the supine position to study the correlation between arousal from sleep and autonomic responses.

Method: Two newborns born at term, two infants and four children were recorded polygraphically during one night, while sleeping in the prone and the supine position. They were exposed to white noises of increasing intensities during both rapid eye movement (REM) and non-rapid eye movement (NREM) sleep in each position. BP changes were measured by Finapress in the children and by pulse transient time (PTT) in the infants and newborns.

Results: Basal systolic BP pressures were lower (P<0.001) and PTT were higher (P=0.008) in the prone than in the supine position in children and in infants. Following the auditory stimulations, the increases in systolic BP (P=0.024) and the decreases in PTT (P=0.006) were smaller in prone than in supine position. During cortical arousals, the same findings were found, independently of sleep stages.

Conclusion: Compared with when they are sleeping supine, children and infants sleeping prone had lower basal BP and higher PTT and smaller changes in BP and PTT after auditory stimulation. Reduced BP changes to stimuli could be implicated in the increased arousal thresholds in prone position.