Study objectives: To determine the effects of sleeping position on development of circulatory control in infants over the first 6 months of postnatal age (PNA).
Design: Effects of sleeping position, sleep state and PNA on beat-beat heart rate (HR) and mean arterial pressure (MAP) responses to a head-up tilt (HUT) were assessed during sleep in infants at 2-4 wks, 2-3 mo and 5-6 mo PNA.
Measurements: Daytime polysomnography was performed on 20 full-term infants (12 F/8 M) and MAP was recorded continuously and noninvasively (Finometer). HUTs of 15 degrees were performed during active sleep (AS) and quiet sleep (QS) in both the prone and supine sleeping positions. MAP and HR data were expressed as the percentage change from baseline, and responses were divided into initial, middle and late phases.
Results: In the supine position HUT usually resulted in an initial increase (P < 0.05) in HR and MAP, followed by decreases (P < 0.05) in HR and MAP in the middle phase; subsequently HR and MAP returned to baseline in the late phase. By contrast, in the prone position the initial HUT-induced rises in HR and MAP were usually absent, and at 2-3 mo MAP actually decreased (P < 0.05); subsequently HR but not MAP returned to baseline. At 2-3 mo, MAP was lower (P < 0.05) in prone than supine sleeping throughout the HUT.
Conclusions: Prone sleeping alters MAP responses to a HUT during QS at 2-3 mo PNA. Decreased autonomic responsiveness may contribute to the increased risk for SIDS of infants sleeping in the prone position.