Effects of sleep position, sleep state and age on heart rate responses following provoked arousal in term infants.

Previous studies have suggested that autonomic dysfunction may be involved in Sudden Infant Death Syndrome (SIDS). The major risk factors for SIDS are the prone sleeping position and maternal smoking. Our aim was to examine the effects of sleeping position and maternal smoking on the postnatal maturation of autonomic function by examining heart rate responses following arousal in healthy term infants. Twenty-four infants (11 born to mothers who smoked during pregnancy and 13 to mother who did not smoke) were studied using daytime polysomnography and multiple measurements of arousal threshold (cm H(2)O) in response to air-jet stimulation applied alternately to the nares were made in both active sleep (AS) and quiet sleep (QS). We demonstrated no difference between smoking and non-smoking groups of infants in any of our measurements, and thus combined data from the groups. Baseline (BHR) was elevated in the prone compared to the supine position in quiet sleep (QS) at 2-3 weeks (p<0.001) and 5-6 months (p<0.001), and in active sleep (AS) at 2-3 and 5-6 months (p<0.05). BHR was significantly elevated in AS compared to QS in the supine position at all ages (p<0.01) and in the prone position at 2-3 (p<0.001) and 5-6 months (p<0.05). Increases in heart rate (deltaHR%) following arousal were significantly greater in the supine compared to the prone position in QS at 2-3 weeks (p<0.05) and in AS at both 2-3 (p<0.01) and 5-6 months (p<0.05). DeltaHR% was significantly greater in AS compared to QS in both supine (p<0.05) and prone (p<0.001) positions at 2-3 weeks and in the supine position at 2-3 months (p<0.001). We conclude that sleep state, sleep position and postnatal age affect the cardiac responses following arousal from sleep in healthy term infants. Impairment of heart rate control in the prone position may be important in understanding the increased risk for SIDS in this position.