Abstract □ 75

1. Future SIDS infants : To determine the influence of sleep stages and nighttime distribution on cardiac autonomic activity (ANS) and to evaluate changes in ANS controls in response to obstructive events in future victims of SIDS, we studied the polysomnographic sleep recordings of 18 future SIDS infants and those of 36 matched control infants. Autoregressive spectral analyses of heart rate (HR) was evaluated as a function of sleep stages and was performed preceding and following the obstructive apneas. High-frequency component (HF) reflected parasympathetic tonus. The low frequency to high frequency power ratio (LF/HF) was computed to evaluate sympathovagal balance.

Results : In both NREM and REM sleep, SIDS infants were characterized by significantly lower normalized HF powers, and higher LF/HF ratios.

Compared to preapnea values, LF/HF power ratios significantly decreased after obstructive apneas in control infants, but not in the future SIDS victims.

2. Environmental factors The incidence of SIDS has been linked to environmental factors such as prone body position, high environmental temperature or maternal smoking. The objective of these studies were to evaluate, in 24 healthy neonates and infants, the effects of body position (prone versus supine position), ambient temperature (20°C-25°C-30°C), and maternal smoking on ANS and polygraphic auditory arousal thresholds. Neonates and infants were studied polygraphically for one night.

Results : Especially in REM sleep, the 3 environmental factors decreased parasympathetic tonus and increased auditory arousal thresholds in REM sleep.

Conclusion : Future SIDS victims were characterized by lower parasympathetic tonus and decreased autonomic responses to obstructive events during sleep.

Prone body position, high ambient temperature, maternal smoking decreased parasympathetic tonus a decreased arousability to auditory stimuli.

Autonomic nervous system is implicated in the mechanisms of arousability. Autonomic dysfunction could be implicated in arousal deficiency. These findings could be relevant to mechanisms implicated in SIDS.