Earlier studies addressing the influence of sleep position on sleep did not examine, in detail, infants' sleep characteristics. Except in one earlier study (Masterson, J et al., Pediatrics, 1987), most reports concern full term infants. We examined sleep position effects on sleep characteristics in our preterm population at discharge (see also abstract by Adams, M et al.). The purpose of this study was to determine, in the same population of infants, if sleep position particularly affects the first sleep cycle after feeding.

We studied 16 infants at a mean post-conceptional age of 36.5±0.6 weeks. The infants (mean gestational age 32.2±3 weeks; mean birth weight 1733±135 g) were all recorded with videopolysomnography (VPSG) for 6 hours (two consecutive daytime nap periods). VPSG was scored for Active Sleep (AS), Quiet Sleep (QS), Indeterminate Sleep and Total Sleep Time. Arousal was defined as body movement, cry or eye opening lasting 10-60 seconds. An arousal > 60 seconds was scored as an awakening. Indices were calculated as number of arousals or awakenings per 100 minutes. The first sleep cycle was evaluated for each position.

We found the length of the first QS to be significantly longer in the prone position. Awakenings were less frequent during both the first AS and the first QS in the prone position. The longest bouts (MaxBout) of both AS and QS during the first sleep cycle were longer in the prone position.

We are currently analyzing heart rate variability during the first sleep cycle in this population. Five of these recordings, at present, are analyzed. Heart rate variability during the first quiet sleep was significantly lower in prone compared with supine sleep position (mean±SD = 2.4±1.4 v.3.0±1.4 respectively, p= 0.025, Wilcoxon). We conclude that longer QS, fewer awakenings, and less heart rate variability are more likely to occur immediately following feedings, especially when the infant is prone. The mechanism for this difference is unclear but may be related to the increased metabolic rate associated with specific dynamic action of food assimilation. (Table shows means and SDs)

Table 1 No caption available.
Full size table