HEART-RATE AND HEART-RATE-VARIABILITY DURING SLEEP IN SMALL-FOR-GESTATIONAL-AGE NEWBORNS

To assess the influence of intrauterine growth retardation on heart ra te (HR) and HR variability during sleep, we performed polygraphic reco rdings in 10 small-for-gestational age (SGA) and 16 appropriate-for-ge stational age (AGA) newborns. Both groups were clinically and neurolog ically normal and were at 37 to 41 wk conceptional age. RR intervals w ere analyzed using the short-time Fourier transform in three frequency bands: 1) high frequency, with a period 3-8 heartbeat; 2) mid frequen cy, with a period 10-25 heartbeat; and 3) low frequency, with a period 30-100 heartbeat. In both active and quiet sleep, SGA newborns signif icantly differed from AGA newborns by having a shorter RR interval(p < 0.01) and lower amplitude of HR variability in all bands (p < 0.05) e xcept low frequency in quiet sleep. Quiet sleep differed from active s leep by having a longer RR interval (p < 0.05), higher high-frequency variability (p < 0.02) in both SGA and AGA newborns, and lower low-fre quency variability (p < 0.005 for AGA newborns). Our data give evidenc e of clear modifications of both sympathetic and parasympathetic HR co ntrol in the at-risk SGA population. Similarity of between-state chara cteristics suggests maintained CNS control of HR in SGA as well as in AGA newborns. We speculate that between-group HR and HR variability di fferences may be related to augmented metabolic rate in SGA compared w ith AGA newborns.