Phasic heart rate responses: different patterns in black and in white newborns.

Click stimuli were presented during sleep to newborns from a low socioeconomic class urban population in Northeastern United States. Eighty-three black newborns showed less immediate poststimulus deceleration than did 67 white newborns. This difference was independent of heart rate level, and could not be accounted for by any of the perinatal variables studied, including birthweight and gestational age. These results suggest that in this population, black newborns differ from white newborns in the pattern of phasic heart rate responses to stimuli. This constitutes evidence for an additional difference in heart rate regulation in black as compared to white newborns from this population, since prior work reported differences in tonic heart rate level during sleep between black and white newborns.