The effect of race and of socioeconomic class upon heart rate and systolic blood pressure distributions was examined in 247 full-term, appropriate birth weight newborns. For each newborn, heart rate and blood pressure measurements obtained during all of the non-rapid-eye-movement (NREM) periods of sleep in a single test session were each averaged. Heart rate was significantly faster in black newborns than in white newborns, and this racial difference in heart rate was similar in upper socioeconomic class subjects as in lower socioeconomic class subjects. Newborn systolic blood pressure did not vary as a function of race or of socioeconomic class. Systolic blood pressure correlated positively with the number of feedings from birth, the total fluid intake from birth, and the total sodium ingested from birth.

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Sixty-one full-term, appropriate-weight black newborns had higher heart rates, replicating a racial heart rate difference, but did not differ significantly in systolic blood pressure from 71 white newborns. Systolic blood pressure in the newborn is related both to the total number of feedings from birth and to the total fluid intake.

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.