Effects of auditory stimulation on heart rate in premature infants as a function of level of arousal, probability of CNS damage, and conceptional age

In 2 experiments, heart rate responses of newborn infants to an auditory stimulus as a function of sleep vs wakefulness, probability of perinatal impairment of the central nervous system, and developmental level were compared. All subjects were studied under standard conditions, in their own incubators, using an 80 dB (re 0.02 dynes/cm²) low-frequency buzzer of 3-sec duration. Heart rate responses were averaged over 10 trials for each subject in each state. In the first study, which compared the responses of high- and low-risk subjects of 1800 gm or greater weight, it was found that there was no difference between the groups in the response during sleep; or greater weight, it was found that there was no difference between the groups in the response during sleep; during wakefulness, however, a significant difference in the direction of response was found. High-risk subjects accelerated, as in sleep, whereas low-risk subjects decelerated. In a developmental study of 4 small premature infants, it was found that the direction of the waking heart rate response changed from acceleration to deceleration at about 35 to 36 weeks conceptional age.