Cardiac responding to auditory stimuli in newborn infants: Why pacifiers should not be used when heart rate is the major dependent variable

For more than a decade, studies of neonatal heart rate responding to various stimuli have commonly used pacifiers to control or maintain state. Recent evidence suggests that neonatal heart rate accelerates during sucking, and that cardiac changes evoked by sucking may affect concomitant cardiac responses to stimulation. The present study examined heart rate responses of 16 awake newborns to a 72 db auditory stimulus presented at four different times in relation to ongoing nonnutritive sucking activity: just before a sucking burst, early in a burst, late in a burst, and just after a burst. In addition, heart rate changes were examined during an intertrial sucking burst of selected duration. Intertrial results indicated that rapid, 10 bpm heart rate accelerations and decelerations occurred at the onset and offset of nonnutritive sucking, respectively. Heart rate changes in relation to tones were either acceleratory or deceleratory, depending on the nature of ongoing sucking activity. The results indicated that precise cardiac-somatic coupling may occur in the newborn, and that future studies of neonatal heart rate responding should avoid the use of pacifiers to control state.