Maturation of the Cardiac Response to Sound in High-Risk Preterm Infants

Noise is considered a potential source of stress in the neonatal intensive care unit (NICU); yet, it is unknown how preterm infants habituate to sound in the NICU. Heart rate responses to sound were evaluated in 12 preterm infants from 32 weeks' gestational age through hospital discharge. Heart rate response changes to auditory stimuli were recorded for 10 habituation and 10 dishabituation trials. Significant heart rate deceleration began to appear by 34 weeks postconceptional age. With weeks 32 to 38 combined, a significant response was noted for the novel response. Responses differed significantly for weeks 34, 35, and 36. Infants at 36 weeks had a significant heart rate response at T17 to T20, suggesting anticipation of a third stimulus. Infants with higher Apgar 5 scores had smaller heart rate responses. Findings suggest that preterm infants, especially those with lower Apgar scores, may be vulnerable to larger heart rate changes in response to sound and may require additional consideration.