Brainstem Auditory Impairment in Very Preterm Infants who Experience Chronic Sublethal Hypoxia

Very preterm infants who suffer from bronchopulmonary dysplasia (BPD), a major neonatal complication, often experience frequent episodes of hypoxaemia or prolonged hypoxaemia, resulting in significant chronic sublethal hypoxia (CSH). Whether the CSH occurring during the neonatal period exerts any adverse effect on the immature brainstem auditory system remains a topic of attracting considerable interest. With brainstem auditory evoked response (BAER) and particularly maximum length sequence (MLS) BAER, recent investigators have revealed that neonatal BPD damages functional integrity of the immature brainstem auditory system. There are significant abnormalities in the BAER components that reflect central neural function of the auditory brainstem. By comparison, there are only mild abnormalities in the BAER components that reflect peripheral neural function of the auditory brainstem. Clearly, CSH associated with neonatal BPD damage central neural conduction, suggesting impaired myelination and synaptic dysfunction, in the immature auditory brainstem, but exerts limited effect on peripheral neural function of the brainstem. These abnormalities tended to be improved after term date. CSH occurring during the neonatal period damages myelination of the central auditory system, which tends to be alleviated after term date.