Brainstem auditory evoked responses in the newborn lamb. Studies during postnatal development and acute hypoxia

Brainstem auditory evoked responses (BAER) have been studied in several species and have provided a neurophysiologic 'window' into brainstem function. We have pursued further studies in the newborn lamb and adult sheep. BAER amplitude increased as the stimulus intensity increased from 45 to 95 dB and as the click frequency decreased from 88.8 to 22.2 Hz. BAER latency increased as both the stimulus intensity decreased and the click frequency increased. Developmental studies were performed between the 2nd and 35th day of life in the newborn lamb. No significant change in either latency, amplitude, or wave morphology was noted in contrast to other species where developmental changes are prominent. This was due to both the prenatal maturation of the lamb's brain and to the relatively short interval of the postnatal studies. We also studied the effect of prolonged severe hypoxia and acidosis on the BAER in the newborn lamb and found no significant change in either the amplitude or latency of the response.