Changes in cochlear oxygenation, microcirculation and auditory function during prolonged general hypoxia.

Changes in cochlear microcirculation and oxygenation and auditory function were examined in anesthetized guinea pigs during prolonged hypoxic ventilation (8% oxygen in nitrogen) for 1 h. Cochlear blood flow and perilymphatic oxygen partial pressure were measured using laser Doppler flowmetry and oxygen-sensitive microelectrodes. Auditory function was examined by recording cochlear microphonics, compound action potentials and auditory evoked brainstem response. Blood pressure and heart rate were monitored. During systemic hypoxia, the perilymphatic PO2 dropped on average to about 70% of the initial value. Cochlear and brainstem potentials showed a mean reduction to 75-82%. Different effects of hypoxia on cochlear blood flow were observed and included decreases as well as increases. Mean arterial blood pressure declined significantly during hypoxia, while the heart rate remained constant. The changed variables returned to normal during reventilation with room air. The findings are discussed with regard to their significance as an animal model for the study of hypoxia-induced cochlear pathophysiology.