Effects of an Hypoxia at 5% Oxygen on Global Electrophysiqlogical Responses from Normal and Hmropic Ears of Awake Guinea Pigs

In the continuation of our studies on the involvement of blood supply deficiencies in various experimental pathologies of the inner ear we have conducteaa study on the effects of transient hypoxia on normal and hydropic ears. In the same study we investigated the possible protective effects of an antiischemic drug. All experiments were conducted on awake guinea pigs warranting a normal physiological functioning of the circulatory system. Global electrophysioIogical responses from the inner ear were monitored: cochlear microphonic, summating potential and auditory nerve compound action potential. In normal ears hypoxia induced a threshold elevation a t all frequencies thus affecting the whole cochlea, and also very large diminutions of action potential amplitude evoked a t high intensity level exclusively in response to a high frequency. Hydropic ears presented a n hypersensity to anoxia, their action potential amplitude being affected a t more stimulus frequencies and presenting a much slower recovery process, but their threshold elevations were similar to those of normal ears. The drug treatment limited the decrease of action potential amplitude in normals, but no such effect was observed for hydropic ears.