Cochlear hypoxia and the compound action potentials.

A relatively restricted area, including the ear, was perfused in guinea pigs with hypoxic blood having a pO2 of 10, 20, and 30 mm Hg, respectively. The changes induced to the cochlear action potentials were analyzed and the results compared with those obtained in a previous study in which the guinea pigs were rendered hypoxemic by ventilating them with air entrapped in a closed circuit from which the CO2 was continuously absorbed. The changes induced to the cochlear action potentials by both methods were very similar. However, while using the territorial model for inducing hypoxia, 75% of the animals showed a threshold shift at a blood pO2 of 20 mm Hg and with the general model all the animals showed a threshold shift at 25 mm Hg blood pO2. In other words, if the hypoxic condition affected the whole body, other factors such as a slight, but continuous tendency to acidosis with significant increase in blood lactic acid concentration could join the oxygen deficit in affecting cochlear function.