Cochlear hypoxia and the compound action potentials

A relatively restricted area, including the ear, was perfused in guinea pigs with hypoxic blood having a CO₂ 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 continously 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.