Effects of Carbon Dioxide in the Middle Ear Cavity upon the Cochlear Potentials and Cochlear pH

Abstract

To elucidate the effects of CO₂ in the middle ear upon the cochlea, measurements were made of the cochlear potentials (compound action potential and endocochlear potential) and of the pH of the inner ear fluids and the organ of Corti. Gas containing CO₂ did not affect the AP threshold, except for a slight decrease in AP threshold elicited by an 8 kHz tone burst with 10% CO₂ flow. The EP did not vary with CO₂ gas. The CO₂ gas mixture reduced the pH in perilymph significantly, by 0.11± 0.05 with 5% CO₂ and by 0.17±0.04 with 10% CO₂, in comparison with 100% N₂. The CO₂ gas slightly but significantly decreased the endolymph pH, by 0.05±0.04 with 5% CO₂ and by 0.09±0.06 with 10% CO₂. The removal of perilymph led to a greater acidification of endolymph with CO₂ gas. Acidification of the organ of Corti was also noted with the CO₂ gas flush. These findings indicate that CO₂ in the middle ear influences the acid-base regulation of inner ear fluids and the cochlear function.

Key Words:

• pH-selective microelectrode
• action potential
• endocochlear potential
• chinchilla