Variation of Endocochlear Po2 and Cochlear Potentials by Breathing Carbon Dioxide

Abstract

The effect of carbon dioxide on oxygen tension in the endolymph was determined by the micropolarographic technique. Different concentrations (5% and 10% CO₂) and different exposure times (3, 5, and 20 minutes) were investigated. The highest levels of Po₂ in the endolymph (101.7, 93.9 and 69.5 mm Hg) were accomplished by respiration of 10% CO₂, 90% O₂, for 20, 5, and 3 minutes consecutively. The lowest Po₂ increase, 50.7 mm Hg was observed after breathing 5% CO₂, 90% O₂ for 20 minutes. Extreme hypercapnia caused an increase of endocochlear potentials (EP) in all groups. In the second group EP increased from +79.3 to +84.9 and in all groups they had returned to the pretreatment level after CO₂ discontinuation. These results support the theory that carbonic anhydrase participates in the generation of EP. At the same time that EP increased, cochlear microphonics declined and opposite after the breathing mixture was discontinued. The results permit the conclusion that high levels of Po₂ in endolymph is achievable even with short periods of respiration with high CO₂ mixture, and suggest the role of carbonic anhydrase during EP generation.