Reduction of Acoustically-Induced Auditory Impairment by Inhalation of Carbogen Gas:I. Permanent Noise-induced Cochlear Damage

Abstract

The possible beneficial effects of carbogen gas (95 % O₂/5 % CO₂) inhalation on noise-induced permanent cochlear impairment were investigated. Groups of guinea pigs were exposed to daily 3-hour presentations of 120 dB of broad-band noise in an atmosphere of either carbogen gas or normal air. Other groups received carbogen or normal air with a low intensity (50 dB) acoustic exposure. After a 30-day stabilization period each ear was examined electrophysiologically and histologically. Measures included a.c. cochlear potentials from 100 Hz through 20 kHz as well as counts of missing inner hair cells (IHCs) and outer hair cells (OHCs). Statistically significant improvement in the 1 muv isopotential function of the a.c. cochlear potential over all test frequencies and significant reduction in the number of missing IHCs and OHCs was found to result from inhalation of carbogen gas. Blood gas analysis demonstrated a rapid and marked elevation in arterial PCO₂ and PO₂ with a corresponding drop in pH to result from inhalation of carbogen. The vasodilating effects of increased arterial carbon dioxide tension are discussed in terms of current speculations regarding the role of vasoconstriction in noise-induced hearing loss.

Statistisch bedeutsame Verbesserung in der 1 muv isopo-tentialen Funktion des Cochlea-Wechselstrompotentials uber das Spektrum aller Frequenzen und eine bedeutsame Reduktion in der Anzahl verlorengegangener innerer und auuszerer Haarzellen wurde als Folge der Inhalation von Kohlendioxydgas festgestellt. Die Blutgasanalyse zeigte einen schnellen und erheblichen Anstieg des arteriellen PCO₂ und PO₂ verbunden mit einem entsprechenden Fall des pH als Folge der Inhalation von Kohlendioxydgas. Die gefauszerweiternde Wirkung erhouhter Kohlendioxyd-spannung im Blut wird diskutiert besonders im Hinblick gegenwaurtiger Spekulationen uuber die Rolle der Gefauszver-engung im Falle des durch Laurm verursachten Hourver-lusts.