Influence of Variations of O 2 and CO 2 Tension in Inspired Air Upon Hearing

Abstract

Although tests made on aviators and other observations at high altitudes indicate that O₂-lack causes sensory disturbances, 1 particularly in vision, no systematic study seems to have been made in which the influence of various O₂- and CO₂-tensions was investigated in regard to sensory functions. Such a study seems to be of particular interest since the importance of these factors for various reflexes is well known. The present paper is based upon 96 audiometer experiments carried out on 6 thoroughly trained subjects. The administration of various O₂-, N₂- and CO₂-air mixtures, which were inhaled from several large Douglas bags, was preceded and followed by control periods in which the threshold for a certain sound was determined in intervals varying between 1 and 4 minutes. Long control series extending over several hours were also carried out in order to determine the spontaneously occurring variations in threshold. The observation room was nearly sound proof.

In 37 experiments the influence of breathing CO₂-air mixtures (2%-8.4%) during 5-22 minutes was studied upon the threshold of C 128, C 2048, and C 4096 cycles per second. It was found that a distinct hearing loss occurred during CO₂ breathing at and above 3% CO₂. Depending on the CO₂ concentration and the duration of the breathing period, the recovery after the end of the CO₂-period varies somewhat, but in general it was found that in less than 15 minutes the threshold was the same as before the experiment.

Contrary to expectation, similar losses in auditory acuity were obtained in 26 experiments in which the CO₂ tension of the blood was lowered by means of voluntary hyperpnea which was carried out for 3-6 minutes. The threshold determined immediately after the hyperpnea period during which apnea obtained was considerably higher and a gradual return to normal was observed during the next 10-15 minutes.