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Experiments were conducted to test the hypothesis that intermittent exposure to oxygen at two atmospheres absolute (2 ATA) could delay the onset of pulmonary toxicity. This paper reports effects of 2 ATA O2 (total exposure time of 14.1–19.3 h) upon the auditory and vestibular systems of five diver volunteers and effects of a normoxic N2O2 mix on a sixth. Immediately after exposure four subjects had increased acuity by air conduction in the mid-frequency range. Bone conduction sensitivity increased for all six subjects. Middie-ear reflexes were depressed or absent with only partial recovery one month after the experiment for the O2-breathing subjects, but were more sensitive after exposure for the subject breathing N2O2. Middle-ear pressures grew markedly more variable for O2 subjects up to 72 h postexposure, implying decreased eustachian tube function from oxygen. Vestibular systems of four O2-exposed subjects and the N2O2 subject were markedly suppressed to caloric stimulation after exposure, implying pressure as the contributory cause. Operational application may be found in possibly sensitizing certain frequencies to improve the listener's ability to detect signals in noise. [Work supported by CIC, NRMC. and COMSUBDEVGRU ONE.]

Tympanometric measurements are versatile and accurate when more than one type of ear disease is present. Three cases are presented where information from tympanometry beyond that derived from otological and routine audiological testing yielded accurate diagnoses. A patient with a history of middle-ear disease presented with a sensori-neural loss. Measures of static conductance correctly identified the problem as stiffness of the ossicular chain. An infant with unilateral congenital atresia and questionable hearing in her normal-appearing ear was determined to have serous otitis media by tympanometry and reflex testing. The course of the disease was monitored and reversed. A 17-year-old female suffered a basal skull fracture with a sudden conductive hearing loss. Low conductance and high impedance correctly identified loss of mobility of the ossicular chain which was confirmed surgically. These three cases illustrate the advantages of tympanometry in making rapid, accurate, objective measurements involving complex diagnoses of middle-ear function.