Lack of Significant Audiometric Changes Under Hypobaric Hypoxia at 15,000 ft.

The aim of this study was pure tone audiometry (PTA) evaluation in normal individuals exposed to hypobaric hypoxia, taking into account the influence of air rarefaction on sound transmission via a standard earphone. The study was conducted in a hypobaric chamber using a standard audiometer and a TDH-39P earphone whose performance at altitudes was analyzed in a previous research. Eight male volunteers underwent PTA testing at ground level and at 15,000 ft under normoxia (via an oxygen mask) and after 20 min of hypoxia. Auditory threshold at 500, 1000, 2000, and 4000 Hz was recorded from the right ear while monitoring arterial oxygen saturation (So₂). The PTA data obtained at high altitude were corrected according to a specific recalibration table. During hypoxia, a significant threshold shift was observed only at 4000 Hz, with respect to ground level recording, for the sole not-corrected data. At the same frequency a significant threshold shift was also observed between the ground level recording and normoxia at 15,000 ft, confirming the presence of a hypobaric effect not related to hypoxia. After the recalibration procedure, this hearing impairment was not significant. No correlation with So₂ levels was observed. The mild and not significant presence of high altitude-induced PTA derangements in healthy normal individuals was documented, although a stimulus recalibration was needed for a correct interpretation of our data.