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

BACKGROUND: 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.METHODS: 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 (Sao2). The PTA data obtained at high altitude were corrected according to a specific recalibration table.RESULTS: 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 Sao2 levels was observed.DISCUSSION: 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.Lucertini M, Lancia S, Sanjust F, Guadagno AG, Lucertini L, Sisto R. Lack of significant audiometric changes under hypobaric hypoxia at 15,000 ft. Aerosp Med Hum Perform. 2020; 91(1):32-36.

Visual function at altitude under night vision assisted conditions.

INTRODUCTION: Hypoxia, even mild, is known to produce negative effects on visual function, including decreased visual acuity and sensitivity to contrast, mostly in low light. This is of special concern when night vision devices (NVDs) are used during flight because they also provide poor images in terms of resolution and contrast. METHODS: While wearing NVDs in low light conditions, 16 healthy male aviators were exposed to a simulated altitude of 12,500 ft in a hypobaric chamber. RESULTS: Snellen visual acuity decreased in normal light from 28.5 +/- 4.2/20 (normoxia) to 37.2 +/- 7.4/20 (hypoxia) and, in low light, from 33.8 +/- 6.1/20 (normoxia) to 42.2 +/- 8.4/20 (hypoxia), both at a significant level. An association was found between blood oxygen saturation and visual acuity without significance. No changes occurred in terms of sensitivity to contrast. DISCUSSION: Our data demonstrate that mild hypoxia is capable of affecting visual acuity and the photopic/high mesopic range of NVD-aided vision. This may be due to several reasons, including the sensitivity to hypoxia of photoreceptors and other retinal cells. Contrast sensitivity is possibly preserved under NVD-aided vision due to its dependency on the goggles' gain.