Hearing Aids Performance in Hypobaric Environments.

OBJECTIVE: High altitudes imply exposure to a decreased ambient air pressure. Such a situation may also alter the performance of acoustic transducers using vibrating diaphragms due to air rarefaction. This study aimed at analyzing the performance at high altitude of hearing aids (HAs) where mechano-electric and electro-mechanic transducers are used. METHODS: A hypobaric chamber was used to perform two separated experimental sessions. In the first one two commercial models of HAs were exposed to a simulated altitude of 25,000 ft (7620 m) and to a subsequent rapid decompression profile, with a rapid climb (< 3 s) from 8000 (2438 m) to 25,000 ft. The second session separately analyzed the performance of microphone and receiver at an altitude of 9000 and 15,000 ft (2743 and 4572 m). Before and after the first session, the HAs were tested with an electronic ear while a dedicated recording system was used in the second session. RESULTS: No HA damage or dysfunction was detected during the first session. In the second one, the microphone showed a mild decrease of its output, while the receiver exhibited a much higher reduction of its output. CONCLUSION: Our findings highlight the safe use of HAs even under extreme environmental pressure changes. For altitudes exceeding 10,000 ft (3048 m), a recalibration of the HAs output via a dedicated program may be suggested. Lucertini M, Sanjust F, Manca R, Cerini L, Lucertini L, Sisto R. Hearing aids performance in hypobaric environments. Aerosp Med Hum Perform. 2021; 92(9):738743.

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.

High Altitude Performance of Loudspeakers and Potential Impact on Audiometric Findings.

BACKGROUND: The evaluation of how air rarefaction can affect a loudspeaker performance at altitude implies the need for characterization of earphones during hypobaric conditions. The aim of this study was phonometric analysis at different altitudes of the acoustic output of a widely used earphone model, along with its consequences on audiological investigations conducted under such environmental conditions.METHODS: The transfer function of a TDH-39P earphone was analyzed with an artificial ear under nine different altitude levels, from sea level up to 35,000 ft, inside a hypobaric chamber. A specific phonometric system not sensitive to environmental pressure changes was used. Other potentially confounding factors, such as environmental temperature and humidity, were continuously monitored.RESULTS: No relevant temperature or humidity changes were detected. The sound pressure level generated by the earphone under hypobaric conditions was found considerably affected by air density changes. These data produced a correction table aiming at recalibrating the earphone's output at each audiometric octave test frequency within the 250-8000 Hz range. Quite different characteristics of response were observed at different audiometric frequencies. Such findings were particularly evident for altitudes exceeding 12,000 ft.DISCUSSION: The development of a frequency-selective and altitude-related correction factor for acoustic stimuli is an essential aspect when hearing threshold measurements in hypobaric environments are performed.Lucertini M, Botti T, Sanjust F, Cerini L, Autore A, Lucertini L, Sisto R. High altitude performance of loudspeakers and potential impact on audiometric findings. Aerosp Med Hum Perform. 2019; 90(7):655-659.