Human Auditory Steady-State Responses during Repeated Exposure to Hypobaric Hypoxia

Abstract

This study was aimed at evaluating the time course of auditory steady-state response (SSR) variations during two consecutive exposures to hypobaric hypoxia. Six normal subjects were examined in a hypobaric chamber at ground level. Then, they climbed to a simulated altitude of 17000 ft (5182 m), where SSRs were recorded after 6, 12, 18, 24 and 30 min. Thereafter, they breathed 100% O₂ and SSRs were recorded after 2 min of reoxygenation. A second exposure to hypoxia followed, with SSR recordings after 6 and 12 min. Finally, the subjects returned to ground level for recovery recording. A phase shift of SSR sinus wave was observed at the beginning of both exposures to hypoxia, although in the first recording (i.e. at 6 min) during the first exposure, the result was not statistically significant. A slight SSR phase shift was still detectable on return to ground level. The central acoustic pathway involved in SSR genesis was probably the area which was found to be most sensitive to hypoxia, compared to other parts of the auditory apparatus (e.g. the cochlea). This data could suggest an impairment of compensation mechanisms when consecutive exposures to hypoxia are performed.

Effects of Acute Hypoxia on Early Visual and Auditory Evoked Potentials

“…Auditory brain-stem responses (ABRs) occur within 10 ms after stimulus presentation, and studies have found that acute hypobaric hypoxia impaired ABRs at 17,000 ft ( Urbani and Lucertini, 1994 ) and 14,750 ft ( Hayashi et al, 2005 ). In addition, the latency of auditory steady-state responses has been found to increase after consecutive hypobaric hypoxia exposures at a simulated altitude of 17,000 ft ( Lucertini et al, 2002 ). Middle latency auditory evoked potentials occurring between approximately 10–80 ms after stimulus presentation, in contrast, may be relatively less sensitive to hypoxia ( Lucertini et al, 1993 ; Bouchet et al, 1997 ).…”

Auditory function in humans at high altitude. A scoping review

“…In five studies conditions of HH were simulated, while the remaining four studies were performed under NH. Three studies (two in HH [ 10 , 36 ] and one in NH [ 37 ]) used PTA, one study in HH analyzed OAE [ 13 ], and five studies (two in HH [ 12 , 14 ] and three in NH [ 2 , 38 , 39 ]) analyzed AER. All these studies had an exposure time of less than six hours.…”

“…Focusing on studies analyzing EEG-based measurements, Lucertini et al investigated auditory SSR in six male healthy volunteers at MSL and during a 30 min stay at a simulated altitude of ~5200 m [ 14 ]. Auditory SSR was also measured at altitude after two minutes of re-oxygenation, when the mask was taken off.…”

“…Together with the variability of the protocols, a limitation affecting several studies included in the present review is the small sample size of the analyzed population, where nine of 17 studies presented a study population equal to or less than 15 subjects. This factor, combined with large inter-individual variability related to demographic and physiological aspects (e.g., variability in oxygen transfer system, chemoreceptor sensitivity, respiratory activity, and hypoxia-induced hyperventilation [ 14 , 16 ]), may explain variable results among studies or non-significance of changes (e.g., for AER amplitude). Demographic variability could be partially tackled by restricting enrollment to selected population (e.g., military aviators or trekkers), although this may limit the extension of the results to the general population.…”

Physical and Physiological Effects on Otoacoustic Emissions in Hypobaric Hypoxia

“…However, the I-V wave interval measured during recovery from hypoxemia was shortened. Lucertini et al [14,15] reported prolonged latencies of steady-state responses under the same conditions (5,182 m).…”