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Hearing loss in space.

BACKGROUND
Temporary and, in some cases, permanent hearing loss has been documented after long-duration spaceflights.


METHODS
We examined all existing published data on hearing loss after space missions to characterize the losses.


RESULTS
Data from Russian missions suggest that the hearing loss, when it occurs, affects mainly mid to high frequencies and that using hearing protection often might prevent the loss. Several significant questions remain about hearing loss in space. While the hearing loss has been presumed to be noise-induced, no clear link has been established between noise exposure and hearing loss during spaceflight. In one documented case of temporary hearing loss from the Shuttle-Mir program, the pattern of loss was atypical for a noise-induced loss. Continuous noise levels that have been measured on the Mir and previous space stations, while above engineering standards, are not at levels usually associated with hearing loss in ground-based studies (which have usually been limited to 8-10 h exposure periods). Attempts to measure hearing in space using threshold-based audiograms have been unsuccessful in both the American and Russian programs due to noise interference with the measurements.


CONCLUSIONS
The existing data highlight the need for reliable monitoring of both hearing and noise in long-duration spaceflight.