Formal hearing conservation efforts (e.g., training in hearing protection and effects of noise, enforcement of hearing protection use) have been aimed at all astronauts, but only those comparison participants who worked in noise-hazardous jobs at the NASA Johnson Space Center (JSC). Consequently, it would be logical to assume that the astronauts, as the target population of the conservation efforts, were more at risk for and would show more NIHL as compared to the comparison participants. However, the analysis of the data yielded surprising results.
A hearing threshold is the lowest sound level that is detected from a specific percentage of presentations during a hearing test, so a higher value indicates less acute hearing. While hearing loss data in the comparison participants closely matched the average high frequency hearing loss for similar age groups reported for the general population (International Organization for Standardization, 1999), astronauts showed less hearing loss (in the 50 and 60 year-old age groups) than the comparison participants. When compared to a study of Air Force personnel for the years 1975-1976, astronauts also had better hearing sensitivity, suggesting that close vigilance and high motivation in NASA hearing conservation programs among astronauts may have yielded more effective hearing loss prevention.
In the 70 and 80 year-old age groups, astronauts had more hearing loss than the comparison participants. One possible explanation is that hearing conservation programs did not exist or were very primitive prior to 1970. As a result, the current hearing losses among these individuals may have been accelerated by early NIHL, when hearing conservation efforts, now more rigidly enforced, were not effective. Whatever the basis for the audiometric results, it is clear that hearing loss prevention is vital to protecting remaining hearing function.
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