Noise-induced low- and high-frequency hearing losses in Finnish conscripts

Thirty-nine otologically healthy military conscripts were examined at the beginning and at the end of their 1-year service. On entry, they all showed normal findings during clinical otolaryngological examinations. The test battery included both conventional (0.25-8 kHz) and high-frequency "electric bone-conduction" (0.5-20 kHz) audiometry (EBC). The median pure-tone right ear thresholds at the end of service were 5 dB worse over the frequency range of 2-8 kHz compared with the thresholds at the beginning of the service. The difference was statistically highly significant (p = 0.00035). The median left ear pure-tone thresholds at frequencies of 0.25, 2, and 8 kHz were 5 dB worse at the end of the service compared to the thresholds at the beginning of the service. However, the difference was not statistically significant (p = 0.23). The median curves for the high-frequency (EBC) thresholds measured after the service showed worse thresholds over the whole frequency range compared to the median curves measured before the service. The greatest difference was seen in the highest frequencies (15-17 kHz) in both ears. The differences were statistically significant in both ears (p = 0.03 in the right ears; p = 0.01 in the left ears) when threshold values over the whole frequency range were analyzed. Since the otolaryngological history of these conscripts was uneventful during their service, the hearing deteriorations were considered to be caused by shooting practice.