Extended high-frequency audiometry and noise induced hearing loss in cement workers

Background It has been suggested that extended high-frequency audiometry (EHEA) might be more sensitive than conventional audiometry in detecting early signs of hearing impairment. However, this technique has not been adequately tested in an occupational environment. We therefore investigated the usefulness of this method in noise-exposed workers. Methods We compared conventional frequency audiometry (0.25-8 kHz) and EHEA (9-18 kHz) in 184 noise-exposed and 98 non-noise-exposed workers. Results Both methods showed significantly higher threshold levels (P < 0.05) in noise-exposed workers for most of the tested frequencies; however, the differences were more marked for EHEA, especially in young exposed workers. Significant differences in the EHF range were detected also in the subgroup of noise-exposed workers with normal findings at conventional audiometry. Stepwise regression analysis showed that in 21 - to 40-year-old workers the noise effect was largely predominant at both conventional audiometry and EHFA, whereas in older subjects the noise effect was predominant up to 6 kHz frequency, the effect of age being significantly greater at higher frequencies. Conclusions These data indicate that EHEA is more sensitive than conventional audiometry in detecting noise induced hearing loss. However, heating loss in the EHF range seems an age-dependent phenomenon with progression into the lower speech range frequencies with increasing age. These changes seem to be accentuated in the early years by noise exposure, suggesting that EHFA could represent a useful preventive measure in young exposed workers.