Auditory dysfunction in occupational noise exposed workers.

Occupational noise-induced hearing loss (NIHL) is well known to be an epidemiologically relevant problem. The subjects affected with NIHL show alteration of hearing thresholds as well as a worsening of the cochlear analysis functions and, usually, an impaired speech discrimination in presence of background noise. The study has evaluated the relationships between hearing threshold and equivalent exposure lever per day (Lepd), age and working seniority in a homogeneous sample of occupationally noise exposed workers. Three subgroups were also selected to study the most important cochlear functions as well as nerve and central functions. The first subgroup (Nn) contained normal hearing workers exposed to non-hazardous noise, while the second (Bn) contained workers exposed to high level continuous noise during their work day without clinical evidence of NIHL. The third subgroup (Bd) included subjects affected with the typical 4 kHz notch exposed to the same noise conditions than subgroup Bn. The results show that the hearing impaired subjects have the worst overall cochlear performance; however also the normal hearing workers exposed to hazardous noise have worse performance than subgroup Nn, relatively to high frequency thresholds, frequency resolution, TEOAEs, DPOAEs, stapedial acoustic reflex dynamic parameters. The results suggest that these measures could be used in the monitoring of the NIHL as indicators of subtle alterations of the hearing function.