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 sh ow alteration of hearing thresholds as well as a worsening of the coch lear analysis functions and, usually, an impaired speech discriminatio n in presence of background noise. The study has evaluated the relatio nships between hearing threshold and equivalent exposure lever per day (Lepd), age and working seniority in a homogeneous sample of occupati onally noise exposed workers. Three subgroups were also selected to st udy the most important cochlear functions as well as nerve and central functions. The first subgroup (Nn) contained normal hearing workers e xposed 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 (Ed) included subjects a ffected with the typical 4 kHz notch exposed to the same noise conditi ons than subgroup Bn. The results show that the hearing impaired subje cts have the worst overall cochlear performance; however also the norm al hearing workers exposed to hazardous noise have worse performance t han subgroup Nn, relatively to high frequency thresholds, frequency re solution, TEOAEs, DPOAEs, stapedial acoustic reflex dynamic parameters . The results suggest that these measures could be used in the monitor ing of the NIHL as indicators of subtle alterations of the hearing fun ction.