Search

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.

Recent investigations have demonstrated that in animal models repeated exposures to mid-intensity noise induce a progressive reduction of the temporary threshold shift (TTS) following the exposures. This phenomenon is named "conditioning" and it is actually able to reduce the permanent threshold shift (PTS) following exposure to high intensity noise; this finding is named "toughening". In the present work the fundamental steps of the research concerning the toughening are reviewed and the biological mechanisms supposed to be underlying this phenomenon discussed. The few preliminary results of the studies on humans are also reported.

Estimates for the prevalence of self-reported hearing disability and measured hearing impairment as a function of age in the adult population of Italy are reported. The study was conducted in Bari, Florence, Milan, Padua, Palermo with questionnaire and audiological assessment; neither stage showed any gross bias arising from the particular cities chosen. The results have demonstrated that: 22% of subjects think their hearing abnormal, 24.4% report some difficulty understanding speech, 14.5% experienced prolonged spontaneous tinnitus and 17% have a > or = 25 dB HL bilateral hearing impairment; hearing problems increase progressively with age and show no significant differences between men and women; the occupational groups most at risk as far as hearing impairments are concerned are manual workers and workers exposed to occupational noise; the systemic disorders most significantly connected to hearing problems are dyslipidosis, diabetes, hypertension, cardiovascular diseases, liver diseases and cervical arthrosis; among every day habits, the consumption of alcohol seems the only element of risk, above all for tinnitus.