The aims of this study were to evaluate the influence of age and exposure to noise in determining the evolution of hearing loss after noise-induced hearing loss has been already established and to define the further evolution of presbycusis. This is a cross-sectional study based on the evaluation of pure-tone audiometry threshold on 568 subjects affected by noise-induced hearing loss and exposed to noise for at least 10 years; noise exposure at testing was 85-90 dB Leqd(A). The further evolution of hearing loss was found to be more related to age than to noise exposure and was significantly less than expected for presbycusis. In conclusion our data support the hypothesis that once NIHL has manifested, it tends to worsen slightly with continued noise exposure and that progressive hearing loss is chiefly due to aging. However, in individuals with NIHL, age-related hearing loss is significantly less at frequencies damaged by noise than in non-noise-exposed individuals.

To assess the reliability of Blackman windowed tone burst auditory brainstem response (ABR) as a predictor of hearing threshold at low frequencies. Fifty-six subjects were divided in to three groups (normal hearing, conductive hearing loss, sensorineural hearing loss) after pure tone audiometry (PTA) testing. Then they underwent tone burst ABR using Blackman windowed stimuli at 0.5 kHz and 1 kHz. Results were compared with PTA threshold. Mean threshold differences between PTA and ABR ranged between 11 dB at 0.5 kHz and 14 dB at 1 kHz. ABR threshold was worse than PTA in each but 2 cases. Mean discrepancy between the two thresholds was about 20 dB in normal hearing, reducing in presence of hearing loss, without any differences in conductive and sensorineural cases. Tone burst ABR is a good predictor of hearing threshold at low frequencies, in case of suspected hearing loss. Further studies are recommended to evaluate an ipsilateral masking such as notched noise to ensure greater frequency specificity.

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