Abstract:
The traditional method of identifying noise-induced hearing loss is through pure tone air conduction audiometry. The measurement of distortion product otoacoustic emissions (DPOAEs), sounde generated within the chochlea in response to aural stimuli, is a relatively new technique which has been proposed as a means to identify preclinical hearing loss. This study was designed to further evaluate the relationship between work-shift noise exposure over a single work-shift and hearing damage as assessed by DPOAEs.
Twenty-two construction workers (44 ears) from 6 different trades participated in the study. The equivalent continuous exposure (Leq) levels measured through full-shift data-logging dosimetry ranged from 75.3 dBA to 92.5 dBA. Ten subjects experienced noise levels above 85 dBA, five of which chose to wear hearing protection. Each subject's hearing ability was evaluated at their construction site pre- and post-shift using audiometry (MAICO MA 41 portable audiometer and TDB 39 earphones) and DPOAE tests (Scout Sport AuDX). Audiometric testing was conducted at the frequencies of 0.5, 1, 2, 3, 4, 6, and 8 kHz, and DPOAEs were measured using DP-Gram. A mobile test vehicle was used to administer the tests; background noise level monitoring indicated the vehicle complied with OSHA audiometric test facility requirements.
Analysis of the data indicated a greater loss in hearing function with higher noise exposure as measured by both audiometry and DPOAEs, with the largest differences observed at 6 kHz. The difference (mean, ±SE) between those exposed above and below 85 dBA at this frequency was 6.5 (± 2.7) and 3.8 (± 1.5) dB for audiometry and DPOAEs, respectively. No difference in hearing outcome was found in a comparison of NIOSH (Leq) and OSHA (Lavg) levels, probably due to high correlation between the two metrics. Analysis of exposure levels for various periods of time prior to post-shift testing showed that the 2 hours of noise exposure immediately prior to testing was the most predictive of changes in DPOAEs, while the full shift (Leq) combined with the logarithmic ratio of (Leq) to (Lavg) was the most predictive of audiometric changes.