Objectives: Otoacoustic emission (OAE) testing is not widespread in Japanese industrial health. This study examined the association between hearing thresholds (HTs) and OAEs among workers exposed to noise in actual workplaces.
Methods: In two metal products manufacturing factories, 34 workers with noise exposure in the workplace (exposure group, mean age 40.6 ± 9.4 years), and 9 workers with no noise exposure (control group, 49.0 ± 14.3 years) were surveyed. The time-weighted average (LAeq) and maximum (LAMAX) of environmental noise monitoring (ENM), and the time-weighted average (LTWA) and sound exposure level (LAE) of personal noise monitoring (PNM) were measured for each subject at the same time. As hearing effect indicators of noise exposure levels, HTs (0.5, 1, 2, 4 and 8 kHz) and distortion product OAEs (DPOAEs) (2, 3 and 4 kHz) were performed before and after 5 days of work. The results of the ENM, PNM, HTs and OAEs were compared between the groups using Student's t test, and their correlations were investigated using Pearson correlation coefficients.
Results: Noise exposure levels of the exposure group were significantly higher than those of the control group. In the exposure group, LAeq, LAMAX, LTWA and LAE were respectively 84.5 ± 4.1 dB(A),89.5 ± 6.3 dB(A), 83.4 ± 4.7 dB(A) and 153.1 ± 15.7 dB(A), and in the control group, they were 53.2 ± 2.6 dB(A), 56.4 ± 2.4 dB(A), 67.8 ± 5.6 dB(A) and 119.5 ± 5.6 dB(A). There was no difference between hearing effect indicators (HTs and OAEs) before and after work in either group. There was no correlation between the noise exposure level (LAeq, LTWA, LTWA and LAE) and HTs or OAEs, but there was a significant correlation between the HTs and OAEs at most of frequencies. The HTs and OAEs of subjects with noise-induced hearing loss (NIHL) were significantly lower than those of subjects without NIHL.
Conclusions: This study revealed there is a significant correlation of the HTs and OAEs before and after 5 days of work. In the future, OAE is expected to be used as a screening test of hearing management of noise-exposed workers in Japan.