Objective: To investigate the inner ear damage after exposure to stable noise, impulse noise and stable plus impulse noise in guinea pigs.
Methods: Ninety-six healthy guinea pigs were divided into 3 equal groups. (1) Stable noise group: exposed to 110 dBA stable noise for 3 days, 4 hours per day. (2) Impulse noise group: exposed to 165 dBA simulated cannon fire impulse noise 10 times successively at an interval of 10 seconds. (3) stable plus impulse noise group: exposed to the same stable noise as that in the first group, then after a 2-hour rest, the animals were followed with impulse noise exposures as that in the second group. After those exposure, each of the 3 groups was further divided into 4 subgroups according to the time after the noise exposure, namely, the right after, 7 d, 14 d and 30 d groups. The evoked cortical potential responses to click and tone burst stimulation sound were examined. The surface preparation and celloidine embedded serial section of the cochlea were observed under a light microscope.
Results: Both the stable and impulse noise could increase the hearing threshold and damage the inner ear hair cells. The damage in the first group was relatively slight, whereas in group 3 the damage was more severe than that in the other 2 groups.
Conclusion: For seamen who are working in heavy noise environment, corresponding measures should be taken to protect their ears from noise which induces hearing loss.