INNER-EAR DAMAGE IN GUINEA-PIGS EXPOSED TO STABLE AND IMPULSE NOISE

Objective To investigate the inner ear damage after exposure to stable noise, impulse noise and stable plus impulse noise in guinea pigs. Me thods 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 s econds. (3) stable plus impulse noise group: exposed to the same stabl e noise as that in the first group, then after a 2-hour rest, the anim als were followed with impulse noise exposures as that in the second g roup. After those exposure, each of the 3 groups was further divided i nto 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 pote ntial responses to click and tone burst stimulation sound were examine d. The surface preparation and celloidine embedded serial section of t he cochlea were observed under a light microscope. Results Both the st able and impulse noise could increase the hearing threshold and damage the inner ear hair cells. The damage in the first group was relativel y slight, whereas in group 3 the damage was more severe than that in t he other 2 groups. Conclusion For seamen who are working in heavy nois e environment, corresponding measures should be taken to protect their ears from noise which induces hearing loss.