The interaction of whole body vibration and noise on the cochlea

The structural and functional effects of separate and combined exposure to noise and whole body vibration were studied in 40 guinea pigs. The animals were divided into control (N=10) and study groups (N=30). The study group was subdivided into three sub-groups: noise (N), vibration (V) and noise and vibration (N&V). Apart from the control group, the other sub-groups were exposed to the noxious agent for 6 h per day for 4 weeks. After these 4 weeks, distortion product otoacoustic emission (DPOAE) was measured, then half the number of the animals was sacrificed. The other half were left to recover for another 4 weeks, at the end of which DOPAE was measured. Then all the animals were sacrificed; the cochlea was studied by light and transmission electron microscopy. The results showed a clear and evident more damaging effect of combined exposure to noise and vibration on cochlea of guinea pigs than exposure to noise only. Moreover, the ability to recover was less in the case of combined exposure. The exposure to vibration only led to enhancement of both DPOAE amplitudes and signal to noise ratios with more damage to the inner hair cells than the outer hair cells. On the contrary, the effects of exposure to noise only led to more injury to outer hair cells than the inner ones, the combined exposure had an equal damaging effects on both outer and inner hair cells.