Experimental studies of vibratory trauma of Corti's organ. II. Scanning electron microscopy.
In the first part of this study, the authors presented the results of cochlear microphonics measurements in guinea pigs subjected to long-term whole-body vibration. In animals undergoing vibration over 30, 90, and 180 days, a statistically significant lowering of voltage over the range up to 2 kHz was seen. In accordance with cochlear-frequency position, this pointed to possible formation of sensory epithelium damages in the fourth and third turning. In the present study an attempt was made to verify electrophysiological measurements with a scanning electron microscope. In all, 80 cochleae were examined, 20 in each group of animals: one control and three experimental groups. The healthy animals showed a correct picture of the sensory epithelium in each case, whereas its damage was ascertained in all the study groups. The damage advanced with a longer duration of the experiment and was most often seen in the outer hair cell region of the apex, where it gradually spread towards the base of the cochlea. The damage of cells decreased from the circumference to the modiolus, and the inner hair cells showed considerably greater resistance to vibration. The results of the study demonstrate the harmful effect of mechanical vibration on the inner ear. According to the observed pattern of damage, one can expect an increasing hearing impairment in the low and medium frequency range in persons exposed to whole-body vibration.