[Scanning electron microscopic study on inner ear barotrauma: in the guinea pig with one eustachian tube occluded]

In order to investigate the mechanism of inner ear barotrauma, guinea pigs, with one eustachian tube occluded, were subjected to compression and decompression between 1 absolute pressure and 2 absolute pressures in a high pressure chamber. The authors divided the animals into three groups according to the speed of compression and decompression. Each group contained 10 guinea pigs. Morphological changes in the cochlear sensory hairs were examined by means of scanning electron microscope. On the occluded side, hair cells were damaged more frequently and more severely by rapid compression than by rapid decompression. There was no difference in the degree of damage produced by slow decompression and rapid decompression. On the control side, slight or moderate damage to hair cells was observed mainly as a result of rapid decompression. These findings led us to hypothesize that, in the setting of normal eustachian tube function, inner ear barotrauma would generally be caused by the relative positive pressure in the middle ear cavity that occurs during decompression. Furthermore, animals deprived of eustachian tube function would not have sufficient endurance for rapid compression and would sustain inner ear barotrauma far more readily, and of far greater severity, with rapid compression than would animals with normal eustachian tube function. The difference may be due to the presence of another pressure transmission pathway to the inner ear. The mechanism of cochlear sensory hair damage due to atmospheric pressure changes is presumed to be distortion of the reticular lamina and cuticular plate caused by the difference in pressure between cortilymph (perilymph) and the subtectorial space (endolymph) resulting in injury to stereocilia.