[Scanning electron microscopic study of inner ear barotrauma: in the guinea pig under hypobaric pressure].

In order to investigate the mechanism of inner ear barotrauma, guinea pigs, with bilateral eustachian tube occlusion, were subjected to decompression and compression between 760 and 460 mmHg in a hypobaric pressure chamber. We divided the guinea pigs into two groups, A and B. Group A showed normal eustachian tubes, and group B showed bilaterally occluded eustachian tubes. Group B animals were divided into three types according to the rates of compression and decompression. After pressure loading, morphological changes in the hair cells of the organ of Corti were studied by means of scanning electron microscopy. There was no damage to hair cells in the setting of normal eustachian tube function, as in group A. On the other hand, mild to severe hair cell damage was observed with rapid decompression in group B. This observation suggests that relative positive pressure in the middle ear cavity is an important factor in inner ear barotrauma. The mechanism of hair cell damage due to inner ear barotrauma is presumed to be distortion of the organ of Corti caused by a difference in pressure between perilymph and endolymph resulting in injury to the stereocilica.