Chronic effects of phasic middle ear pressure changes.

In an attempt to better define the mechanisms of barotrauma, middle and inner ear pathology was studied in guinea pigs three weeks following exposure to a brief, sudden middle ear pressure change. Findings included tympanic membrane perforations (particularly dependent upon high negative pressure exposures), vascular hemorrhage (primarily dependent upon high positive pressure exposures), serosanguineous effusions (predominantly dependent upon infection) and serous effusion (dependent upon negative pressure exposure). Round window perforations were common in high pressure animals with infection. Other inner ear membrane changes were infrequent or minimal. Lymphatic hemorrhage was observed as a function of exposure. The clinical implications of these findings and possible mechanisms underlying these changes are discussed in terms of our previously reported study of the immediate effects of such pressure change.