Structural changes in the rat tympanic membrane following repeated pressure loads

Healthy adult laboratory rats were exposed to alternating negative pressure and atmospheric pressure to replicate the clinical situation found in patients with chronic sniffing habits and chronic middle ear disease. The rats were placed in a box in which the pressure changed at intervals of 30 s between atmospheric pressure and a negative pressure of -3 kPa. This was repeated continuously or periods of 3 and 7 days. At completion of the experimental period, all rats had a normal otomicroscopic status. However, histological studies demonstrated that the pars flaccida was wrinkled and the loose connective tissue contained large fibroblasts with their long axes lying in a disorganized manner. The cells of the keratinizing epithelium were thicker than normal and mitoses were seen. Epithelial crypts filled with keratin were numerous along the epithelium. In the pars tensa, all layers were thicker than normal. These findings demonstrate that repeated pressure loading can create structural changes in the tympanic membrane.