Experimental aural barotrauma. Electrophysiological and morphological findings.

The electrophysiological findings show a time and pressure related decrease in function of the CM and the N1 potentials. Sudden changes were correlated with tympanic membrane perforations. Some of the decreased function is accounted for by middle ear effusion and hemorrhages, reducing mechanically the transmission of sound energy through the middle ear. This was evidenced by an improvement of function when the fluids were removed. Remaining decreases in function were interpreted as a result of influences on the inner ear function or of undisclosed middle ear changes. No differences were noted in cochlear function between animals subjected to sustained or intermittent middle ear pressures. Neither were any morphological differences noted between these two groups in the middle or inner ear. The morphological middle ear findings correlated well with previous clinically and experimentally induced changes with increased/decreased middle ear pressure. The cochlear findings include the interesting observation of an intact round window membrane, a clear endolymph, and a normal Organ of Corti in all cases. Positive findings were a high frequency of hemorrhage, most commonly demonstrated in the scala tympani of the basal turn close to the round window. The origin of the hemorrhages could not be demonstrated with the present investigation. The hemorrhages often appeared to be related to the cochlear aqueduct. The occurrence of hemorrhage was clearly related to increased negative pressure, and the non-existence of hemorrhage was always related to either tympanic membrane perforations or low applied pressure. Further frequent findings were distention, collapse, and rupture of the inner ear membranes which must be interpreted with great circumspection due to the method used. Likewise, some of the pathological cochlear findings may be due to pathological conditions which are not necessarily related to induced middle ear pressure.