An air-containing middle ear is necessary for normal hearing, both because it allows free vibration of the eardrum and ossicles so that sound pressure can be transmitted to the inner ear fluid and because it affords protection from sound to the round window. This air-containing space is maintained by the Eustachian tube, which opens intermittently to equalize the intratympanic air pressure with the pressure in the external auditory canal. It also removes secretion and epithelial debris from the middle ear by ciliary motion and gravity. Pathology of the Eustachian Tube in Chronic Otitis Media Acute otitis media causes edema of the membrane lining, the Eustachian tube, and the middle ear. This edema may be maintained as long as there is infection in the ear spaces, and it produces the simplest form of Eustachian tube blockage. In this type of case, it may be possible to inflate the tube by the