Wednesday, June 16, 2010

Function of the Eustachian Tube

The eustachian tube is a narrow channel which connects the middle ear with the nasopharynx (the upper throat area just above the palate, in back of the nose). The Eustachian tube is approximately 1 1/2 inches in length. The narrowest portion is that area near the middle ear space.

The eustachian tube functions as a pressure equalizing valve of the middle ear, which is normally filled with air. Under normal circumstances the eustachian tube opens for a fraction of a second in response to swallowing or yawning. In so doing it allows air into the middle ear to replace air that has been absorbed by the middle ear lining (mucous membrane) or to equalize pressure changes occurring with altitude changes. Anything that interferes with this periodic opening and closing of the eustachian tube may result in a hearing impairment or other ear symptoms.

Obstruction or blockage of the eustachian tube results in a negative middle ear pressure, with restraction (sucking in) of the eardrum (tympanic membrane). In an adult this is usually accompanied by some discomfort, such as a fullness or pressure feeling, and may result in a mild hearing impairment and head noise (tinnitus). In children there may be no symptoms. If the obstruction is prolonged, the fluid may be sucked in from the mucous membrane in the middle ear creating a condition called serous otitis media (fluid in the middle ear). This occurs frequently in children in connection with an upper respiratory infection or allergies and accounts for the hearing impairment associated with this condition.

On occasion just the opposite from blockage occurs; the tube remains open for a prolonged period. This is called abnormal patency of the eustachian tube (patalous eustachian tube). This is less common than serous otitis media and occurs primarily in adults. Because the tube is constantly open the patient may hear himself breathe and hears his voice reverberate in the affected ear. Fullness and a blocked feeling are not uncommon sensations experienced by the patient. Abnormal patency of the eustachian tube is annoying but does not produce a hearing impairment.

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