FUNCTION OF THE EUSTACHIAN TUBE
The middle ear chamber lies between the external and inner ear. This chamber is connected to the back of the throat by the eustachian tube. The eustachian tube is a narrow, one and a half inch long channel connecting the middle ear with the nasopharynx, the upper throat area just above the palate, in back of the nose.
The eustachian tube functions as a pressure equalizing valve for the middle ear which is normally filled with air. When functioning properly, the eustachian tube opens for a fraction of a second periodically (about once every three minutes) 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 differences occurring with altitude changes. Anything that interferes with this periodic opening and closing of the eustachian tube may result in conductive hearing impairment or other ear symptoms.
Obstruction or blockage of the eustachian tube results in a negative middle ear pressure, with retraction (sucking in) of the eardrum membrane. In the adult, this is usually accompanied by some ear discomfort, a fullness or pressure feeling and may result in a mild conductive hearing impairment and head noise (tinnitus). There may be no symptoms in children. If the obstruction is prolonged, fluid may be drawn from the mucous membrane of the middle ear creating a condition we call serous otitis media . This occurs frequently in children in connection with an upper respiratory infection and accounts for the conductive hearing impairment associated with this condition.
Occasionally pain or middle ear fluid develops when landing in an aircraft. This is due to failure of the eustachian tube to properly equalize the middle ear air pressure, and the condition is called aerotitis. It is temporary and often can be avoided by taking precautions.
On occasion, just the opposite from blockage occurs: the tube remains open for prolonged periods. This is called abnormal patency of the eustachian tube or a patulous Eustachian tube.. This condition is less common than serous otitis media and occurs primarily in adults. Because the tube is constantly open, the patient may sense his/her own breathing and voice reverberate in the involved ear. Fullness and a blocked feeling are not uncommon. Abnormal patency of the eustachian tube may be annoying but does not produce hearing impairment.
Individuals with a eustachian tube problem may experience difficulty equalizing middle ear pressure when flying.
When an aircraft ascends, atmospheric pressure decreases, resulting in a relative increase in the middle ear air pressure. When the aircraft descends, just the opposite occurs: atmospheric pressure increases, and there is a relative decrease in the middle ear pressure. Either situation may result in discomfort in the ear due to abnormal middle ear pressure if the eustachian tube is not functioning properly. Usually, this discomfort is experienced upon aircraft descent.
Serous otitis media is the term we use to describe a collection of fluid in the middle ear. This may be acute or chronic.
Acute serous otitis media is usually the result of blockage of the eustachian tube from an upper respiratory infection or an attack of nasal allergy. In the presence of bacteria, this fluid may become infected, leading to an acute suppurative otitis media (infected or abscessed middle ear). When infection does not develop, the fluid remains until the eustachian tube again begins to function normally, at which time the fluid is absorbed or drains down the tube into the throat.
Chronic serous otitis media may result from long-standing eustachian tube blockage, or from thickening of the fluids so that it cannot be absorbed or drained down the tube. This chronic condition is usually associated with hearing impairment. There may be recurrent ear pain, especially when the individual catches a cold. Fortunately, serous otitis media may persist for many years without producing any permanent damage to the middle ear mechanism. The presence of fluid in the middle ear, however, makes it very susceptible to recurrent acute infections. These recurrent infections may result in middle ear damage.
Serous otitis media may result from any condition that interferes with the periodic opening and closing of the eustachian tube. The causes may be congenital (present at birth), may be due to infection or allergy, or may be due to blockage of the tube by adenoids.
The size and shape of the eustachian tube is different in children than in adults. This accounts for the fact that serous otitis media is more common in very young children. Some children inherit small eustachian tubes from their parents; this accounts in part for the familial tendency to middle ear infection. As the child matures, the eustachian tube usually assumes a more adult shape.
Serous otitis media is more common in the child with a cleft palate. This is due to the fact that the muscles that move the palate also open the eustachian tube. These muscles are deficient or abnormal in the cleft palate child.
The lining membrane (mucous membrane) of the middle ear and eustachian tube is connected with, and is the same as, the membrane of the nose, sinuses and throat. Infection of these areas results in mucous membrane swelling which in turn may result in eustachian tube obstruction.
Allergic reactions in the nose and throat result in mucous membrane swelling, and this swelling may also affect the eustachian tube. This reaction may be acute, as in a hay fever type reaction, or may be chronic, as in many varieties of “chronic sinusitis”.
The adenoids are located in the nasopharynx, in the area around and between the eustachian tube openings. When enlarged, the adenoids may block the eustachian tube opening.
In the presence of an upper respiratory infection, such as a cold, tonsillitis or sinusitis, fluid in the middle ear may become infected. This results in what is commonly called an abscessed ear or an infected ear.
This infected fluid (pus) in the middle ear may cause severe pain. If examination reveals that there is considerable bulging of the ear drum due to increased middle ear pressure, a myringotomy (incision of the eardrum membrane) may be necessary to drain the abscess and the relieve the pain and pressure. In most cases, antibiotic treatment will suffice.
Resolution of the acute infection occasionally leaves the patient with uninfected fluid in the middle ear. This is called chronic serous otitis media and this condition may persist for several weeks.
Chronic serous mastoiditis and idiopathic hemotympanum are uncommon conditions that have the same symptoms as chronic serous otitis media. They differ in that the middle ear fluid continues to form, either draining out the ventilation tube or blocking it completely so that the tube dislodges shortly after surgery. This persistent fluid formation is due to changes in the mucous membrane of the middle ear and mastoid.
Abnormal patency of the eustachian tube is a condition occurring primarily in adults, in which the eustachian tube remains “open” for prolonged periods. This abnormality may produce many distressing symptoms: ear fullness and blockage, a hollow feeling, hearing one’s own breathing and voice reverberation. It does not produce hearing impairment.
The exact cause of an abnormal patent eustachian tube is often difficult to determine. At times it develops following weight loss . It may develop during pregnancy or while taking oral contraceptives or other hormones.