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Texas Neurosciences Institute - Methodist Healthcare - San Antonio, Texas
Ear & Hearing
MECHANISM OF HEARING

The ear is comprised of three portions: an outer ear (external), a middle ear and inner ear. Each part performs an important function in the process of hearing.

The outer (external) ear consists of an auricle and the ear canal. These structures gather the sound and direct it towards the eardrum (tympanic membrane).

The middle ear chamber lies between the external and inner ear. This chamber is connected to the back of the throat (pharynx) by the eustachian tube, which serves as a pressure-equalizing valve. The middle ear consists of an eardrum and three small ear bones (ossicles): malleus (hammer), incus (anvil and stapes (stirrup). These structures transmit sound vibrations to the inner ear. In so doing they act as a transformer, converting sound vibrations in the external ear canal into fluid waves in the inner ear. A disturbance of the eustachian tube, eardrum or the ear bones may result in a conductive hearing impairment. This type of impairment is usually corrected medically or surgically.

The inner ear contains the microscopic hearing nerve endings (hair cells) bathed in fluid. Inner ear fluid waves move the delicate nerve endings, which in turn transmit sound energy to the brain by the hearing nerve where it is interpreted into sound. A disturbance in the inner ear fluids or nerve endings may result in a sensori-neural hearing impairment. Most often, this type of hearing impairment is due to a hair cell loss. This type of impairment is not correctable with surgery.

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, behind the nose). The eustachian tube is approximately 1-½ inches in length. The most narrow portion is that area near the middle ear space.

The eustachian tube functions as a pressure equalizing valve for 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 yawing. 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 retraction (sucking in) of the eardrum (tympani 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 in constantly open the patient may hear himself breathe and ears is voice reverberate in the affected ear. Fullness and a blocked feeling are common sensations experienced by the patient. Abnormal patency of the eustachian tube is annoying but does not produce a hearing impairment.

EUSTACHIAN TUBE PROBLEMS RELATED TO FLYING

Individuals with an eustachian tube problem may experience difficulty equalizing middle ear pressure when flying. When an aircraft ascends, the 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 in the cabin of the aircraft 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 compared to the cabin pressure if the eustachian tube in not functioning properly. Usually, this discomfort is experienced upon descent of the aircraft.

To avoid middle ear problems associated with flying you should not fly if you have an acute upper respiratory problem such as a common cold, allergy attack or sinus infection. Should you have such a problem and must fly, or should have a chronic eustachian tube problem, you may help avoid ear difficulty by observing the following recommendations:

  1. Obtain from your druggist the following items: Sudafed tablets and a plastic squeeze bottle of ¼ percent NeoSynephrine r Afrin nasal spray.
  2. Following the container directions, begin taking Sudafed tablets the day before your air flight. Continue the medication for 24 hours after the flight, if you have experienced any problems equalizing your middle ear pressure.
  3. Following the container directions, use the nasal spray shortly before boarding the aircraft. Should your ears "plug up" upon ascent, hold your nose and swallow while attempting to force air up the back of the throat. This will help suck excess air pressure out of the middle ear.
  4. Forty-five minutes before the aircraft is due to land again use the nasal spray every five minutes for fifteen minutes. Chew gum to stimulate swallowing. Should your ears "plug up" despite this, hold your nose and blow gently toward the back of the throat, while swallowing. This will blow air up the Eustachian tube into the middle ear (Valsalva Maneuver).

None of these recommendations or precautions need to be followed if you have a middle ear eustachian tube (PE tube) in your eardrum (tympanic membrane).

 

   
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