Left and right Eustachian tubes connect the corresponding left and right middle ears (tympanic cavities) to the back of the nose and throat, and function to allow the equalization of pressure in the middle ear air cavity with the outside (ambient) air pressure. The membrane-lined tubes, also called the auditory tubes, serve to drain secretions from the middle ear to the nasopharynx region. The Eustachian tubes are normally closed to prevent a back fill of fluid and particulate debris from the mouth and nose. Muscles in the throat and palate area control the opening and closing of the tubes. When subjected to pressure the tubes may collapse or fail to open unless pressurized. Some disease processes, especially chronic ear infections, may obstruct the tubes and result in a painful difference in pressure between the middle ear and the pressure found in the nose and throat.
Chronic ear infections usually result from Eustachian tubes that fail to close properly or that remain open. Eustachian tubes always open are termed patent or patulous Eustachian tubes. Obstructions of a Eustachian tube may result in an uncomfortable or painful feeling of pressure in the middle ear. Such sensations are often accompanied by popping and clicking noises associated with swallowing. The pos and clicks result form tiny expulsions of pressurized air as the muscles surrounding the Eustachian tubes exert forces that may briefly open the tubes.
Patent Eustachian tubes also allow secretions from the nose and throat to reach the middle ear and this may result in severe chronic infections of the middle ear. A failure to equalize middle ear pressure via the Eustachian tubes may also result in the creation of a partial vacuum in the middle ear that actually draws secretions into the middle ear (serous otitis media).
Pressure variations in the middle ear may also impair hearing, especially a loss of hearing acuity that results in sounds being muffled or otherwise diminished or attenuated. Proper function of the Eustachian tube is required to normalize pressure on the tympanic membrane. Middle ear problems can also result in poor balance.
Inflammations and secretions associated with colds, allergies, and sinus or respiratory infections may also block one or both of the Eustachian tubes. Tumors or other physical obstructions may also impair tube function and create both painful pressure and a ringing sensation in the ears (tinnitus).
Because the Eustachian tubes are located close to the adenoids, the removal of the adenoids, especially in children with smaller diameter tubes more easily obstructed, may allow the tubes to function normally. Temporary tubal inserts are more commonly used to allow drainage of the middle ear.
Proper functioning Eustachian tubes are important to divers and aviators who experience often rapid and significant changes in outside pressure. Although commercial airplanes are usually pressurized, there are significant enough changes in pressure during climbs and descents to cause pain in individuals suffering even slight tube blockage. Some people attempt to assure and improve Eustachian tube function during flights by chewing gum during airline flights. The combined muscle movements associated with chewing and swallowing (saliva) work to frequently open and close the Eustachian tubes and permit middle ear pressure equalization.
The external carotid arteries supply oxygenated blood to the Eustachian tubes via their respective pharyngeal branches. The maxillary artery derived middle meningeal artery and pterygoid canal artery also supply blood to the Eustachian tubes. Blood drains form the tubes via the pterygoid venous plexus. The tubes are innervated (supplied with nerves) from a tympanic plexus derived from the cervical sympathetic, glossopharyngeal, and facial nerves.
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