Eustachian Tube Function

The eustachian tube, or auditory tube, connects the middle ear to the nasopharynx which is the upper part of the throat behind the nose. The tube is situated just above the floor of the middle ear and has triangular to oval shaped opening at both ends. Bone, cartilage, and fibrous tissue makes up the eustachian tube. Within the tube itself, there are also different surfaces, the upper portion of the tube is smooth, while the bottom portion of the tube contains cilia, or hair-like structures.

Eustacian tube length in children is approximately 37.5 to 38 mm in childhood and about 42.5 to 42.9 mm in adults.

The angle of the tube in children is approximately 20 degrees, although it has been measured as little as 10 degrees in young children. This differs in adults, where the angle is more significant depending on how it is measured. It has been measured at 34–36 degrees with the horizontal plane but with reference to the sagittal plane is estimated to be approximately 42 degrees. The shallow angle of the Eustachian tube in children is considered to be one of the factors that increases the risk of children developing middle ear dysfunction, ear infections and fluid in their ears.

Efficiency of muscle also differs in children and adults. There are six muscles that contribute to the opening and closing of the eustachian tube: tensor tympani, salpingopharyngeus; tensor veli palatini; levator veli palatini; lateral and medial pterygoids. In children, these muscles are more passive, while in adults, they have a more active involvement. This difference is also thought to contribute to increased risk for children developing middle ear dysfunction.

The eustachian tube is most commonly known for its role in equalizing pressure within the middle ear. This is indeed an important role, however the eustachian tube serves the following three roles. These include:

• Pressure equalization of the middle ear
• Draining the middle ear space
• Protecting the middle ear from bacteria or viruses

On average the eustachian tube opens once or twice every hour. When opened, it normally only remains open for about 0.3 to 0.5 seconds. The eustachian tube however opens more frequently and for longer duration when yawning.

Atmospheric pressure changes as you change altitude and as the weather changes. When the atmospheric pressure changes, the ear drum changes shape due to an unequalized pressure in the middle ear.

Without equalizing the pressure, the ear drum cannot respond to sound in the same way and your hearing is affected. If the pressure in the middle ear is not equalized and greater pressure is applied, you can experience pain and in extreme instances a ruptured ear drum can occur. When your ear does equalize you may experience a "popping" sensation.

In order to maintain proper functioning of the middle ear, the space needs to be free of fluid and other debris. Tiny hair-like structures, known as cilia, actively move material toward the opening of the eustachian tube. This process is not gravity dependent and will occur normally unless there is a problem with the mechanism; like in the condition primary ciliary dyskinesia.

Once in the middle ear, the bottom of the tube have mucus and cilia that beat (or move back and forth in a wave like motion); moving the material down the eustachian tube to the back of the throat.

Several things can affect the normal function of this process by changing the viscosity, or thickness of the mucus in the eustachian tube. Examples of disorders that can change the thickness of the mucus includes: cystic fibrosis, otitis media, and sinusitis. Bacterial and viral infections can also affect the normal function of this process and may take up to one month after recovering for normal function of cilia to return.

Other obstacles can also occlude or partially block the eustachian tube opening in the back of the throat. Enlarged adenoids and adenoids in small children can be a cause of this blockage. If necessary an adenoidectomy can be performed to free up space around the eustachian tube.

Under normal circumstances, the opening of the eustachian tube in the back of the throat is closed. This serves three protective functions:

• Barrier to bacteria and viruses from going up the eustachian tube
• Prohibits sound from vocalization from traveling into the middle ear space
• Helps dissipate sound pressure in the middle ear as a result of really loud sounds

This protection is interrupted by disorders that cause the eustachian tube opening in the back of the throat to remain open. Patulous eustachian tube is an example of this and is widely recognized by it's tell-tale sign of autophony, or unusually loud hearing of one's own voice or breathing.

When you are changing altitude, it is common to experience plugged ears. While initially this feeling is only an annoyance, without proper equalization, pain may develop as you continue to change altitude. In order to relieve the sensation or pain, you need to open the eustachian tube. Here are some methods to try:

• Yawning
• Sneezing
• Chewing gum
• Toynbee maneuver - swallowing while squeezing your nose shut
• Shaking your head back and forth
• Swallowing