Tympanometry is a test used to evaluate hearing and detect disorders of the middle ear, the space behind the eardrum (tympanic membrane). The middle ear is frequently the site of ear infections in children.

Tympanometry involves the use of a small probe that resembles an ear plug. The probe has four functions:

• Creates an airtight seal around the ear
• Changes the air pressure inside the ear
• Produces a pure, continuous tone of sound
• Records the middle ear’s response to the pressure changes and sounds it creates

During the test, a gentle stream of air is pumped through the probe and into the ear, causing the pressure to increase and decrease at intervals to see how well the eardrum (tympanic membrane) responds. As pressure changes are introduced, the patient hears sounds resulting from the air pressure pushing on the eardrum. The eardrum transmits these vibrations to the bones of the middle ear. The probe inside the ear measures how much of the sound passes through the middle ear and how much is reflected back. This information is transmitted to a tympanometer, which then creates an information readout known as a tympanogram.

Most of the time, the eardrum will respond well to the test. A good reading on a tympanogram looks like an inverted “V” with the center point lining up directly over the “zero” mark on a chart. This indicates that the air pressure in the middle ear is identical to the pressure in the room.

An eardrum that does not move properly will result in a tympanogram that is either flattened (indicating that little sound is being reflected back to the tympanometer) or that shows the “V” shifted to the left (indicating that there is less pressure behind the eardrum than there is in the room). An abnormal reading can indicate a number of disorders, including:

• Ear infection (e.g., otitis media). Commonly found in children, it is triggered by a cold or other respiratory infection and produces symptoms of sharp pain and fever. Severe nasal allergies (e.g., allergic rhinitis) can cause recurrent ear infections.
  
  
• Blocked eustachian tube (connects middle ear space to back of nose and throat). Upper respiratory infections can cause inflammation and blockage of this tube. Severe nasal allergies produce mucus that can flow back into the eustachian tube, creating a blockage.
  
  
• Fluid in the middle ear space (otitis media with effusion). Often the result of an ear infection, cold or flu, it prevents the eardrum and middle-ear bones from moving properly.
  
  
• Perforated eardrum (hole in the eardrum). It can be caused by trauma or a sudden pressure increase, usually from an acute infection.
  
  
• Disruption in chain of three bones (ossicles) that propel sounds through the middle ear. This is often caused by a buildup of fluid that prevents the bones from moving properly. Over time, secretion due to nasal allergies can build up and stick to the ossicles, affecting a person’s ability to hear. This condition is known as chronic secretory otitis media, or “glue ear.”
  
  
• Stiffness in the eardrum or the bones of the middle ear. It may be caused by otosclerosis, a hereditary disorder that causes a bone in the ear to grow excessively.

Tympanometry also measures shifts in the stapedius muscle, which normally contracts in response to loud noises. This action – known as the acoustic reflex – reduces sound transmission and protects the inner ear. Neural hearing loss (which results from a problem with the auditory nerve) is suspected if the stapedius muscle does not properly contract. It often is the result of a benign tumor in the middle ear.

The tympanometry test may be performed after a pneumatic otoscopy. Pneumatic otoscopy is a test that allows a healthcare provider to visually examine a patient’s eardrum to see how well it moves in response to pressure changes inside the ear. Using these tests together improves the accuracy of the patient’s diagnosis.

The tympanometry test should be a part of hearing evaluation for all children, although the test may not be accurate in infants under seven months old. This is due to the fact that the ear canals of infants younger than seven months are highly compliant. In addition, children who are crying or uncooperative during the test may make it difficult or impossible to obtain accurate test results.