A tympanometry test assesses the health and function of the middle ear. This non-invasive procedure measures eardrum movement, helping diagnose hearing issues. It provides objective information about the eardrum and the small bones behind it.
What Tympanometry Measures
Tympanometry measures how the eardrum and middle ear system respond to changes in air pressure. It assesses acoustic immittance, which is the resistance or compliance of the middle ear to sound energy. The test determines eardrum mobility, middle ear air pressure, and ear canal volume.
The test works by sending a low-frequency tone, typically 226 Hz for adults, into the ear canal while varying the air pressure. A microphone within the probe measures the sound waves reflected back from the eardrum. If the eardrum is moving freely, more sound energy is absorbed into the middle ear. If the eardrum’s movement is restricted, more sound is reflected, indicating a potential problem. The tympanometer then plots these measurements on a graph called a tympanogram, showing compliance (eardrum movement) against pressure.
How a Tympanometry Test is Conducted
Before the tympanometry test, a healthcare provider performs an otoscopy, a visual inspection of the ear canal and eardrum using a lighted scope. This ensures the ear canal is clear of obstructions, like earwax, and that the eardrum is intact. Next, a small, soft-tipped probe is gently placed into the ear canal, creating an airtight seal.
Once the seal is established, the tympanometer automatically changes the air pressure within the sealed ear canal. A low-pitched tone is emitted into the ear during this process. You might feel a slight pressure change, similar to the sensation during an airplane’s ascent or descent. Remain still, avoid talking, swallowing, or laughing during the brief test to ensure accurate results. The entire procedure takes only a few seconds per ear and is painless.
Interpreting Tympanometry Results
The results of a tympanometry test are displayed as a graph known as a tympanogram, which plots middle ear compliance against air pressure. Different shapes of this graph indicate various middle ear conditions. The most common classifications are Type A, Type B, and Type C.
A Type A tympanogram represents normal middle ear function. This graph shows a distinct, mountain-shaped peak around 0 daPa (decapascals), which is atmospheric pressure. This indicates that the eardrum moves normally and that the pressure in the middle ear is balanced with the external ear canal pressure. Normal results suggest there is no fluid behind the eardrum and the ossicles, the small bones in the middle ear, are moving as expected.
A Type B tympanogram appears as a flat line with little to no peak. This shape suggests that the eardrum is not moving or has very limited movement in response to pressure changes. A common cause for a Type B tympanogram is the presence of fluid in the middle ear, often associated with middle ear infections. If the ear canal volume is unusually large with a flat line, it can indicate a perforated eardrum or a patent tympanostomy tube (ear tube), as the air pressure is no longer confined to the ear canal but extends into the middle ear space.
A Type C tympanogram features a peak shifted to the negative pressure side of the graph, typically below -100 daPa. This indicates negative pressure within the middle ear. This suggests Eustachian tube dysfunction, where the tube connecting the middle ear to the throat is not equalizing pressure properly. This result can occur during or after a cold, sinus congestion, or an ear infection.