Tympanometry is a swift, objective, and non-invasive diagnostic procedure used by healthcare professionals to assess the functional status of the middle ear system. This test checks the health and mechanics of the eardrum and the space directly behind it. It provides quantitative information about how effectively sound energy is transmitted through the middle ear. The primary purpose of tympanometry is to measure the mobility of the tympanic membrane (eardrum) in response to controlled changes in air pressure within the ear canal. Evaluating this movement helps identify potential causes of hearing loss or discomfort originating in the middle ear.
The Mechanics of Middle Ear Assessment
The measurement process involves a device called a tympanometer, which uses a probe tip inserted into the ear canal to create an airtight seal. This probe contains three distinct ports: one for a miniature speaker, one for a microphone, and one connected to an air pressure pump. The speaker emits a continuous, low-frequency sound tone, typically 226 Hertz in adults, toward the eardrum.
The air pump systematically varies the air pressure within the sealed ear canal, sweeping from positive pressure to negative pressure. As this pressure changes, the mobility of the eardrum is affected, causing it to move either inward or outward. The microphone measures the amount of sound energy that is reflected back from the eardrum, which directly relates to its stiffness or compliance.
The two primary physical properties being assessed are the air pressure within the middle ear cavity and the mobility of the eardrum and the tiny bones of hearing, known as the ossicles. Maximum compliance is recorded when the pressure in the ear canal matches the pressure in the middle ear space, allowing the eardrum to vibrate most efficiently. The resulting data is then plotted onto a graph called a tympanogram, which visualizes the relationship between the applied pressure and the eardrum’s movement.
Diagnosing Fluid and Pressure Conditions
Tympanometry is most commonly used to identify the presence of fluid in the middle ear, a condition often associated with Otitis Media with effusion. When fluid fills the middle ear space, it significantly reduces the eardrum’s ability to vibrate, resulting in a stiffened system. This lack of mobility is a strong indicator of effusion, helping to differentiate it from other types of hearing loss.
The test is also effective at assessing the function of the Eustachian tube, the small canal connecting the middle ear to the back of the nose and throat. This tube’s main job is to equalize the pressure between the middle ear and the outer environment. When the Eustachian tube is blocked or dysfunctional, the air inside the middle ear is absorbed, creating negative pressure that pulls the eardrum inward.
This negative pressure can be precisely measured by the tympanometer, providing an objective sign of poor tube function, which is a frequent cause of ear discomfort and mild hearing reduction. Additionally, the test can help detect a perforation (hole) in the eardrum, or an issue with the ossicular chain, such as fixation or discontinuity. In the case of a perforation, the tympanometer measures an abnormally large ear canal volume because it includes the volume of both the ear canal and the middle ear space.
Understanding the Results: Interpreting Tympanogram Types
The tympanogram plots the measured compliance (eardrum mobility) on the vertical axis against the applied air pressure (measured in decaPascals, or daPa) on the horizontal axis. The shape and location of the resulting curve provide specific diagnostic information, which is categorized into different types, most commonly using the Jerger system (Types A, B, and C).
A Type A tympanogram is considered normal, characterized by a sharp, inverted V-shape peak that falls within the normal pressure range, typically between -100 and +100 daPa. This peak indicates that the eardrum and middle ear system are moving with normal compliance and balanced pressure.
A Type B tympanogram is represented by a flat line with no discernible peak, signifying that the eardrum is stiff and immobile. This flat tracing most often points to fluid behind the eardrum or an obstruction like earwax completely blocking the ear canal.
The Type C tympanogram features a peak shifted significantly into the negative pressure range, usually below -100 daPa. This displacement indicates that the middle ear pressure is substantially lower than the pressure in the ear canal. This result is the classic sign of Eustachian tube dysfunction and often appears before or after a middle ear infection.