Tympanometry is a specialized, objective test used by healthcare professionals to assess the condition and function of the middle ear and the mobility of the tympanic membrane (eardrum). Unlike a standard hearing test, this procedure does not measure hearing sensitivity or the ability to perceive sound. Instead, it measures how sound energy is transmitted through the middle ear system. This non-invasive evaluation helps identify and diagnose middle ear problems, such as fluid accumulation or pressure imbalances, that may contribute to hearing difficulty.
How Tympanometry Measures Middle Ear Function
The test works by using a small instrument called a tympanometer, which mechanically evaluates the health of the eardrum and the tiny bones behind it. The tympanometer introduces a continuous, low-frequency tone, typically 226 Hertz, into the sealed ear canal. While this tone is playing, the device systematically varies the air pressure within the canal from a positive pressure to a negative pressure and back again.
As the air pressure changes, the eardrum’s ability to vibrate is measured by a microphone within the probe. The amount of sound energy reflected back from the eardrum is recorded, which measures the middle ear’s acoustic admittance or compliance. When the pressure in the ear canal matches the pressure in the middle ear space, the eardrum achieves maximum mobility and absorbs the most sound energy. At this peak movement, the least amount of sound is reflected back, providing the core diagnostic data.
What Happens During the Tympanometry Test
The procedure begins with a healthcare provider visually examining the ear canal and eardrum (otoscopy) to ensure the ear canal is clear of excessive earwax or foreign objects. The patient is asked to remain still, quiet, and refrain from swallowing or talking during the brief test. A small, soft-tipped probe is then gently placed into the ear canal to create an airtight seal.
Once the seal is established, the device automatically begins its cycle of pressure changes, which usually lasts only a few seconds per ear. The patient may feel a slight, temporary sensation of pressure building or releasing, similar to the feeling experienced during a change in altitude. The tympanometer records the eardrum’s responses, which are immediately plotted onto a graph called a tympanogram. This test is painless and quick, making it suitable for patients of all ages, including young children.
Interpreting the Tympanogram Results
The resulting tympanogram is a graph that plots acoustic admittance (eardrum mobility) on the vertical Y-axis against air pressure in decapascals (daPa) on the horizontal X-axis. Interpreting the shape of this graph provides specific information about the middle ear’s condition, with results categorized into three primary types based on the peak’s location and shape.
A Type A tympanogram is considered normal and indicates a healthy middle ear system. This graph features a distinct, sharp peak that occurs at or very near 0 daPa, showing maximum eardrum mobility. This result suggests the middle ear is clear of fluid, and the Eustachian tube is functioning correctly to equalize pressure.
The Type B tympanogram is represented by a flat or rounded line with no discernible peak, indicating the eardrum is not moving significantly in response to pressure changes. This pattern suggests fluid filling the middle ear space, often associated with otitis media with effusion. If the graph is flat, the provider checks the ear canal volume measurement to differentiate between middle ear fluid and an eardrum perforation. A high ear canal volume with a flat tracing indicates a hole in the eardrum or a patent tympanostomy tube, since the middle ear space is included in the volume measurement.
A Type C tympanogram shows a normal peak shape, but it is shifted significantly into the negative pressure range, typically at or below -100 daPa. This negative pressure peak suggests that the middle ear pressure is lower than the surrounding atmospheric pressure, often indicating Eustachian tube dysfunction. This result often occurs during or after an upper respiratory infection or allergy flare-up. Monitoring a Type C result is important because persistent negative pressure can sometimes lead to the development of middle ear fluid.