A tympanometer is a specialized medical device used to evaluate the function of the middle ear. It helps healthcare professionals understand the health of the eardrum, also known as the tympanic membrane, and the air-filled space behind it. This non-invasive and quick test assesses how effectively sound travels through the middle ear structures. The primary purpose of tympanometry is to identify potential issues that might affect hearing, offering insights into conditions that cannot be determined by a standard hearing test alone.
How a Tympanometer Works
A healthcare provider gently places a small probe, attached to the tympanometer, inside the ear canal. This probe creates an airtight seal, essential for accurate measurements. The probe contains three components: a speaker that emits a low-frequency sound tone (typically 226 Hz for adults), a microphone to measure the reflected sound, and a pump to change the air pressure within the sealed ear canal.
As the air pressure in the ear canal is systematically varied, the tympanometer measures how the eardrum moves in response to the emitted sound. The eardrum’s movement, or compliance, changes with different pressures. The microphone records sound waves reflected by the eardrum. These measurements are then plotted on a graph called a tympanogram, which visually represents the eardrum’s mobility at various pressures.
Conditions Diagnosed by Tympanometry
Tympanometry diagnoses a range of middle ear conditions by assessing how well the eardrum and middle ear system transmit sound. One common issue it helps detect is middle ear fluid, often associated with otitis media with effusion, where fluid buildup behind the eardrum can restrict its movement. A flat tympanogram, showing reduced eardrum mobility, often indicates the presence of such fluid.
The test can also identify eardrum perforations, which are tears or holes in the tympanic membrane. In such cases, the tympanometer will show a significantly larger ear canal volume than normal, as the air pressure escapes through the perforation. Tympanometry also helps diagnose Eustachian tube dysfunction, a condition where the tube connecting the middle ear to the back of the throat does not open or close properly, leading to abnormal pressure in the middle ear. Issues with the ossicles, the tiny bones in the middle ear, such as stiffness or disarticulation, can also be suggested by the eardrum’s movement patterns.
Interpreting Tympanogram Results
Tympanogram results display air pressure in decaPascals (daPa) on the horizontal (X) axis and eardrum compliance in milliliters (mL) on the vertical (Y) axis. Different shapes of the tympanogram curve indicate various middle ear conditions. The most common types are A, B, C, As, and Ad.
A Type A tympanogram is considered normal, characterized by a distinct, mountain-shaped peak located around 0 daPa, typically within the range of -100 to +100 daPa. This indicates that the eardrum moves normally and that the pressure in the middle ear is balanced with the ear canal pressure.
A Type B tympanogram appears as a flat line with no discernible peak, regardless of pressure changes. This flat tracing often suggests limited eardrum movement due to fluid accumulation in the middle ear, such as otitis media with effusion. If the ear canal volume is significantly larger than normal with a Type B curve, it can indicate a perforated eardrum or the presence of a patent grommet (ear tube).
A Type C tympanogram also has a peak, but it is shifted significantly to the negative pressure side of the graph, typically below -100 daPa. This indicates negative pressure in the middle ear, which can be a sign of Eustachian tube dysfunction, often seen before or after a middle ear infection, or with allergies or a cold.
A Type As tympanogram, similar to Type A, shows a peak around 0 daPa, but the peak is notably shallower. The “As” stands for “shallow” or “stiff.” This pattern suggests reduced compliance or increased stiffness of the middle ear system, which can be caused by conditions like otosclerosis (hardening of the middle ear bones) or myringosclerosis (scarring of the eardrum).
A Type Ad tympanogram displays a peak unusually tall or “deep,” indicating very high compliance or hypermobility of the eardrum. The “Ad” stands for “deep” or “disarticulation.” It may suggest a disconnected ossicular chain (misaligned middle ear bones) or a healed eardrum perforation resulting in a thin, floppy eardrum. While these interpretations provide strong indications, a definitive diagnosis should always be made by a medical professional who considers the tympanogram results alongside other clinical findings.