Tympanometry is a diagnostic procedure used to assess the function of the middle ear. It serves as an objective, quick, and non-invasive method to evaluate the ear’s ability to transmit sound. It helps identify potential hearing issues by providing insights into the middle ear system.
What Tympanometry Measures
Tympanometry evaluates three physical properties of the middle ear essential for sound transmission. It measures the eardrum’s movement, known as compliance or static admittance, which indicates how freely the eardrum responds to pressure changes. The test also assesses the air pressure within the middle ear cavity, comparing it to the external ear canal pressure. Finally, tympanometry determines the volume of the ear canal, from the probe tip to the eardrum or any perforation.
How the Measurement is Taken
The tympanometry procedure involves placing a small, soft-tipped probe into the ear canal, creating an airtight seal. This probe contains an air pump, a speaker that emits a low-frequency sound tone, and a microphone. The device systematically changes the air pressure within the ear canal, ranging from positive to negative pressure. As pressure changes, the eardrum’s movement in response to the sound tone is measured by the microphone. The collected data is charted on a graph called a tympanogram, which visually represents the eardrum’s mobility and middle ear pressure.
Common Conditions Tympanometry Helps Identify
Tympanometry identifies various middle ear conditions that can affect hearing. It commonly helps detect otitis media with effusion, which is fluid behind the eardrum. A flat tympanogram often suggests this condition. The test can also indicate an eardrum perforation, a hole or tear in the eardrum. In such cases, an unusually large ear canal volume is measured.
Eustachian tube dysfunction, where the tube connecting the middle ear to the back of the throat does not open and close properly, can also be identified. This often results in negative pressure within the middle ear. Otosclerosis, a condition involving the stiffening of the small bones in the middle ear, can show reduced eardrum mobility. Cerumen impaction, or earwax blockage, can also be detected if it completely occludes the ear canal, resulting in an abnormally small ear canal volume.
Understanding Tympanometry Results
The results of a tympanometry test are typically displayed as a graph called a tympanogram, which plots ear canal air pressure against eardrum compliance. These graphs are categorized into different types, most commonly Type A, Type B, and Type C, based on their shape and peak characteristics.
A Type A tympanogram shows a sharp peak around 0 daPa (decapascals), indicating normal middle ear pressure and healthy eardrum mobility. This suggests that the middle ear system is functioning as expected.
Variations like Type As (shallow peak) can suggest reduced eardrum movement, potentially due to conditions such as otosclerosis or scarring. Type Ad (deep peak) indicates excessive eardrum movement, which may be associated with a hypermobile eardrum or a disarticulated ossicular chain.
A Type B tympanogram appears as a flat line with no distinct peak, signifying minimal to no eardrum movement. This pattern often points to fluid accumulation in the middle ear, such as in otitis media with effusion, or an ear canal completely blocked by earwax. If the ear canal volume is unusually large with a flat line, it can indicate a perforation in the eardrum or a patent tympanostomy tube.
A Type C tympanogram features a peak that is shifted to the negative pressure side, typically below -100 daPa. This indicates negative pressure within the middle ear, often associated with Eustachian tube dysfunction or the early or resolving stages of a cold or ear infection. Understanding these different tympanogram types helps healthcare providers interpret the test results and guide further diagnostic or treatment decisions.