Tympanometry is a procedure that tests the function of the middle ear. It is a test that can help diagnose hearing disorders that may lead to hearing loss, especially in children. It measures the movement of the tympanic membrane in response to changes in air pressure.
The middle ear and its components
The tympanic membrane (TM) is a thin three-layer membrane, cone-like in shape, that separates the middle ear from the outer segments. During otoscopy, it is expected that a healthy, normal TM will reflect a cone of light, a reflection off of the membrane in the anterior inferior portion of the TM. The middle ear is situated behind the tympanic membrane and is responsible for taking the acoustic energy from ear canal and translating it into mechanical energy. The middle ear is an air-filled cavity that houses the ossicular chain, the Tensor tympani and stapedius muscles, and the Eustachian tube, which connects the middle ear and the upper portion of the nasopharynx. The main function of the middle ear is to transfer sound energy to the cochlea a fluid-filled snail-shaped structure. It is through the cochlea that sound waves are transduced into electrical impulses and transported to the brain where they are interpreted as sound.
When is tympanometry conducted?
Tympanometry assesses the normal (or abnormal) functioning of the middle ear system. In other words, the efficiency of the middle ear. The test itself presents both positive and negative pressures accompanied by a constant probe tone. The test measures the amount of absorption or reflection of the probe tone from the middle ear space. Tympanometry is an essential diagnostic tool when conductive hearing loss is suspected. The test is relatively painless and has historically been conducted in hearing healthcare facilities or in the offices of physicians. However, with a portable tympanometer, the test can be conducted just about anywhere. Tympanometry is usually conducted to help determine:
- The presence of pathologies such as otosclerosis Ossicular discontinuity Tympanic membrane perforation Eustachian tube dysfunction/Patulous Eustachian tube
- Eardrum pathology
- Otitis media
- Otitis externa
- Middle ear tumors
What does a tympanometer measure?
Tympanometry collects data to test four basic functions of the middle ear. The results of tympanometry are plotted on a graph called a tympanogram. A trained eye is needed to read and interpret a tympanogram, which can require some practice. A typical tympanometry result indicates the following:
- Equivalent Ear Canal Volume (ECV) is the estimation of the ear canal volume from the front of the probe tip. It is measured in centimeters cubed (cm3) and the normal range can depend on the age of the patient. For example, in ages 3-5 years old, the volume is typically between 0.4-1.0 cc, while the range is between 0.6-1.5 cc for adults.
- Compliance or Static Admittance (SA) is a measure of the maximum amount of acoustic energy absorbed by the middle ear as well as the tympanic membrane.
- Tympanometric Peak Pressure (TPP) or Middle Ear Pressure is an estimation of the pressure in which there is the highest absorption of acoustic energy in the middle ear system. It is measured in decapascals (daPA).
- Tympanometric Width (TW) is defined as the pressure interval in daPA where the horizontal line intersects the tympanogram at 50% of the peak height.
- A gradient is defined as “an objective measure that describes the steepness of the slope of the tympanogram near the peak,” by Fowler & Shanks.
Identifying the Data and Measurements on a Tympanogram
Types of Tympanograms
Tympanograms are classified by types – Type A, B, C, AS, and AD. Each classification indicates a range that falls between normal and abnormal.
- Type A, AS, and AD are considered to be normal
- Type B is considered abnormal, usually indicating that the patient has fluid in the middle ear
- Type C may indicate a blockage or retraction in the eardrum. Patients with a tympanogram graded Type C may need further medical attention.
Components of a Tympanogram
Look for the Y-Axis: Compliance
The compliance of the eardrum measures the flexibility of the eardrum when positive and negative air pressures are applied. The compliance amount indicates how effectively sound is being transmitted into the middle ear and is measured in centimeters cubed (cm3) or millimho (mmho). Look for the Y-axis on the graph which starts at the bottom with 0 and goes to 1.8 at the top in 0.3 increments (0, 0.3, 0.6, 0.9, 1.2, 1.5, 1.8).
Look for the X-Axis: Air pressure
The X-axis represents the air pressure and is measured in millimeters (ml) of H20. On this axis, the increments start at -400 on the left aside and increase by 100 to reach +200 on the far-right side.
Look for a Vertical Line: Ear Canal Volume
The vertical line on the top right side shows the ear canal volume measured in cm3. The ECV results can also be printed at the bottom.
How do you read a tympanogram report?
A tympanogram will show the results of one eardrum at a time. An “L” on the tympanogram indicates the left eardrum; an “R” indicates the right eardrum. A clinician will mainly look at the peak of each graph. The examples below use a 226 Hz probe tone. (Classifications can vary between audiologists, guidelines, countries, and clinics.)
Reading Type A
A Type A grade is considered to be normal. There is no medical attention required. Type A is usually identified by its single peak with equal sides. Type A is indicated by these results on a tympanogram:
- ECV: 0.6 — 1.5 cm3 (adults)
- Static Admittance: 0.3 — 1.4 cm3
- Middle Ear Pressure: -150 to +25 daPa
Type A Interpretation: Normal report. Tympanogram results are within normal limits.
Reading Type AS
The tympanogram is normal but with a low compliance/SA reading. This is a shallow tympanogram that indicates decreased mobility in the middle ear system. The result might range as follows:
- ECV: 0.6 — 1.5cm3
- Static Admittance: <0.3 cm3 in adults
- Static Admittance: between 0.2-0.9 cc in children 3-5 years of age
- Middle Ear Pressure: -150 to +25 daPa
Type AS Interpretation: Type AS reading shows abnormally reduced static compliance/admittance, consistent with middle ear pathology.
Reading Type AD
High compliance/static admittance indicated by a curve can indicate an overly mobile tympanic membrane or middle ear system. Type AD range might be as follows:
- ECV: 0.6: 1.5 cm3
- Static Admittance: > 1.4 cm3
- Middle Ear Pressure: -150 to +25 daPa
Type AD Interpretation: Type AD reading shows abnormally increased compliance, indicating hypermobility of the tympanic membrane.
Reading Type B
A Type B tympanogram will have no peak (flattened curve), non-measurable or reduced middle ear pressure, and reduced static compliance. The range might be:
- ECV: 0.6 — 5 cm3 (low)
- ECV: > 2.5 cm3 (high range), if perforation is present or pressure equalization tube is patent
- Static Admittance: Not present or greatly reduced
- Middle ear pressure: Not present or greatly reduced
Type B Interpretation: In most clinics, Type B reading is considered abnormal as it shows no measurable pressure or static compliance/admittance and is consistent with middle ear pathology. ECV can be in the low- to high range, indicating cerumen impaction/occlusion or a tympanic membrane perforation, respectively.
Reading Type C
The reading shows a low peak that shifts unevenly in the left quadrant that demonstrates negative pressure in the middle ear. The range might be as follows:
- ECV: 0.6 –5 cm3
- Static Admittance: 0.3 — 4 cm3
- Middle Ear Pressure: > – 150 daPa
Type C Interpretation: These tympanometric results typically indicate significant negative pressure which could be consistent with middle ear pathology. Such patients need to be monitored to check the transition of a fluid into the middle ear because of a retracted tympanic membrane, as it could indicate Eustachian tube dysfunction.
A portable tympanometer that goes where you go
The KUDUwave Pro TMP is a portable audiometry system that integrates bilateral tympanometry for the very first time in the history of audiology. Dual tympanometers are integrated into each KUDUwave earcup enabling tympanometry of both ears without having to switch ears. This makes it easier to test children and also speeds up the testing time significantly.
Dr. Heather Malyuk, Editor
Dr. Malyuk works as a co-investigator with Gateway Biotechnology Inc. and The University of Akron where she studies the effects of sound exposure on hearing, as well as tinnitus management. Dr. Heather Malyuk is actively involved in the following organizations and has been recognized both nationally and internationally for her work in audiology, sound, and music.