Understanding Tympanometry

There are many tests which makeup through evaluation and act like pieces of a puzzle which when put together helps to determine the type and cause of hearing loss. Tympanometry is a type of test which is helpful in determining if the hearing loss can be helped by hearing aid or any medical treatment is available to treat it. This method is used to assess the functioning of the middle ear. Tympanometry represents its results in the form of a graph called a tympanogram.

It was developed by Terkildsen et al in 1950’s for measuring middle ear pressure. It has contributed a lot to clinical diagnosis and has become a routine part of the audiological test battery. The probe tone offered by tympanometer is 226 Hz, though it can give different results on other frequencies. This tone has some advantages when testing adult ear because it is stiffness dominated at this frequency. And also the effect of mass and friction will be minor.

Tympanometer consist of the following; air pump, a probe with a loudspeaker, a microphone, and a manometer.

This method is used to diagnose disorders which may lead to hearing loss, especially children. The tympanic membrane is a thin tissue separating the middle and outer ear segments from each other. For your child tympanometry may be performed every week for several months to figure out the change in the fluid over time.

Tympanogram represents the relationship between air pressure in the ear canal and the movement of the eardrum, or tympanic membrane, and the tiny bones in the air-filled middle ear space.

As soon as the eardrums are disturbed with any type of voice, some part of it is absorbed and sent through the middle ear while the remaining sound is reflected back. Tympanometry provides some extra information Eustachian Tube Functioning.

How is Tympanometry performed?

Tympanometry is performed by a hearing healthcare professional or a doctor. Firstly ear canal and eardrum are inspected visually and then using a lighted scope (otoscope). It should be checked if there is no earwax or a foreign object obstructing the eardrum. Then another instrument will be placed in the ear i.e. a probe with flexible rubber tip. The probe will cause a change in the air pressure of the ear canal as you hear some low-pitched tones. This pressure change feels similar to that of takeoff and landing of a plane, which may be uncomfortable. Measurement of your eardrum’s movement will be taken and recorded as the pressure keeps changing.

Moving, speaking, or swallowing during the test may give incorrect results. If a child is there for tympanometry, he/she should be explained about the test beforehand with the help of a dummy. This will prepare them for the loud noises and practice being still.

It will maximum take two minutes for both the ears. People from any ages bracket can have tympanometry, as there is no risk related it.

Interpreting the Tympanometry Results

Tympanometry result indicates; ear canal volume (cm3), the max pressure (daPa) and the peak compliance (ml). The test plays a crucial role in distinguishing between conductive hearing loss and sensorineural hearing loss. And it also allows us to view the upper auditory pathways and the reflex contraction of the middle ear muscles.

Normal Results:
  • No fluid in the middle ear
  • Smooth Eardrum
  • Normal Pressure in the middle ear
  • Normal movement of conduction bone and eardrum

This test can be performed on both adults and infants since no risk is involved in it. Even if the results are normal it can provide information regarding fluid or any middle ear concerns. Presence of fluid in middle ear space may not allow movement of eardrum and transmission of sound. The condition is temporary and can be treated medically. This condition may not require the use of hearing aid to correct the hearing loss but must consult a physician.

Normal pressure in the middle ear varies from +50 to -150 deca pascals (daPa). Decapascals is the measurement unit of air pressure.

Abnormal Results:
  • Presence of fluid in the middle ear
  • Eardrum blocked by earwax
  • Perforation of the tympanic membrane
  • Scarring of tympanic membrane from the frequent ear infection
  • Tumors in the middle ear
  • Pressure beyond normal range in the middle ear
  • Lack of contact in conduction bones of the middle ear
  • Middle ear infection
  • Some problem with the Eustachian Tube

Some other tests should also be performed to diagnose the condition. After getting abnormal test results, the doctor will conduct some additional tests and a follow-up appointment with a specialist.

Classification of Tympanogram

The graphs obtained after conducting Tympanometry are classified into following types based on the compliance and the peak of the graph:

Type A
  • Normal functioning of the middle ear
  • Compliance from 0.3-1.5 ml
Type AD
  • Highly Compliant middle ear system
  • Compliance more than 1.5 ml
Type AS
  • Less Compliant middle ear system
  • Compliance less than 0.3 ml
Type B
  • Middle ear involvement from fluid or middle ear effusion
  • No identifiable peak in the graph
  • Normal ear canal volume
Type B-High
  • Middle ear involvement from a perforation
  • No identifiable peak in the graph
  • Normal limit exceeded by ear canal volume equivalently, much more than 1.5 cm3
Type C
  • Eustachian Tube dysfunctions, just seen before or after effusion
  • Compliance from 0.3 to 1.5 ml

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