Immittance Testing

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Immittance testing is made up of a series of tests.

Immittance testing is a common audiological evaluation that is important in the diagnostic process. It may be performed alone, as part of an overall hearing evaluation, or in conjunction with any number of other evaluations. If it is part of a hearing evaluation, it is important to understand that each of the tests within the evaluation will serve a separate function.

Purpose

This evaluation may be performed to explore disorders that might result in hearing loss, especially in patients who are children. The test is done to measure how the tympanic membrane moves as it responds to pressure changes. This membrane separates the outer and middle ear. A tympanogram is a type of graph that records the results from tympanometry. Doctors might perform this test to look for:

  • Fluid accumulating in the middle ear
  • A tear in the eardrum
  • An infection in the middle ear
  • A Eustachian tube problem (this tube connects the middle ear with the nose and upper throat)

This test may only need to be performed once to evaluate a problem. However, for monitoring purposes, doctors might choose to do it every few weeks over the course of several months.

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The second test within immittance testing is the acoustic reflex test. There are muscles within the middle ear that involuntarily respond to high-frequency sounds. In healthy conditions, the human ear should respond to sounds in the 70 to 100 dB SPL range. Additionally, the response should be bilateral, meaning that no matter which sound the ear is directed to, the middle ear muscles will react the same in both. During the acoustic reflex test, the reactions of these specific muscles will be tested by introducing sounds to the ears and measuring the response of the muscles with a small probe. This will likely be done in each ear individually and simultaneously, and at various frequencies to determine if there is conductive hearing loss.

The third, and final, part of immittance testing is the acoustic reflex decay test. This test is remarkably similar to the acoustic reflex test, but there are some differences. If there is suspected decay to one ear, the stimulus, or sound, will be introduced to the opposite ear. Meanwhile, the small probe will be placed in the ear with suspected damage to verify the muscular reaction.

It is important to note that all of these tests are minimally invasive and have little risk associated with them. Additionally, they don’t require any patient feedback in order to be accurate, so they are viable among all age ranges.