Tympanometry is a method for doctors and audiologists to diagnose and monitor problems with the middle ear. It can help with identifying disorders that can cause temporary or permanent hearing loss, especially in children. The test itself involves a brief puff of air in the ear canal. It is painless and measures the ear’s response to both sound and pressure.
The results are recorded on a graph called a “tympanogram”.
It is not that common for a UK audiologist to have access to this equipment as it is very expensive, but we are so equipped. Tympanometry can help reveal or assist in monitoring the following:
- Perforated ear drum
- Scarring of the ear drum
- Fluid in the middle ear
- Impacted ear wax
- Eustachian tube function
- Failure of the conduction bones of the middle ear
- A tumour in the middle ear
A tympanogram measures middle ear function that can add to information already gathered via the visual otoscopic examination. The impedance measurement is a method by which to diagnose and monitor disorders that could lead to permanent hearing loss. This test will produce a “curve” generally falling into 1 of 3 categories:
In a “Type A” curve, the peak compliance occurs at or near the atmospheric pressure, indicating normal condition within the middle ear.
Type A curve has three subcategories:
AD: A deep curve with a tall peak indicates an abnormally compliant middle ear, as seen with ossicular chain dislocation or loss of elastic fibres in the ear drum.
AS: A shallow curve indicative of a stiffened system, as seen in otosclerosis or a thickened tympanic membrane.
A “Type B” curve has no sharp peak and little or no variation in impedance over a wide sweep range. This is indicative of non-compressible fluid within the middle ear space (otitis media), tympanic membrane perforation, or debris within the external ear canal (cerumen).
A “Type C” curve peak compliance is significantly below zero (usually less than -200), indicating negative pressure (sub-atmospheric) within the middle ear space. This finding is suggestive of Eustachian tube dysfunction or middle ear fluid.
Acoustic reflex measurements
An acoustic reflex, or contraction of the Stapedial muscle, occurs under normal conditions when a sufficiently intense sound is presented to the auditory pathway. This contraction of the muscle causes a stiffening of the ossicular chain which changes the compliance of the middle ear system. As in Tympanometry, a probe tone is used to measure this change incompliance.
When the stimulus presentation and measurement are made in the same ear by means of the probe, this acoustical reflex is referred to as an ipsilateral acoustic reflex. When the stimulus presentation and measurement are made in opposite ears, the reflex is referred to as a contralateral acoustic reflex.
An acoustic reflex measurement is taken after the tympanogram is performed. For best results, this reflex measurement is automatically conducted at the air pressure value where the compliance peak occurred during the tympanometric test. Stimulus tones of varying intensities at 500, 1000, 2000 or 4000 Hz are presented as short bursts.
If a change in compliance greater than 0.05 ml is detected, a reflex is considered present. Because this is an extremely small compliance change, any movement of the probe during the test may produce an artefact (false response). The test result is recorded as Pass / No Response and in graphical form.
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