Impedancemetry is an objective, non-invasive, and painless test used to assess the progression of the sound wave through the middle ear.
Practical tests in Impedancemetry
Impedancemetry – Clinical Impedance Meter Interacoustic AT235
In daily clinical practice, the main tests performed are:
- Tympanometry
- Stapedial reflex
- Tubal tests
Tympanometry
Tympanometry is an objective test that, by increasing or decreasing the pressure in the external auditory canal, measures the changes in energy flow across the middle ear through the tympanic membrane. It provides indirect information about the condition of the middle ear and allows us to establish or confirm the diagnosis of certain pathologies, such as seromucous otitis, or alterations of the Eustachian tube, tympanic membrane, or ossicular chain.
Stapedial Reflex
The stapedial reflex is the involuntary contraction of the stapedius muscle in response to an intense acoustic stimulus (between 70 and 100 dB above the hearing threshold), which increases the stiffness of the tympano-ossicular system, thereby protecting the inner ear from excessive stimulation.
Recording and studying the characteristics of this reflex provides an initial indication of the subject’s hearing level (its presence rules out at least severe or profound hearing loss) and offers information about the integrity of the structures involved. It helps in the diagnosis of diseases affecting the mobility of the tympano-ossicular system or the function of the facial nerve and allows better localization of certain processes affecting the brainstem.
Due to maturational factors, its clinical usefulness should be considered only from 7 months of age.
Tubal Tests
Tubal tests are dynamic studies specifically assessing the function of the Eustachian tube. The most widely used test, in ears with intact tympanic membranes, is the Williams test, which compares the baseline pressure in the middle ear with that recorded after asking the patient to swallow and perform a Valsalva maneuver. The normal difference among these three measurements is 15 to 20 daPa, which decreases when tubal dysfunction is present.