impedanometrie

Impedanometrie, also known as impedanometry, is a diagnostic method used to assess the mechanical properties of the middle ear by measuring acoustic impedance or admittance across a range of ear canal pressures. The test provides objective information about middle ear function, the status of the tympanic membrane and ossicular chain, and can aid in evaluating Eustachian tube function. It is commonly used in pediatric and general audiology, as well as in otology for preoperative assessment and postoperative follow-up.

The technique relies on a tympanometer, which is placed in the external auditory canal to create a controlled air-pressure environment. A calibrated probe tone (commonly around 226 Hz in adults) is emitted, and the reflected sound is recorded by a microphone. By varying the ear canal pressure, the device yields a tympanogram that plots tympanic membrane admittance (or impedance) against pressure, reflecting the mobility of the tympanic membrane and the middle-ear system. In some cases, higher-frequency probe tones may be used, particularly in infants, to improve sensitivity. Acoustic reflex testing may accompany impedanometry to assess the contraction of the stapedius muscle in response to loud sounds.

Interpretation centers on tympanogram shapes and measurements such as peak compliance, middle-ear peak pressure, and tympanometric width. Common patterns include:

- Type A: normal middle-ear pressure and mobility.

- Type B: flat curve, often indicating middle-ear effusion, perforation, or collapsed canal.

- Type C: negative middle-ear pressure suggesting Eustachian tube dysfunction.

Subtypes like As (reduced compliance) and Ad (excessive compliance) describe stiffness or hypermobility of the middle-ear system.

Limitations include dependence on a proper seal, absence of cerumen obstruction, and interpretation within the broader clinical and audiometric context. Impedanometrie is a complementary tool, not a standalone diagnostic measure for all otologic conditions.