Tympanometry

Also known as: Acoustic impedance audiometry

Tympanometry is an objective diagnostic method that assesses the functional status of the middle ear by measuring the mobility of the tympanic membrane and the ossicular chain. The method is based on registering the sound energy reflected from the tympanic membrane as the air pressure in the external auditory canal is altered.

The results are presented as a graph — a tympanogram — which clearly illustrates the function of the middle ear. Tympanometry is a fast, non-invasive, and highly informative test widely used in otorhinolaryngology and audiology.

Principle of the Method

The test is based on the concept of acoustic impedance — the resistance the middle ear system exerts on a sound wave. A flexible, elastic tympanic membrane conducts sound well (low impedance), while a rigid, immobile system (e.g., when there is fluid in the middle ear) reflects most of the sound energy back (high impedance).

The procedure is performed with a special instrument called a tympanometer. A probe is tightly inserted into the external auditory canal; it contains three channels:

Sound generator: Emits a probing tone of constant frequency (usually 226 Hz) into the ear.
Microphone: Measures the intensity of sound reflected from the tympanic membrane.
Air pump: Alters the air pressure in the sealed auditory canal from positive to negative.

The device records the pressure at which the tympanic membrane is most mobile (i.e., reflects the least amount of sound). This occurs when the pressure on both sides of the membrane is balanced.

Types of Tympanograms and Their Interpretation

The shape of the resulting graph (tympanogram) allows conclusions to be drawn about the presence or absence of pathology in the middle ear.

Interpretation of tympanometry results

Type	Graph description	Interpretation
Type A	Sharp peak with the apex at near zero pressure (from +50 to -100 daPa)	Normal. Indicates normal middle ear pressure and good mobility of the tympanic membrane and ossicles
Type B	Flat or slightly curved line without a prominent peak	Fluid in the middle ear (exudative otitis media) or tympanic membrane perforation. Indicates lack of mobility of the tympanic membrane
Type C	Normal-shaped peak, but shifted to the negative pressure area (below -100 daPa)	Eustachian tube dysfunction. Indicates negative pressure in the middle ear
Type As	Normal-shaped peak, but low and flat	Stiffness (reduced mobility) of the ossicular chain. May be observed in conditions like otosclerosis
Type Ad	Very high peak, often extending beyond the graph limits	Hypermobility of the tympanic membrane. May indicate a ossicular chain discontinuity or tympanic membrane atrophy

Clinical Role

Tympanometry is a key method for diagnosing exudative otitis media, especially in pediatric practice, as it is a common cause of hearing loss in children. The test aids in the differential diagnosis of conductive and sensorineural hearing loss: in sensorineural hearing loss, the tympanogram is typically normal (Type A). The test is also used to assess Eustachian tube function, monitor the effectiveness of middle ear disease treatment, and check the patency of tympanostomy tubes (ventilation tubes).

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