tympanometer

A tympanometer, also called tympanometer, is an instrument used to evaluate the function of the middle ear by measuring the mobility of the tympanic membrane in response to controlled changes in air pressure within the ear canal. The device seals the canal with a probe, delivers a brief sound stimulus, and measures the amount of sound energy reflected back. By varying ear-canal pressure from positive to negative, it produces a tympanogram, a plot of middle-ear admittance (or compliance) versus ear-canal pressure.

Key measurements include tympanometric peak pressure (TPP), static admittance (compliance), and ear canal volume. A normal tympanogram is Type A, with a peak near ambient pressure and typical compliance. Type B yields a flat tracing, indicating little or no tympanic membrane movement and often reflecting middle-ear effusion, perforation with occlusion, or a blocked probe. Type C shows a peak at negative pressure, suggesting eustachian tube dysfunction or negative middle-ear pressure. Subtypes As (stiff membrane) and Ad (hypermobile membrane) describe reduced or exaggerated tympanic membrane mobility, respectively.

Clinical uses include assessing middle-ear status in adults and children, diagnosing otitis media with effusion, evaluating eustachian tube function, planning or monitoring treatment, and screening before surgery. Limitations include the need for a good seal and patient stillness, potential interference from cerumen or canal obstruction, and the fact that tympanometry reflects middle-ear mechanics rather than inner-ear function. Tympanometry is typically interpreted alongside audiometry and clinical examination.