Audiometer: Impedance (Tympanometry)

This chapter discusses the purpose, principle of operation, specifications, and applications of an impedance audiometer. An impedance audiometer is a device designed to test the functional status of the middle ear and mobility of the tympanic membrane and the conduction bones. Impedance audiometry, or most commonly referred as tympanometry, is based on producing variations of air pressure in the ear canal by means of a probe measuring the middle ear's acoustic resistance. In addition to the standard 226 Hz probe tone tympanogram, a higher frequency probe tone can also be employed for tympanometry. Acoustic impedance is considered to be a response to acoustic admittance, which involves the measurement of air pressure or energy flow in the eardrum and associated structures. The acoustic reflex measurements along the impedance curve measurement forms the basis for study of the integrity of the complete middle ear system, which is of great diagnostic value.