TYMPANOMETER

This is also called a middle ear impedance (or admittance) audiometer or an acoustic impedance meter, although the term is often used to describe a simple automatic machine having a restricted range of facilities. It is used to measure the sound transmission properties of the middle ear (ear drum, malleus, incus, stapes to oval window on the cochlea). It works by applying a known sound pressure to a sealed volume in the outer ear and detecting the sound level changes as the outer ear pressure is varied through a small range above and below the atmospheric pressure. Transmission through the ear drum is best when the delivered pressure is the same as the middle ear pressure (i.e. in the eustachian tube) and it falls off above and below this pressure as the ear drum stiffens as a result of the pressure differential. The resulting graphs of sound transmission against pressure is plotted automatically on an X-Y recorder and is calibrated in either acoustic impedance or as effective air volume.

It is useful for demonstrating pressure in the middle ear when the eustachian tube is blocked and for showing defects in the mechanical transmission mechanism of the small middle ear bones.

Such instruments are used in the audiology department. See also Acoustic impedance meter for further information.

Content and Design Copyright 2000 Dr. Malcolm C Brown.  See Title Page for more details