Search

O tolaryngologists have traditionally placed emphasis upon the history, physical examination, and routine pure-tone audiometry in diagnosing middle ear pathology. Recent development of the Zwislocki acoustic bridge has provided an additional objective assessment of ossicular chain function by the measurement of absolute and relative impedance.For general purposes, impedance may be considered as resistance to motion. Acoustic impedance of the middle ear is measured by quantifying the sound energy reflected by the tympanic membrane into the external auditory meatus. The amount of reflected sound energy is directly influenced by conditions of the middle ear. High reflected energy develops when the middle ear system is stiff or heavy as in otosclerosis, adhesive otitis, or cholesteatoma. Low reflected energy occurs When the middle ear system is flaccid and absorbs most of the sound energy as in cases of disarticulation of the ossicular chain. General discussion of the diagnostic value of acoustic impedance

The middle ear impedance of a group of 25 subjects with normal middle ears was studied with the Zwislocki acoustic bridge. The basis for selection of test ears was carefully documented. Average and range of impedance measures were compared to recent data. The effects on impedance readings of operator error in the preliminary measurement of canal volume were also studied.