Abstract
An apparatus for the measurement of the acoustic impedance of the middle ear at the tympanic membrane was described. The measurement of fers a possibility of studying the acoustic structure of the middle ear, which contains not a single but several anti-resonance peaks. The method employed makes use of a main rigid-walled tube linked to an exponential horn with an extended tube of 4.7em length which is inserted into the auditory canal. The source of sound is attached to the main rigid-walled tube which incorporates a travelling probe microphone which is operated by a hand crank. The results of measurements in normal subjects sand in those with conduction affections exhibi. ted acoustic impedance ranging from 900 to 3000cps according to specific property of the exponential horn. The normal impedance is higher in a lower frequency range and lower in a higher frequency range, and is lower than that of otosclerotie ears with fixed stapes, chronic adhesive otitis or tubal occlusion. On the other hand the impedance of the ears with an interrupted ossicular chain is markedly low compared with that of the normal ears. Consequently, results obtained in the living subject can be applied clinically to the assessment of middle ear functions.
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