Standardized measurements of the sound transmission of middle ear implants using a mechanical middle ear model |
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Authors: | H Meister M Walger A Mickenhagen H von Wedel E Stennert |
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Affiliation: | (1) ENT Department, University Hospital of Cologne, Joseph-Stelzmann-Strasse 9, D-50931 Cologne, Germany, DE |
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Abstract: | Several ways to evaluate the sound transmission properties of middle ear implants are now established. Besides computer-based
simulations using acoustic and electrical analog circuits or finite element analysis, measurements can be performed with temporal
bone preparations. Experiments with these preparations consider various anatomical properties, but a large number of parameters
influence the outcome of measurements. To facilitate standardized measurements, a mechanical middle ear model was developed
that allows comparison of the transfer function of middle ear implants on defined conditions. The model approximates the impedances
of the tympanic membrane and inner ear with the aid of thin, flexible membranes. The implants are fit between the membranes,
and displacement at an artificial stapes footplate is measured with an optical probe. Fundamental influences on the sound
transmission properties of nine different middle ear implants (total ossicular replacement prostheses) were examined. Although
the material and shape were different, some of the prostheses revealed very similar transfer functions. The mass of the implant
showed the largest influence on sound conduction. With a higher mass, the frequency area above approximately 1 kHz was found
to be significantly deteriorated. The lightest implant used was 4 mg and showed the best overall results. These findings show
that middle ear prostheses should be as light as possible for optimum high-frequency transmission.
Received: 24 May 1998 / Accepted: 9 July 1998 |
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Keywords: | Mechanical middle ear model Middle ear prosthesis Sound transfer function Optical probe |
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