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Proceedings Paper

Approach to evidence of middle ear occlusion effect by laser vibrometry
Author(s): Uwe Vogel; Thomas Zahnert; Gert Hofmann; Karl-Bernd Huettenbrink
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Paper Abstract

In the beginning of the last century German anatomist E. H. Weber first reported an audiological phenomenon. Up to now Weber's test is widely used by the otologists for the differentiation of sound conduction and inner ear disorders. The sound of an excited tuning-fork on the top of the head will be lateralized into the ear with an occluded ear canal (occlusion effect). But so far there has been no objective criterion for this effect on humans or temporal bone preparations. We have performed various approaches for the measurement of the occlusion effect. The slow cortical acoustical evoked potentials (SAEP) on both sides after bone conduction stimulation of the vertex at several test persons. We succeeded in proving a decrease of latency during occlusion of ear canal. This has been an electrophysiological approach. However, the theory gives reasons for this effect by changed acoustical impedance conditions of the ear canal due to its occlusion. The related increased sound pressure level (SPL) inside the ear canal results in unilateral amplification effect and its transfer via the middle ear into the inner ear, and therefore performs a lateralization. Thus one should be able to measure this amplification in temporal bone preparations too. Laser vibrometry allows a non-contact access to the tympanic membrane and the middle ear apparatus. The tympanic membrane transforms the ear canal's amplified sound pressure into increased mechanical vibration of the ossicular chain and eventually the stapes footplate affecting the inner ear liquid. That is why we positioned the beam of a laser vibrometer at the inner ear side of the footplate. The preparation was broadband-excited by a bone conduction vibrator. During occlusion of the ear canal an increased sound pressure level inside the ear canal was registered by a probe microphone. By assuming a transfer of this SPL increase onto the footplate we measured its displacement by laser vibrometry. Generally lower gains could have been proven only compared to subjective evaluation (audiometry) or SAEP derivation. Furthermore the effect was detected within limited excitation level and frequency ranges. This is explained by the changed impedance conditions at the foot plate termination due to the removed inner ear, combined with phase differences during osteophony into the ear canal and along the ossicular chain ligaments respectively. Unfortunately there are several problems regarding bone conduction stimulation of temporal bone preparations. Especially the strained fixation of the preparation in relation to the exciting vibrator had to be considered.

Paper Details

Date Published: 11 December 1996
PDF: 8 pages
Proc. SPIE 2927, Optical and Imaging Techniques for Biomonitoring II, (11 December 1996); doi: 10.1117/12.260659
Show Author Affiliations
Uwe Vogel, Technische Univ. Dresden (Germany)
Thomas Zahnert, Technische Univ. Dresden (Germany)
Gert Hofmann, Technische Univ. Dresden (Germany)
Karl-Bernd Huettenbrink, Technische Univ. Dresden (Germany)

Published in SPIE Proceedings Vol. 2927:
Optical and Imaging Techniques for Biomonitoring II
Hans-Jochen Foth; Renato Marchesini; Halina Podbielska M.D., Editor(s)

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