EXPERIMENTAL STUDY ON BONE CONDUCTION WITH TMPAIRED MOBILITY AT THE OVAL AND THE ROUND WINDOW

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  • SAWASHIMA M.
    The Department of Oto-Rhino-Laryngology, Faculty of Medicine, University of Tokyo

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  • 骨導聴力における前庭窓,蝸牛窓の意義に関する実験的研究
  • コツドウ チョウリョク ニ オケル ゼンテイ マド , カタツムリ マド ノ イギ ニ カンスル ジッケンテキ ケンキュウ

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The cochlear microphonics of the cat for bone conducted sound was recorded before and after fixation of the stapes and the round window membrane. The incudostapedial joint of the cat was destructed beforehand to isolate compressive bone conduction from other mechanisms, of bone conduction.<br> The decrease of the cochlear microphonic response was observed by 10 dB after fixation of the round window membrane.<br> By immobilization of the stapes the response was also reduced as much as 10 or 20 dB par-ticularly in frequencies from 1000 to 3000 cps.<br> The most severe impairment of the response was observed after blocking of both win-dows ; the impairment reached 30 dB in some cases.<br> We observed further the complete recovery of the impaired response after the removal of the fixation. Thus we ascertained that the impairment was caused by mechanical disturbance of the windows without any damage in the inner ear.<br> The fact that the response decreased by the immobilization of the stapes in animal experi-ment was in good agreement with Careart's notch of bone conduction curve in otosclerosis.<br> On the other hand, according to the theory of compressive bone conduction, the response or the hearing must increase with immobile stapes. So we concluded that the theory of comp-ressive bone conduction was not adequate for explaining experimental and clinical findings on bone conduction.<br> Consequently we concluded that the inertia of the inner ear conduction system must be considered as another mechanism of bone conduction.

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