CLINICAL STUDIES ON THE CHANGES IN HEARING INDUCED BY THE BLOCKING OF THE TYMPANIC MEMBRANE IN THE EAR WITH FENESTRATION OPERATION:Part 1.Study on the Mechanism of Sound-Transmission after Fenestration Operation
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概要
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Although fenestration operation improves the hearing of the ear with clinical otosclerosis, the improvement is within certain limits because of the lack of the normal mechanism of sound transmission.The expected improvement of the air conduction threshold has been thought to be 20_??_25 db when the bone conduction threshold is within normal limits.The blocking of the tympanic membrane of the fenastrated ear alters its hearing acuity.The author carried out clinical investigation on these changes in hearing and gave a consideration on the mechanism of sound transmission after the fenestration operation.Fifteen ears consisting of 12 ears with complete fixation of stapes and 3 ears with incomplete fixation of stapes were selected for this study, including a case in which the fenestral bony closure was observed six months after the operation and the patient was operated again.The tympanic membrane of the fenestrated ear is blocked with cotton pellet soaked with 0.2cc of 1% acrinol cod-liver oil, and air-conduction threshold values before and after the blocking were compared.The test was repeated at the intervals of one month, 6 months, and one year after fenestration operation, and the following results were obtained.1.By the observations made during the fenestration operation and postoperative hearing improvement, it has been verified that otosclerosis occurs among Japanese as well.2.There are two pathways of the sound transmission after fenestration, namely, by the way of new fenestra, and the other via the round window.The new fenestra is considered to be superior than the round window as far as the transmission of the sound energy to the labyrinth is concerned.3.In the majority of the cases whose tympanic membrane of the fene3trated ear is blocked with the cotton pellet soaked with 1% acrinol cod-liver oil, hearing is markedly improved in the low and middle ranges of frequency, i.e.at the neighborhood of 250 cps and 500 cps, but hardly any change can be recognized in the high ranges of frequency.4.In some cases, no changes in hearing in the fenestrated ear are observed after the blocking of the tympanic membrane, The degree of fixation of stapes, and the condition of air conduction thresholds before the blocking of the tympanic membrane seem to be responsible for such condition.Moreover, in the case having bony closure of new fenestra in 6 months after fenestra- tion operation, the hearing decreased by the blocking of the tympanic membrane.5.The change in hearing by the blocking of the tympanic membrane in the fenestrated ear seems to have no causative relationship with postoperative serous labyrinthitis.6.The mechanism of the change in the hearing by the blocking of the tympanic membrane in the fenestrated ear seems to be the following:The amplitude of the sound waves entering through the round window are decreased by the blocking of the tympanic membrane, with the concomitant change in the phase, and a considerable difference in the sound pressure between the new fenestra and the round window makes the vibration of the endolymph easier than before the blocking, accelerated by the change of phase.
- 一般社団法人 日本耳鼻咽喉科学会の論文