| Defects of cochlear acoustic transmission have a close relationship with some otologic diseases, such as semicircular canal dehiscence (SCD), endolymphatic hydrops and perilymphatic fistula. Though these diseases show different clinical manifestation, they all have organic disorders on the cochlear conductive structure. Among them, semicircular canal dehiscence with the pathology feature of defect of semicircular bone is the typical one. It lead to the bulging of the membranous labyrinth, and lymph pressure recduction. Currently, the pathogenesis of semicircular canal dehiscence was explained by the third window hypothesis, however, there still lack of powerful experiment evidence. We thought that the semicircular canal dehiscence caused the lymph physical properties change, induced the variation of the lymph pressure wave, lead to the statics and dynamics changes of the basilar membrane traveling wave and the lymph in the Corti, and then resulted in the cochlear conductive disorder of the acoustic energy. Study of the change of cochlear lymph pressure wave under semicircular canal dehiscence will help to verify the hypothesis and clarify the pathogenesis. This study discussed the following three parts.Part one Influence of SSCD on the lymph pressure wave in guinea pig and cadavers model.The surgery site of SSCD nearing to vestibular in14guinea pigs were compared to the none-surgery site with vestibular and semicircular HE stain; LDV was used to measure the vibration of tympanic membrane, round window, stapes, and the dehiscence pre and postoperation and after dehiscence repaired; The hair cell were investigate with phalloidin staining.The vibration of tympanic membrane, round window, stapes, and the dehiscence pre and postoperation and after dehiscence repaired were also measured on6thawed cadavers and2fresh one.The HE stain from the post-surgical animal, the model of SSCD on guinea pig was acceptable; There are some energy leakage from the produced third window in the range from300Hz to1500Hz in animal model, with pressure wave increased on vestibular and declined on cochlear, presenting with decreased vibration on the tympanic membrane, stapes, and round window. Vibration recovered after dehiscence repaired. All the hair cells were normal in the phalloidin stain. It was hard to remain the membranous labyrinth on the thawed and fresh cadavers. There is no differences between the vibrations of pre-and post-surgery in the thawed cadavers; in the fresh cadaver, the vibration from the tympanic membrane and stapes were increased, while vibration from the round windows were decreased in500Hz to1200Hz after defects were produced.Part two Influence of different size and site of dehiscence on the lymph pressure wave of guinea pigs.Twenty four guinea pigs divided into4groups, with each of them has6. Based on the position of the defect and its size, the four groups were as follows:1) the produced defect nearing to vestibular with its size of0.5mm×0.5mm,2) the produced defect nearing to vestibular with its size of0.5mm×1.0mm,3) the produced defect being far away from vestibular with its size of0.5mm×0.5mm,4) the produced defect being far away from vestibular with its size of0.5mm×1.0mm. After that, we detect the pre-and post-surgical vibrations of the tympanic membrane, round window, stapes and the surgical sites by using the Laser Doppler Vibrometer (LDV) in all the animals. When we finish measurement, we repaired the produced third windows by using dental bone cement, and detect vibrations of the aforementioned structures again.There are some energy leakage from the produced third window in the range from300Hz to1500Hz in animal model, with pressure wave increased on vestibular and declined on cochlear, presenting with decreased vibration on the tympanic membrane, stapes, and round window. Vibration recovered after dehiscence repaired; Energy leakage from the group2is much more than that from group1in the range of500Hz to1000Hz; Energy leakage from the group1is much more then that from group3in the range of400Hz to800Hz.Part three Influence of SSCD induced third window on the hearing of guinea pigs.The auditory brainstem-evoked potentials (ABR) on the pigs before, after the surgery as well as after repair the defect were detected. The ABR threshold were increased after post-surgical, however, they decreased to normal range after we repair the defects, which did not show any significant differences between the control.In conclusion, model of SSCD on guinea pig and fresh cadaver was reasonable, which can be used for the future study; There are energy leakage from the produced third window in low frequency range in the model, with pressure wave increased on vestibular and declined on cochlear, presenting with decreased vibration on the tympanic membrane, stapes, and round window. Vibration recovered after dehiscence repaired; The same size SSCD nearing to vestibular showed more influence on the lymph pressure wave than the far away one, while in the same site, the large SSCD showed nore influence on the lymph pressure wave than the small one; The hearing decease of guinea pigs SSCD model may induced by the changed of lymph pressure wave and impedance by the third window. |
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