IMPROVEMENT OF SOUND CONDUCTION EFFICIENCY FROM THE VIEWPOINT OF VIBRATION CHARACTERISTICS OF THE HUMAN MIDDLE EAR

摘要

When the middle ear is damaged by various ear diseases, the linkage of the auditory ossicles may be reconstructed using the column article called the columella, or artificial stapes. In tympanoplasty, operations are carried out based on the workmanship and experience of the surgeon. We have proposed a new method for estimating the hearing restoration effect prior to the tympanoplasty operation. In this method, a geometric model of the human middle ear is constructed using SolidWorks based on CT scanning data. Then, frequency response characteristics of the stapes displacement in sound conduction are calculated using finite element harmonic vibration analysis. The hearing restoration effect can be estimated by a comparison of the differences in the stapes displacement between the reconstruction model and a healthy subject. Through the study of our method, it has been clarified that a maximum displacement of 5.0 nm of a Ill-i type operation model for chronic otitis media achieves a response of about 98% compared to a healthy subject. Furthermore, several models in which an annular ligament becomes more rigid through otosclerosis and related operation models using artificial stapes are constructed and analyzed. As much as the annular ligament stiffened, it followed that sound conduction efficiency decreased. Frequency characteristics of the conductive hearing loss due to otosclerosis thus could be reproduced. According to operation models using artificial stapes, it is possible that the stapes displacement increases, that is, the sound conduction efficiency is improved, more than the result in which an annular ligament becomes highly rigid. From the vibration analysis of these models, our proposed estimation method for reconstruction of the auditory ossicles was verified. Through this study, the optimization of structures and materials for columella and artificial stapes becomes possible. Finally, the efficacy of predicting the hearing restoration effect prior to an operation was verified.