Vibration analysis of human middle ear and an application for clinics for tympanoplasty -Development of prediction method for hearing ability restoration

摘要

A geometric model of the human middle ear was constructed using SolidWorks based on the CT scanning data of a healthy subject. By harmonic vibration analysis, frequency response characteristics of the stapes displacement in sound conduction was clarified. The average displacement of the stapes at a sound pressure of 90 dB is about 5.0 nanometers, which was used as a standard value in our study. Assuming a case in which the auditory ossicles were deficient, a reconstruction model using the columella, instead of the damaged incus, was constructed and analyzed, and the frequency response characteristics of the stapes were clarified. We have proposed a new method for estimating the hearing restoration effect prior to the tympanoplasty operation by comparison of the difference of the stapes displacement between a healthy subject and the reconstruction model. In this study, the model which variously changed the shape (thickness and height) of the annular ligament was analyzed in order to clarify the difference between the frequency response characteristics. Furthermore, the difference when the tympanic membrane is divided into three regions (of which the rigidity differs) was compared with a single region model. The influence that the modeling method of the stapedial annular ligament and the tympanic membrane gives to the frequency response characteristics cannot be ignored. However, the simplified geometric model can be applied to predict the hearing restoration effect. As a clinical application, reconstructive surgery models of the auditory ossicles, in which the ossicular chain was damaged by chronic otitis media, were constructed in multiple operation types. From the vibration analysis of these models, the possibility of our proposal for reconstruction of the auditory ossicles was verified. The validity of our method was confirmed by clinical applications. Finally, the efficacy of predicting the hearing restoration effect prior to the operation was verified.