Research On Sound Transmission Property Of Round Window-Stimulated Middle Ear Implant

Serving as an effective treatment way to compensate sensorineural hearing loss of human,the middle ear implants(MEIs)have made great progress during last decades.The MEIs,compensating hearing loss by direct stimulation to the ossicular chain or round window,have many advantages including elevated speech intelligibility,enhanced high–frequency gain and reduced negative feedback.Such traditional MEI as incus-stimulated and tympanic membrane-stimulated depend on the intact ossicular chain,however,in addition to the sensorineural hearing loss,some patients also suffered from moderate to severe conductive or mixed hearing loss.It is difficult to great majority of these patients to restore their middle ear structure by surgery.Accordingly,the traditional MEIs could not compensate the hearing loss effectively under the above mentioned circumstances.But round window-stimulated(RW-S)MEI could avoid such problems effectively,because that RW-S MEI compensate the hearing loss by cochlear reverse stimulation: it transfers its vibration to cochlear by stimulating the round window directly.Nonetheless,clinical reports show a high variability regarding the degree of hearing compensation performance of the RW-S MEI;additionally,the actual functional gain provided by the round window stimulation is less than the theoretic expectancy.Besides,there is still no any domestic commercial MEI product,and there are numerous hearing loss patients in China.Therefore,it is necessary to develop a set of RW-S MEI which could compensate the hearing loss stably and effectively.Accordingly,this paper was carried out to study the sound transmission property of RW-S MEI to investigate the reasons for the clinical variability from the two aspects of design parameters and the patient's own condition,and then improve the actual gain of RW-S MEI.This work would provide theoretical basis for developing a set of cost-effective RW-S MEI.The specific work in this paper is summarized as follows.The validity of the constructed human ear finite element model which was built via micro-computer tomography imaging and technique of reverse engineering was verified by comparing the model calculated results with experimental data.Based on the finite element model of human ear,the effects of actuator's cross-section,mass and bracing stiffness,the coupling layer's thickness and Young's modulus as well as the round window's preload on the hearing compensation performance of RW-S MEI were systematically explored,and some advice for optimizing RW-S MEI were proposed.The impacts of ossicular chain partial composition missing and otosclerosis on round window stimulation performance were studied,and the results point out that it is essential to specifically improve the output stimulating force of RW-S MEI to make its actual gain being consistent with the theoretical expectancy.The experimental bench which was used to testing the hearing compensation performance of RW-S MEI was built.Based on this testing bench,the dynamic performance of the selected piezoelectric stack was tested.The round window was simulated by physical simplified model,and by utilizing this model,the tendency effect of the actuator's cross-section area and the introduction of the coupling layer on the round window stimulation performance,which was obtained by calculating the finite element model of human ear,was verified.