Finite element analysis of round-window stimulation of the cochlea in patients with stapedial otosclerosis

Abstract

An active actuator coupled to the round window (RW) can transmit mechanical vibrations into the cochlea and has become a therapeutic option of hearing rehabilitation for patients with stapedial otosclerosis. A finite-element model of the human ear that includes sound transmission effects of the vestibular and cochlear aqueducts of the inner ear is adopted in this study for investigating the cochlear response to RW stimulation under stapes fixation. There are two effects due to otosclerosis of the stapes: the fixation of the stapedial annular ligament (SAL) and the increase of the stapes mass. The frequency responses of the middle ear and cochlea with normal and otosclerotic stapes are calculated under sound and RW stimulations. The results show that changes in the material property of the stapes have different effects on the cochlear responses under sound and RW stimulations. Because of the vestibuli aqueduct, the reduction in the low-frequency magnitude of the pressure difference across the cochlear partition due to SAL fixation is much smaller under RW stimulation than under sound stimulation. The results of this study help understand sound transmission during RW stimulation in patients with stapedial otosclerosis.

Research on coupling effects of actuator and round window membrane on reverse stimulation of human cochlea

“…Therefore, it is necessary to analyze the influence of these typical types of middle-ear disorder on reverse stimulation under the influence of coupling effects of actuator and RWM. According to the predicted results of the model about otosclerosis, it can be found that otosclerosis causes the reverse stimulation’s performance to decrease to varying degrees, which is similar to the change trend of | P SV − P ST | predicted by the finite-element model of Zhang et al 19 The resonance response of the coupling impedance model of the human ear and the actuator based on reverse pressure transfer function referenced to actuator velocity is consistent with the impedance model of the human ear based on reverse pressure transfer function referenced to actuator pressure. 45 In contrast, the ossicular chain disarticulation reduces the middle-ear load impedance during reverse stimulation, which slightly improves the reverse stimulation’s performance.…”

“…Since the reverse stimulation is used for treating conductive or mixed hearing loss, the inefficient coupling’s influence in the ear with middle-ear disorder was also investigated by simulating two typical forms of middle-ear disorder: otosclerosis and ossicular chain disarticulation. 19,41 Otosclerosis prevents sound energy into the inner ear, and its typical physiological changes are the hardening of the stapedial annular ligament and the increase in the stapes mass. Hardening of the stapedial annular ligament was simulated by changing its stiffness to 10 times or 100 times the normal value.…”

“…Hardening of the stapedial annular ligament was simulated by changing its stiffness to 10 times or 100 times the normal value. 19,42 The increase in the stapes mass was simulated by changing its mass to five times the normal value. 19,43 Trauma, otitis media, and middle ear deformities cause the ossicular chain disarticulation, and the most common type is the interruption of the incus long process.…”

“…19,42 The increase in the stapes mass was simulated by changing its mass to five times the normal value. 19,43 Trauma, otitis media, and middle ear deformities cause the ossicular chain disarticulation, and the most common type is the interruption of the incus long process. 18,41 In the circuit model, the disarticulation of ossicles is always simulated by a short circuit.…”

“…Moreover, neither the coupling of the actuator with the RWM nor the shunting effect of the third windows was considered. Zhang et al 19 used a finite element model of the human ear to study the effect of otosclerosis, and found that otosclerosis reduces the pressure difference in the cochlea. However, the actuator was directly tied to the RWM, and the influence of the coupling effects of the actuator and the RWM has not been studied.…”