Spatial motion in natural and reconstructed middle ears and the impact on sound transfer

Abstract

During sound transmission the elements of the middle ear carry out frequency dependent motions in all three spatial directions. Particularly the stapes exhibits a piston and rocking motion and recent studies show that rocking also has an impact on hearing. Here the spatial motions of natural and reconstructed ears are considered on the basis of experiments and numerical simulations based on Multibody System (MBS) approach and Finite Element Method (FEM). In case of a passive reconstruction with a PORP the stapes carries out pronounced rocking motions as well as the piston driven by the natural incus in classical stapedotomy. In the active, electromagnetic middle ear implant Phonak Ingenia, a piston prosthesis is driven by the actuator. Due to anatomical restrictions, the axes of the actuator and the prosthesis are not in line and thus a rocking motion of the prosthesis occurs. Compared to passive reconstructions and the natural ear, this rocking is about in the same range of magnitude. In particular, the coupling between actuator and prosthesis is important for the hearing sensation. Thus, a standardized coupling configuration between the Phonak Ingenia actuator and the piston prosthesis with predefined coupling stiffness and damping offers optimal sound transfer. © 2011 American Institute of Physics.