Abstract
PURPOSE: Several therapeutic approaches for hearing disorders involve attaching medical devices to the tympanic membrane. The attachment of these devices can change the mechanical and acoustical properties of the middle ear, affecting the middle-ear vibrations. The alteration of passive mechanical properties results from the mass, stiffness, and geometry of the attached device. Additionally, procedures like tympanostomy tube attachment create perforations on the tympanic membrane, altering both the mechanical and acoustical properties of the middle ear. This study examined the acoustical effects of these as well as the combination of acoustical and mechanical effects of the attached devices on middle-ear vibrations. METHODS: A finite-element model of the middle ear, including the middle-ear cavity, was used to systematically study the effects of perforation size and location on vibration outputs. Experimental data from the literature were used to tune the model. This model was then employed to investigate the combined mechanical and acoustical effects of tympanostomy tubes on vibration outputs. RESULTS: In presence of both the mechanical effects of the device (due to its mass and stiffness) and the acoustical effects of it (due to perforations), the reduction in the motion of the stapes footplate resulting from the acoustical effects is more remarkable at low frequencies (below about 1 kHz). However, at higher frequencies, the mechanical effects of the device are dominant. CONCLUSION: The findings of this study provide insights into the optimal design of the shape, location, and other characteristics of medical devices implanted on the tympanic membrane.