12/13/2022 0 Comments Scala vestibuli![]() ![]() The influence of the implantation of transversely isotropic mechanical models was also studied, by comparing the basilar membrane with isotropic and transversely isotropic mechanical properties. The present numerical study highlights the distinctions of using a spiral model of the cochlea, by comparing the obtained results with a straight, or simplified model. Existing mathematical and numerical models available in the literature try to describe the shape of this travelling wave, the majority of them present a set of approaches based on some limitations either or both of the mechanical properties used and the geometrical description of the realistic representation. At present, it is known that during an acoustic stimulation a travelling wave is developed inside the cochlea. Hearing impairment is one of the most common health disorders, affecting individuals of all ages, reducing considerably their quality of life. High frequencies, however, should not be amplified in patients using EAS to avoid disturbances in discrimination due to tonotopically incorrect frequency representation. Observations in implanted subjects were concordant with our model predictions. Focussing of acoustic energy may increase perception in regions adjacent to the fixed section. Our model suggests that stiffening of the basilar membrane adjacent to an implanted electrode into the basal and middle cochlear turn did not affect BM movement in the low frequency area. In implanted subjects, a small but significant decrease of thresholds was observed at 1.5 kHz, a place in tonotopy adjacent to the tip region of the implanted electrode. Lower frequencies were not affected by fixation in the basal and middle turn of the cochlea. In the scenario of partial BM-fixation, acoustic energy of middle (2 kHz) and high (6 kHz) frequency was focused basally and apically to the fixed section, increasing BM displacement amplitudes up to 6 dB at a stimulation level of 94 dB (SPL). To verify our simulated results, pre- and postoperative pure-tone audiograms of 13 subjects with substantial residual hearing, who underwent cochlear implantation, were evaluated. Intracochlear introduction of a cochlear implant electrode, however, may alter the biomechanical properties of the inner ear and thus affect perception of acoustic stimuli.īased on histological observations of morphologic changes after cochlear implantation in cadaveric and post mortem studies the effects of basilar membrane (BM) stiffening in the ascending basal and middle turns of the cochlea due to close contact of the BM with the electrode were simulated in a 3D-computational finite element model of the inner ear. In subjects with remaining low frequency hearing, combined electric-acoustic stimulation (EAS) of the auditory system is a new therapeutic perspective. Although a unique lumped parameter network cannot be inferred from such a pole-zero description, these fitted results help indicate what properties such a network should have. The model with the best overall fit to the data is found to be one with two degree-of-freedom micromechanics and 3D fluid coupling. A model with two degree-of-freedom micromechanics generally fits the measurements better than a model with single degree-of-freedom micromechanics, particularly at low excitations where the cochlea is active, except post-mortem conditions, when the cochlea is passive. These elements are then used in a model of the coupled cochlea, which is optimised to minimise the mean square difference between its frequency response and that measured on the basilar membrane inside the mouse cochlea by Lee, Raphael, Xia, Kim, Grillet, Applegate, Ellerbee Bowden, and Oghalai and Oghalai Lab, at different excitation levels. Pole-zero models with local scaling symmetry are derived for both one and two degree-of-freedom micromechanical systems. ![]() An efficient way of describing the linear micromechanical response of the cochlea is in terms of its poles and zeros. ![]()
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