Prediction of mechanical effect due to a cochlear implant

The effect of a cochlear implant on residual, low frequency, hearing is complex and poorly understood. This research focuses on the mechanical effect of a cochlear implant on the cochlear mechanics by comparing the predicted basilar membrane, BM, response before and after the implantation. Audiograms measured from pre- and post-implant users are used as input of a computational model of the passive cochlea, proposed by Elliott et al. (Elliott et al., 2011), which are then used to study the mechanical effect of the implantation. In the model, a short cochlea implant, designed to electrically stimulate the basal regions at high frequencies while allowing normal hearing at low frequencies (Cochlear, 2008), is introduced into the lower cochlear fluid chamber. The active amplification of the cochlea is not considered, since a passive cochlear model whose response is not dependent on stimulus level can reasonably well represent the cochlea for subjects with hearing impairment. The results for the BM coupled response show that the volume change in the fluid chambers due to the implant has a negligible effect, less than about 0.1 dB, on the vibration of the modeled cochlea at low frequencies. A more extreme condition, in which the cochlear implant is assumed to touch the BM at some or whole basal positions and thus impeded its motion, is also studied. Although no travelling wave can propagate in the basal region in the latter case, the remainder of the cochlea is still coupled to the stapes by incompressible fluid. The BM response at low frequencies is relatively unaffected by the blocking of the BM motion in the basal region, although the effect is more dramatic for excitation frequency whose characteristic place is close to the end of the implant. Although this work does not model every aspect of the cochlear implantation, it does provide a way of predicting the possible mechanical effects of the implantation on the cochlear passive mechanics and the residual hearing