Impedance-based tissue response modeling for the prediction of hearing preservation after cochlear implantation

Cochlear implant (CI) patients increasingly retain residual acoustic hearing, which supports speech understanding if preserved after surgery. However, the immune reaction (i.e., tissue response) following implantation can result in delayed loss of residual hearing. Recent evidence established a link between CI electrode impedance and the tissue response, indicating its potential as a biomarker for cochlear health. This prospective study hypothesizes that postoperative impedance evolution can be described by a tissue response model, with the aim of predicting hearing preservation in CI patients. In 33 CI cases, we repeatedly recorded impedance and hearing preservation in a six-month follow-up. We characterized the impedance dynamics within two months, by fitting a biology-inspired, dynamical model of the tissue response. To evaluate the model's applicability, we compared the fitted parameters with hearing preservation until six months. Additionally, we examined the model's impedance predictions in the same period. Our results indicated that our model accurately reproduces the early impedance dynamics. Furthermore, we revealed a significant association between the dynamic parameter and hearing preservation at three (r=0.81,p<.001) and six months (r=0.66,p<.001) postoperatively. Meanwhile, the model underestimated longitudinal impedance (mean errors of -1.1kΩ at three, and -1.6kΩ at six months), likely because of fibrosis. We introduced a biology-inspired model of the tissue response in CI patients to characterize postoperative impedance dynamics and to predict hearing preservation. These findings can potentially help to assess cochlear health objectively in CI patients.