Comprehensive decomposition of cochlear implant electrode impedances

Impedance telemetry is a routine procedure in cochlear implant care, providing insights into the electrode-tissue interface. Analyzing its electrical characteristics helps assess patient outcomes by accounting for implant-specific and tissue-related factors. This work introduces a method to estimate the electrical components of an impedance model for a detailed characterization of electrode impedances. Our approach relies on clinical software, requiring no modifications to standard measurement protocols. A mathematical model describing the total impedance as a function of the pulse duration was introduced. By fitting it to impedance recordings with varying pulse durations, the Warburg capacitance and Faradaic resistance were estimated. The current return path was modeled as a non-leaky resistive transmission line, and its individual resistances were calculated from the voltage matrix. Results were compared to an established geometric approach for estimating near-field and far-field impedance subcomponents. We observed a strong agreement between the geometric method and the proposed approach, indicated by a mean difference of 155Ω (near-field) and -107Ω (far-field) and a relative mean error of 4% and 18% respectively. The evolution of the electrical components over time is consistent with previous studies and may serve as a valuable tool for characterizing and monitoring the dynamic behavior of the electrode-electrolyte. The proposed method offers a robust decomposition of the electrode impedance model and can be seamlessly integrated into clinical practice using standard software. It provides features for applications such as estimating electrode array insertion depth, assessing residual hearing, and monitoring tissue responses, thus supporting clinical decision-making and further research.