Impedances of Cochlear Implant Electrodes

Objective: The current study investigateswhether, during a Cochlear Implant (CI) surgery, conditioning(i.e. applying short bursts of electrical stimulation)within a saline solution can have positive effects on subsequentintra-operative measurements. We hypothesize that,based on previous research, the impedance values will bereduced, and that the reproducibility of Electrically EvokedCompound Action Potentials (ECAPs) is improved as aresult of conditioning.Methods: We conditioned half of the electrode contacts,within a saline solution, before CI insertion, using 23 MEDELimplants. Impedance was measured for both the conditionedand non-conditioned groups at five time points.Repeated ECAP recordings were measured and comparedbetween the conditioned and non-conditioned groups.Results: Impedance of the electrode contacts were reducedby 31% after conditioning in saline solution; however,there were no clinically relevant differences afterthe implantation of the electrode array. The hypothesisthat measurement reproducibility would be increased afterconditioning could not be confirmed with our data.Within the saline solution, we observed that 44% of theelectrode contacts were covered with air bubbles, whichmost disappeared after implantation. However, these airbubbles limited the effectiveness of the conditioning withinthe saline solution. Lastly, the effect of conditioning on thereference electrode stimulation was approximately 16% ofthe total reduction in impedance.Conclusion: Our data does not suggest that intraoperativeconditioning is clinically required for cochlear implantationwith MED-EL implants. Additionally, an in-vivo ECAPrecording can be considered as a method of conditioningthe electrode contacts.Significance: We confirm that the common clinical practicedoes not need to be changed.