The Electrical Stability of The Electrodes in Long-term Cochlear Implant Patients

Abstract

We investigated the electrical stability of electrodes in long-term cochlear implant patients and the effects on the cochlear nerve. The function of the electrode array was studied using the minimal threshold level (T-level), the maximum comfortable level (C-level), and the dynamic range between T-and C-level (DR).
The percentage of the electrodes in use decreased within 1 year after the initialization but was stabilized after that, and kept 89% for 4 years after the initialization. The electrodes became out of use mainly because of facial palsy and uncomfortable sensation, which was claimed mostly near the round window. The averaged fluctuation of T-level, C-level, and DR of each electrode became stable 1 year after the initialization and was within 25μA 4 years after in 10 cases in which all electrodes were in use for more than 4 years. The electrodes near the round window fluctuated largely. These results suggested that the surgical trauma brought the effect on the electrodes near the round window stepwise. The electrode showed stable response in one case 10 years after the initialization. We concluded the effect of long-term electrical stimulation under the allowed value on the cochlear nerve was not so much as to effect the ability of hearing.