Development and Implementation of a Methodology for Determining Stimulation Threshold Current during Neural Response Telemetry of Cochlear Implant Users

Introduction. In cochlear implant systems, automatic algorithms that include neural response telemetry are not always capable of determining the threshold stimulation current that generates an electrically evoked compound action potential with minimum amplitude on intracochlear electrodes. The target current can be determined by the linear regression method based on the data obtained during telemetry. However, this method does not consider the physiological characteristics of the human auditory system. Aim. Development of a methodology for determining the threshold stimulation current and its implementation in clinical practice, considering the actual physiological nonlinear dependence of the amplitudes of the electrically   evoked potential of the auditory nerve on the stimulation current in cochlear implant users. Materials and methods. Three users of cochlear implant systems were involved. In each of them, it was impossible to conduct neural response telemetry using automated algorithms due to failure of the extracochlear electrode (while maintaining the clinical effect of the implant), lack of a technical сapability to support the automated algorithm (an early model implant), and meningitis with subsequent obliteration of the cochlea. An advanced (compared to the automated algorithm)   telemetry was conducted for each user, performed post-operatively in two users and intraoperatively in one of them. Results. The proposed methodology involves the formation of the growth function of the amplitude of the electrically evoked action potential of the auditory nerve depending on the equivalent stimulation current, finding the first point of the telemetry of the nerve response with a coordinate (equivalent stimulation current, amplitude); finding the zero point corresponding to the maximum value of the current equivalent that does not generate a potential; determining the threshold equivalent current as the average value of the zero and first points. In total, threshold currents on 32 electrodes (for three users) were determined using the proposed methodology and the linear regression method. Conclusion. The methodology can be used in case of failure of the automated algorithm both intra- and postoperatively, thus enhancing the quality of medical care provided to the users of cochlear implant systems.

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