From nucleus 24 to 513: changing cochlear implant design affects auditory response thresholds.

OBJECTIVES: We asked how thresholds of auditory activity evoked by a recent research cochlear implant, the Nucleus 513, compared with those evoked by previous generations of devices from the same manufacturer. STUDY
DESIGN: Prospective repeated measures.
SETTING: Tertiary pediatric hospital. PATIENTS: A total of 182 children receiving unilateral or bilateral Nucleus cochlear implants.
INTERVENTIONS: Of 182 children, 39 received the N24M straight array, the oldest device in this study, 20 received the N24RCS Contour, the next device released, 57 received the 24RE Freedom, released after the N24RCS, and 66 received the N513 Leap electrode array, the newest device. MAIN OUTCOME MEASURES: Behavioral thresholds and auditory nerve response thresholds were evoked by an apical, mid-array, and basal electrode and measured in 203 ears.
RESULTS: In general, auditory nerve thresholds decreased with newer devices. Responses evoked by the mid-array electrode had higher thresholds than responses to the other electrodes in most devices and highest in the operating room for the N513. Apical electrodes evoked the lowest thresholds at the level of the auditory nerve. Auditory nerve response thresholds decreased from the operating room to initial device activation with the 2 newest devices (N24RE and N513) tending to show the largest changes. Behavioral thresholds were at lowest levels for the 2 newest devices studied and, unlike auditory nerve response thresholds, decreased with age for all devices.
CONCLUSION: Evolving cochlear implant electrode design significantly affects auditory thresholds, but these changes do not occur uniformly along the array.