Objective measures with the Nucleus® CI532 cochlear implant.

Objective: We explored the impact that basal medial-lateral electrode position had on threshold (T) and comfortable (C) levels and ECAP thresholds (T-NRT): Medial-lateral position as measured by wrapping factor (WP) indicated that the array was generally positioned close to the modiolus (mean WP=0.62, S.D. 0.05). There was however quite some variation in medial-lateral position of electrodes within the first 180° of the basal turn; mainly dependent on the number of markers inserted in the cochlea opening. Method: Basal medial-lateral position was categorized into "poor", "moderate" and "good" indicating some lateral wall contact, mid-scala position or perimodiolar position. Electro-physiological data and psycho-physical levels were analysed by electrode position group. Results: Across the three groups ECAP thresholds were higher for basal electrode contacts compared to apical ones with ECAP thresholds being consistently low across the three groups for apical electrode contacts. However there were differences in ECAP thresholds between groups for basal electrodes with ECAP thresholds for the "poor", laterally- positioned basal electrode contacts being higher than for the other two groups. A similar trend was seen for T and C levels. Longitudinal ECAP data for a smaller group of patients indicated that ECAP thresholds generally reduced over time; by approximately 20 current level units. Conclusions: ECAP thresholds varied across the electrode array for patients implanted with Nucleus CI532. ECAP thresholds for basal electrode contacts varied according to medial-lateral position, however ECAP thresholds were consistently low for apical electrode contacts. These results reinforce the importance of inserting only to the first position marker of the CI532 to ensure the best perimodiolar position and lowest stimulation levels. However levels generally reduced over time and fitting methods based on objective ECAP threshold measures are compatible with the CI532. [ABSTRACT FROM AUTHOR]