Investigation of Electrical Stimulation Levels Over 8 to 10 Years Postimplantation for a Large Cohort of Adults Using Cochlear Implants
Authors: Gajadeera Emalka A. , Galvin Karyn L. , Dowell Richard C. , Busby Peter A. 
Published: June 2017

Objectives:
This study examined electrical stimulation levels over 8 to 10 years postimplantation in adult Nucleus implant users. The first aim was to investigate long-term trends and amount of change in electrical stimulation levels for each of four electrode array segments. The second aim was to determine long-term trends and amount of change for particular participants who previously showed greater change (i.e., >20% of dynamic range [DR]) in each of the threshold (T) and comfort (C) levels within the first 3 to 6 months postimplantation. The third aim was to determine whether demographic characteristics were predictive of the long-term trends and amount of change in each of the T and C levels.

Design:
For 128 adults implanted with Nucleus implants, T levels, C levels, and DR were extracted for the following postimplant time points: 6, 9, 12, 18, 24, 48, 72, 96, and 120 months. For each time point, the mean T levels, C levels, and DR were calculated for each of four electrode array segments. For each participant, regression analyses were conducted for each of the levels and DR, separately for each of the four electrode array segments. Proportions of participants with and without statistically significant trends were identified, and the amount of change was determined for all participants.

Results:
No significant differences in trends and amount of change were evident across segments for either of the T or C levels. On average across the four segments, 42% of participants showed nonsignificant trends in each of the T and C levels; 24% and 18% of the participants showed a significant trend only in C levels or only in T levels, respectively. Only 16% of the participants showed a significant trend in both T and C levels. Separately, 73% of the participants showed a nonsignificant trend in DR. In terms of current levels (CLs), the mean amount of change over 10 years for all participants was 10.4 (SD = 8.2) and 10.8 (SD = 9.8) for T and C levels, respectively. For both T and C levels, approximately 95% of the participants showed <25 CLs of change over the 10 years. For both T and C levels, at least 75% of the participants showed less than 6% change each year as a function of their average DR across the 8 to 10 years. For the participants who were previously reported to show >20% change in levels as a function of DR in the first 3 to 6 months postimplantation, nonsignificant long-term trend in levels was shown for 70% of these participants over the first 8 to 10 years postimplantation. Etiology, onset of hearing loss, and age at implantation were not significant factors in predicting change in levels. Duration of hearing loss and hearing aid use before implantation were both predictive of long-term change in T and C levels, respectively. In terms of the amount of change in CLs, both these factors showed a very small amount of change in CLs.

Conclusions:
The majority of adults using Nucleus implants showed a nonsignificant trend in T levels, C levels, and DR over 8 to 10 years postimplantation. The present study provides strong evidence that only a small amount of change in levels should be expected for most adults from 6 months out to 10 years postimplantation. A large proportion of the subgroup of participants who previously showed more change in the first 3 to 6 months showed consistent long-term results with the overall group. The trends in levels and the amount of change in levels in the long term were not significantly associated with the demographic characteristics investigated. For implant users with consistent levels over a number of sessions after the first 6 months postimplantation, the frequency of programming in the long term can be reduced. The translation of the findings from the present study into clinical practice will enable more efficient programming services to be provided to implant users in the long term.