Investigation of Electrical Stimulation Levels Over 8 to 10 Years Postimplantation for a Large Cohort of Adults Using Cochlear Implants.

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.

The Change in Electrical Stimulation Levels During 24 Months Postimplantation for a Large Cohort of Adults Using the Nucleus® Cochlear Implant.

OBJECTIVES: To examine electrical stimulation data over 24 months postimplantation in adult implant users. The first aim was to calculate mean T and C levels for seven time points, for four cochlear segments, and two array types. The second aim was to (a) analyze the degree of change in each of the T and C levels as a function of dynamic range for six consecutive time point comparisons, for the four segments, and (b) to determine the proportion of participants with an acceptable degree of change. The third aim was to examine relationships between demographic factors and degree of change. DESIGN: T levels, C levels, and dynamic ranges were extracted for 680 adults using Nucleus implants for the following postimplant time points: 2-, 3-, 6-, 9-, 12-, 18-, and 24-month. For each time point, mean levels were calculated for the four segments. The degree of change in each of the levels was analyzed for six consecutive time point comparisons. The criterion for an acceptable degree of change was ≤20% of DR. RESULTS: Mean T level was significantly lower for the 2-month time point compared with all time points after the 3-month time point. Mean C level was significantly lower for the 2- and 3-month time points compared with all other time points. Mean T level was significantly lower for the apical compared with all other segments and for the lower-basal compared with the upper-basal segment. Mean C level was significantly different across all four segments. Mean C level for the basal segments was 4 CLs higher for the perimodiolar array compared with the straight array. No significant differences were evident for the mean degree of change between consecutive time point comparisons. For all segments, approximately 65 to 75% of the participants showed an average acceptable degree of change in levels from the 3- to 6-month comparison. The mean degree of change in T levels was significantly greater for the basal segments compared with all other segments. The mean degree of change in levels was significantly greater for the otosclerosis group compared with all other groups, and for the prelingual onset of deafness group compared with the postlingual group. CONCLUSION: Given the very large cohort, this study provides evidence for the mean levels and the degree of change in these levels that should be expected for four segments in the first 24 months postimplantation for adults using Nucleus implants. The mean T and C levels were consistent after the 3- and 6-month time points postimplant, respectively. The degree of change was variable between individuals. For each segment, however, a large percentage of participants showed an average change of ≤20% in each of the T and C levels from the 3- to 6-month comparison. Given the large degree of change in levels for some groups, the results provide strong evidence in favor of frequent monitoring of levels in the first 24 months postimplantation for patients with otosclerosis, prelingual onset of deafness, and those who exhibit >20% change in levels after 3 months postimplantation.