Population-Based Prediction of Fitting Levels for Individual Cochlear Implant Recipients

Abstract

Objectives: This study analyzed the predictability of fitting levels for cochlear implant recipients based on a review of the clinical levels of the recipients. Design: Data containing threshold levels (T-levels) and maximum comfort levels (M-levels) for 151 adult subjects using a CII/HiRes 90K cochlear implant with a HiFocus 1/1 J electrode were used. The 10th, 25th, 50th, 75th and 90th percentiles of the T- and M-levels are reported. Speech perception of the subjects, using a HiRes speech coding strategy, was measured during routine clinical follow-up. Results: T-levels for most subjects were between 20 and 35% of their M-levels and were rarely (<1/50) below 10% of the M-levels. Furthermore, both T- and M-levels showed an increase over the first year of follow-up. Interestingly, levels expressed in linear charge units showed a clear increase in dynamic range (DR) over 1 year (29.8 CU; SD 73.0), whereas the DR expressed in decibels remained stable. T-level and DR were the only fitting parameters for which a significant correlation with speech perception (r = 0.34, p < 0.01, and r = 0.33, p < 0.01, respectively) could be demonstrated. Additionally, analysis showed that T- and M-level profiles expressed in decibels were independent of the subjects' across-site mean levels. Using mixed linear models, predictive models were obtained for the T- and M-levels of all separate electrode contacts. Conclusions: On the basis of the data set from 151 subjects, clinically applicable predictive models for T- and M-levels have been obtained. Based on one psychophysical measurement and a population-based T- or M-level profile, individual recipients' T- and M-levels can be approximated with a closed-set formula. Additionally, the analyzed fitting level data can serve as a reference for future patients. i 2014 S. Karger AG, Basel

Intracochlear Position of Cochlear Implants Determined Using CT Scanning versus Fitting Levels: Higher Threshold Levels at Basal Turn

“…Due to the preset profile used to determine the M-levels used in our clinic, no further conclusion from either M-levels or DR could be drawn from this study. Moreover, only the T-levels, in contrast to the M-levels, show a firm correlation with the degree of speech perception [van der Beek et al, 2015], and most of the correlations described in the present study were discovered using the T-levels.…”

“…Clinical research has shown a correlation between the DR and speech perception that endorses the need for setting the proper fitting levels for cochlear implants [Blamey et al, 1992;Pfingst and Xu, 2005;Pfingst et al, 2004;van der Beek et al, 2015]. The aim of the present study was to determine whether radiological data provided additional information for setting the speech processor map levels.…”

“…3 ), and whether the additional knowledge obtained from a radiological analysis would help with fitting the patient was considered. A previous study [van der Beek et al, 2015] showed that T-levels could be fitted by determining the T-level at one electrode contact and applying a closed-set formula for the T-level profile based on group data. Adding radiological data to such a model might further increase the applicability of this approach for clinical programming.…”

“…Figure 6 shows that the insertion depth of the array significantly affected the T-level profile. This effect was further analyzed by adding the insertion depth to the population-based predictive formula for the levels [van der Beek et al, 2015]. Although this process yielded a significant parameter, it did not increase the predictability of the levels (data not shown).…”

“…Previous studies have demonstrated that there is a certain level of conformity in the M-and T-level profiles, both of which tend to increase toward the basal end of the cochlea [Smoorenburg, 2007]. This increase has been observed for cochlear implants produced by different manufacturers (Cochlear Corp., Lane Cove, Australia; Advanced Bionics, Sylmar, Calif., USA; MedEl Corp., Innsbruck, Austria) [Baudhuin et al, 2012;Botros and Psarros, 2010;Cafarelli et al, 2005;D'Elia et al, 2012;Lai et al, 2009;Miller et al, 2008;Polak et al, 2005;Smoorenburg et al, 2002;Thai-Van et al, 2001;van der Beek et al, 2015;Vargas et al, 2013]. Furthermore, both perimodiolar and more lateral electrodes (Nucleus Straight vs. Contour) show higher levels basally [Polak et al, 2004].…”