Toward a method for programming balanced bilateral cochlear implant stimulation levels in children

In the present study, we investigated differences in stimulation levels between bilateral cochlear implants (CIs) in children and compared these to previously recorded measures of balanced input. We hypothesized that differences in stimulation levels between two CI: (1) will be observed both in behavioral and objective measures, and (2) can help to provide bilateral stimulation levels that are perceived as balanced.

Participants were 19 children who received bilateral CIs sequentially. Behaviorally determined minimum and maximum stimulation levels from the first (CI-1) and second (CI-2) CIs at an apical electrode (#20) were compared with thresholds of the electrically evoked compound action potential (ECAP) of the auditory nerve and electrically evoked stapedius reflex (ESR).

All four measures were found to be greater when evoked from CI-1 than CI-2 and the dynamic range between behavioral measures was reduced in CI-2 relative to CI-1. Significant correlations were found between differences in behavioral and objective measures; as differences in T-levels between CI-1 and CI-2 increased, so did the differences in ECAP thresholds and a similarly positive relationship was found between C-level differences and ESR threshold differences. Differences in ECAP thresholds between CI-1 and CI-2 were significantly correlated with balanced bilateral levels.

Children using two different Nucleus CIs often require different stimulation levels on either side. Although lower levels were needed on the side more recently implanted with newer technology, the dynamic range of input provided on the second side was reduced relative to the more experienced side. Differences in behavioral measures between CI-1 and CI-2 can be partially predicted by objective measures. ECAP thresholds show the best promise for helping to provide balanced bilateral CI input in children.