Electrically Evoked Stapedial Reflex in Cochlear Implantation / 대한이비인후과학회지

ABSTRACT

BACKGROUND AND OBJECTIVES: An essential part of the successful application of a cochlear implant is to adjust the stimulation levels to the patient's dynamic range. To test the subjective behavioral threshold (T-level) and the most comfortable loudness level (C-level), however, it may be troublesome or even impossible in very young children who are not able to perform such tasks appropriately. Therefore, utilization of objective measurements is important in children to estimate T- and C-levels. One of the objective measurements is the electrically evoked stapedial reflex (ESR) test. It has also been suggested that ESR may have applicability in confirming and quantifying electrical stimulation through a cochlear implant. The purpose of this study is to examine the feasibility of utilizing ESR to test device function during cochlear implant surgery and to predict ultimate behavioral T- & C-levels. MATERIALS AND METHODS: The ESR measurements were performed in 18 subjects during a cochlear implant surgery. Eight subjects received the Nucleus 22 multichannel cochlear implant (CI 22M) and 10 subjects received Nucleus 24 multichannel cochlear implant system (CI 24M). To test the ESRs, three electrodes, namely, apical electrode (E20), medial electrode (E12) and basal electrode (E5), were stimulated in each case. ESR thresholds were measured by visual observation of the stapedius muscle contraction in response to electrical stimulation delivered to the auditory nerve via a cochlear implant system. And the ESR thresholds were compared with the behavioral T- and C-levels in each electrode. RESULTS: ESRs were presented in 19/23 electrodes (82.6%) in subjects who received the CI 22M and 26/30 electrodes (86.7%) in subjects with CI 24M. The mean ESR threshold was the lowest in apical electrodes (E20) in both groups. In subjects with CI 22M, ESR thresholds were significantly correlated with behavioral T- and C-levels in apical electrodes (E20). In subjects with CI 24M, ESR thresholds were highly correlated with the C-levels in E5, E12, and E20. CONCLUSION: ESR provides an objective, accurate and rapid method to evaluate the device function during cochlear implant surgeries and in estimating T-/C- levels, which may be useful in the initial programming of younger children and the difficult-to-tests.