Background and Objectives : An essential part of the successful application of a cochlear implant
is to adjust the stimulation levels to the patients 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-level. 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 tothe 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 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.
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