[Correlation between electrically-induced stapedius reflex and discomfort threshold in cochlear implant patients]

Electrically elicited stapedius reflex thresholds are an objective criteria for the fitting of speech processors in very young children. Reflex thresholds generally fit well within the upper third of a subject's individual dynamic range, the difference between electrical threshold of hearing, (T) and maximum comfort (C) levels and can be used to predict ultimate behavioral maximum comfort levels. In acoustically elicited stapedius reflexes a saturation of impedance amplitude can be registered at approximately 110 dB, which is 90% of the dynamic range. Assuming a similar relationship for the electrically elicited stapedius reflex there would be two values within the dynamic range which could be used for extrapolation of the threshold level. In the present study, the electrically elicited stapedius reflex was examined in 16 deaf patients who had received 22-channel Clark/NUCLEUS cochlear implants. Using an apical, a medial and a basal electrode pair, different stimulation positions within the cochlea were tested. The contralateral reflexes could be elicited in 11 patients (69%). A saturation of the reflex amplitude was recordable in 10 subjects, at least in one of the electrode pairs. The reflex saturation in all cases was located close to the uncomfortable loudness level within the subjects' dynamic ranges (at 95% dynamic). This finding is comparable to acoustic matter. As a result, these data together with reflex threshold data suggest a means for predicting to predict the threshold levels.