Optimizations for the Electrically-Evoked Stapedial Reflex Threshold Measurement in Cochlear Implant Recipients

Objective: The electrically-evoked stapedial reflex threshold (eSRT) has proven to be useful in setting upper stimulation levels of cochlear implant recipients. However, the literature suggests that the reflex can be difficult to observe in a significant percentage of the population. The primary goal of this investigation was to assess the difference in eSRT levels obtained with alternative acoustic admittance probe tone frequencies. Design: A repeated-measures design was used to examine the effect of 3 probe tone frequencies (226, 678, and 1000 Hz) on eSRT in 23 adults with cochlear implants. Results: The mean eSRT measured using the conventional probe tone of 226 Hz was significantly higher than the mean eSRT measured with use of 678 and 1000 Hz probe tones. The mean eSRT were 174, 167, and 165 charge units with use of 226, 678, and 1000 Hz probe tones, respectively. There was not a statistically significant difference between the average eSRTs for probe tones 678 and 1000 Hz. Twenty of 23 participants had eSRT at lower charge unit levels with use of either a 678 or 1000 Hz probe tone when compared with the 226 Hz probe tone. Two participants had eSRT measured with 678 or 1000 Hz probe tones that were equal in level to the eSRT measured with a 226 Hz probe tone. Only 1 participant had an eSRT that was obtained at a lower charge unit level with a 226 Hz probe tone relative to the eSRT obtained with a 678 and 1000 Hz probe tone. Conclusions: The results of this investigation demonstrate that the use of a standard 226 Hz probe tone is not ideal for measurement of the eSRT. The use of higher probe tone frequencies (i.e., 678 or 1000 Hz) resulted in lower eSRT levels when compared with the eSRT levels obtained with use of a 226 probe tone. In addition, 4 of the 23 participants included in this study did not have a measureable eSRT with use of a 226 Hz probe tone, but all of the participants had measureable eSRT with use of both the 678 and 1000 Hz probe tones. Additional work is required to understand the clinical implication of these changes in the context of cochlear implant programming.

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