Effect of Probe-Tone Frequency on Ipsilateral and Contralateral Electrical Stapedius Reflex Measurement in Children With Cochlear Implants

Abstract

Objectives: The upper loudness limit of electrical stimulation in cochlear implant patients is sometimes set using electrically elicited stapedius reflex thresholds (eSRTs), especially in children for whom reporting skills may be limited. In unilateral cochlear implant patients, eSRT levels are measured typically in the contralateral unimplanted ear because the ability to measure eSRTs in the implanted ear is likely to be limited due to the cochlear implant surgery and consequential changes in middle ear dynamics. This practice is particularly limiting in the case of fitting bilaterally implanted pediatric cases because there is no unimplanted ear option to choose for eSRT measurement. The goal of this study was to identify an improved measurement protocol to increase the success of eSRT measurement in ipsilateral or contralateral or both implanted ears of pediatric cochlear implant recipients. This work hypothesizes that use of a higher probe frequency (e.g., 1000 Hz compared with the 226 Hz standard), which is closer to the mechanical middle ear resonant frequency, may be more effective in measuring middle ear muscle contraction in either ear. Design: In the present study, eSRTs were measured using multiple probe frequencies (226, 678, and 1000 Hz) in the ipsilateral and contralateral ears of 19 children with unilateral Advanced Bionics (AB) cochlear implants (mean age = 8.6 years, SD = 2.29). An integrated middle ear analyzer designed by AB was used to elicit and detect stapedius reflexes and assign eSRT levels. In the integrated middle ear analyzer system, an Interacoustics Titan middle ear analyzer was used to perform middle ear measurements in synchrony with research software running on an AB Neptune speech processor, which controlled the delivery of electrical pulse trains at varying levels to the test subject. Changes in middle ear acoustic admittance following an electrical pulse train stimulus indicated the occurrence of an electrically elicited stapedius reflex. Results: Of the 19 ears tested, ipsilateral eSRTs were successfully measured in 3 (16%), 4 (21%), and 7 (37%) ears using probe tones of 226, 678, and 1000 Hz, respectively. Contralateral eSRT levels were measured in 11 (58%), 13 (68%), and 13 (68%) ears using the three different probe frequencies, respectively. A significant difference was found in the incidence of successful eSRT measurement as a function of probe frequency in the ipsilateral ears with the greatest pair-wise difference between the 226 and 1000 Hz probe. A significant increase in contralateral eSRT measurement success as a function of probe frequency was not found. These findings are consistent with the idea that changes in middle ear mechanics, secondary to cochlear implant surgery, may interfere with the detection of stapedius muscle contraction in the ipsilateral middle ear. The best logistic, mixed-effects model of the occurrence of successful eSRT measures included ear of measurement and probe frequency as significant fixed effects. No significant differences in average eSRT levels were observed across ipsilateral and contralateral measurements or as a function of probe frequency. Conclusion: Typically, measurement of stapedius reflexes is less successful in the implanted ears of cochlear implant recipients compared with measurements in the contralateral, unimplanted ear. The ability to measure eSRT levels ipsilaterally can be improved by using a higher probe frequency.

Evaluation of the Electrically-Evoked Stapedial Reflex Threshold in Pediatric Cochlear Implant Users with High-Frequency Probe Tones

“…The incidence of successful ESRT measurements in the present study was slightly higher than that of other studies. 3 12 16 The higher incidence of the measurable ESRTs in the present study could be because all the participants had normal tympanogram findings and individual electrode stimulation during ESRT measurements in the present study. The individual electrode stimulation enabled the presentation of higher CLs before reaching an uncomfortable level for the participants.…”

“…The use of higher-frequency probe tones increases the success rate of ESRT measurements. In the study by Carranco Hernandez et al, 12 the success rates of ESRT measurements in children were of 58%, 68%, 68% for 226 Hz, 678 Hz, and 1,000 Hz respectively, when measured in contralateral non-implanted ears. In adult participants, Wolfe et al 11 reported that 13 out of 13 showed measurable ESRTs with 678 Hz or 1,000 Hz, and 12 out of 13 (92.3%), with 226 Hz.…”

“…This may be due to the relatively small sample size compared with that of other studies. 11 12 Wolfe et al 11 measured the ESRT with 226 Hz, 678 Hz, and 1,000 Hz in 23 adults using Advanced Bionics (Stäfa, Switzerland) implants. The authors 11 reported that the use of higher probe-tone frequencies (of 678 Hz or 1,000 Hz) resulted in ESRT levels that were 11 to 12.5 clinical units lower when compared with the default frequency of 226 Hz.…”

“…All of the 23 participants in this study 11 had measurable ESRTs with higher probe tone frequencies, whereas, at 226 Hz, 17 out of 23 (73.9%) participants had measurable ESRTs. Similarly, Carranco Hernandez et al 12 evaluated the effect of probe-tone frequency on ESRT measurements in ipsilateral and contralateral ears of 19 pediatric users of the Advanced Bionics HiRes 90 K CI. The ipsilateral ESRT was measured in 3 (16%), 4 (21%), and 7 (37%) ears, and the contralateral ESRT, in 11 (58%), 13 (68%), and 13 (68%) ears for 226 Hz, 678 Hz, and 1,000 Hz respectively.…”

“…Wolfe et al 11 reported that the use of higher-frequency probe tones (of 678 Hz or 1,000 Hz) resulted in lower ESRT levels than those obtained with 226 Hz in adult CI users. In a similar study in PCI users, Carranco Hernandez et al 12 reported that a higher probe tone could increase the successful measurement of the ESRT, especially in ipsilateral ears.…”