Stapedius reflex thresholds obtained in a free sound field as an indicator for over- and understimulation in cochlear implant listeners.

OBJECTIVE: The goal of this study was to determine open field stapedius reflex thresholds (oSRTs) in CI patients with fittings based on subjective loudness ratings. A further objective was to compare these oSRTs and those of eSRT-based fittings that are similar to the oSRTs of normal hearing. DESIGN: Impedance measurements of the ear drum were taken while subjects were wearing their audio processors. The stapedius reflex was elicited by electrical stimulation transmitted through the activated CI system in response to an acoustic stimulus presented in the free sound field. STUDY SAMPLE: Subjects were 50 experienced CI users (n = 57 ears) with CI fittings based on subjective loudness scaling. RESULTS: A reference range for the oSRTs was defined that was identified in CI patients with eSRT-based fittings. Sound levels for stapedius reflex detection were inside the reference target range in 70% of the cases, below the reference range (i.e. down to 40 dB HL) in 20% of the cases, and above the reference range in 10% of the cases. CONCLUSION: Stapedius reflex detection in a free sound field may help detect fittings with too high or too low stimulation levels that might reduce audiological performance.

Stapedius reflex evoked in free sound field in cochlear implant users compared to normal-hearing listeners.

OBJECTIVE: To determine the relation between stapedius reflex thresholds in cochlear implant users evoked once through direct electric stimulation on single channels (ESRT) and once through acoustic stimulation in free sound field. For comparison, stapedius reflex thresholds were obtained in free sound field in a normal-hearing control group. DESIGN: For each participant a new ESRT-based fitting was created. Stapedius reflex thresholds were obtained for this new fitting in free sound field for different loudness adjustments. Acoustic stimuli for eliciting the stapedius reflex were narrow band noise signals covering the audiometric frequency range. STUDY SAMPLE: N = 29 experienced CI users (34 ears) and N = 10 normal hearing listeners. RESULTS: ESRT-based fitting resulted in different stapedius reflex behaviour compared to normal-hearing listeners. A frequency dependence was observed. Stapedius reflex thresholds decreased with increasing centre frequencies of acoustic narrow band noise stimuli. A linear relation between upper stimulation levels on the implant channels and corresponding stapedius reflex thresholds evoked in free sound field was found. CONCLUSION: The found correlation may be a guideline for adjusting the electrical dynamic range during cochlear implant fitting. This allows the implant system to mimic the natural reflex behaviour in the best possible way and potentially avoid overstimulation.

Estimation of insertion depth angle based on cochlea diameter and linear insertion depth: a prediction tool for the CI422.

Beside the cochlear size, the linear insertion depth (LID) influences the insertion depth angle of cochlear implant electrode arrays. For the specific implant CI422 the recommended LID is not fixed but can vary continuously between 20 and 25 mm. In the current study, the influence of cochlea size and LID on the final insertion depth angle was investigated to develop a prediction tool for the insertion depth angle by means of cochlea diameter and LID. Preoperative estimation of insertion depth angles might help surgeons avoid exceeding an intended insertion depth, especially with respect to low-frequency residual hearing preservation. Postoperative, high-resolution 3D-radiographs provided by Flat Panel Computed Volume Tomography (FPCT) were used to investigate the insertion depth angle in 37 CI422 recipients. Furthermore, the FPCT images were used to measure linear insertion depth and diameter of the basal turn of the cochlea. A considerable variation of measured insertion depth angles ranging from 306° to 579° was identified. The measured linear insertion depth ranged from -18.6 to 26.2 mm and correlated positively with the insertion depth angle. The cochlea diameter ranged from 8.11 to 10.42 mm and correlated negatively with the insertion depth angle. The results suggest that preoperatively measured cochlea diameter combined with the option of different array positions by means of LID may act as predictors for the final insertion depth angle.

Word Recognition with a Cochlear Implant in Relation to Prediction and Electrode Position.

BACKGROUND: the word recognition score (WRS) achieved with cochlear implants (CIs) varies widely. To account for this, a predictive model was developed based on patients' age and their pre-operative WRS. This retrospective study aimed to find out whether the insertion depth of the nucleus lateral-wall electrode arrays contributes to the deviation of the CI-achieved WRS from the predicted WRS. MATERIALS AND METHODS: patients with a pre-operative maximum WRS > 0 or a pure-tone audiogram ≥80 dB were included. The insertion depth was determined via digital volume tomography. RESULTS: fifty-three patients met the inclusion criteria. The median WRS achieved with the CI was 70%. The comparison of pre- and post-operative scores achieved with a hearing aid and a CI respectively in the aided condition showed a median improvement of 65 percentage points (pp). A total of 90% of the patients improved by at least 20 pp. The majority of patients reached or exceeded the prediction, with a median absolute error of 11 pp. No significant correlation was found between the deviation from the predicted WRS and the insertion depth. CONCLUSIONS: our data support a previously published model for the prediction of the WRS after cochlear implantation. For the lateral-wall electrode arrays evaluated, the insertion depth did not influence the WRS with a CI.

Insertion depth angles of cochlear implant arrays with varying length: a temporal bone study.

HYPOTHESIS: The aim of the study is to investigate the insertion depth angles for different types of electrode arrays and its variability depending on the individual cochlear size. BACKGROUND: Preoperative estimation of the insertion depth angles for different electrode arrays can help surgeons choose the optimal electrode length, especially for low-frequency residual hearing preservation. METHODS: Four different electrode arrays varying in lengths (20, 24, 28, and 31 mm) were inserted in 10 temporal bones to quantify the insertion depth angle of each inserted electrode. High-resolution 3D radiographs provided by Flat Panel Computed Volume Tomography (FPCT) were used to determine electrode array insertion depth angle and diameter of the cochlea's basal turn. RESULTS: The high-resolution FPCT images from all electrode arrays inserted into the temporal bones allowed reliable measurements of insertion depth angles. In particular, statistically significant different insertion depth angles between the various array types were identified. The insertion of the 20-, 24-, 28-, and 31-mm arrays yielded a mean insertion depth angle of 341 degrees (SD, 22 degrees), 477 degrees (SD, 36 degrees), 587 degrees (SD, 42 degrees), and 673 degrees (SD, 38 degrees), respectively. Furthermore, a statistically significant negative correlation between insertion depth angle and diameter of the cochlea's basal turn was found for the 20- and 31-mm arrays. CONCLUSION: The results suggest an individually adapted length of electrode arrays, which should be taken into account for an improved decision paradigm for patients scheduled for cochlear implantation. This is of particular importance for patients with low-frequency residual hearing.