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.

Prediction of behavioral MCL using electrophysiological responses in children using MED-EL implant

The present study aimed to correlate the various electrophysiological tests of ECAP, EABR and ESRT with programming parameters. If there is a correlation between them, fitting formulae to be derived to predict programming parameters. Further this fitting formula was validated on a clinical population. 22 children between age range of 5-12 years using MED-EL implant participated study. Electrophysiological tests of Electrically evoked compound Action Potential (ECAP), Electrical Evoked Stapedial Reflex Threshold (ESRT) and Electrically Evoked Auditory Brain Stem Responses (EABR) were measured on electrodes no 1,4, 8, and 11. Based on Pearson correlation analysis, there was a moderate correlation observed between each of electrophysiological tests with MCL level. Fitting formulae of ECAP with either ESRT or EABR were found to be accurately predict the MCL level. These fitting formulae were clinically validated on 6 children using Sonata implant with OPUS 2 processor. Two new programs with MCL were predicted using combination of ECAP with EABR and ECAP with ESRT as parameters in the fitting formulae. These programs were given to the participants to use for two weeks. Predicted MCLs were found to slightly higher (about 2qu to 5qu) than original MCL level. Reliability analysis indicated that the formulae predicted MCL with good accuracy. Speech perception and sound field thresholds were measured in the participants' Everyday program and two predicted programs. When ECAP & EABR were the parameters, the predicted program had improved audibility as reflected in sound field thresholds as compared to those obtained with other two programs. Based on Freidman test, the results indicated that significantly lower thresholds were found for both ECAP & EABR, or ECAP & ESRT based programs when compared to Everyday program. However, speech perception scores were not significantly different among the program as per Freidman test. Thus, both the fitting models were clinically validated. The findings imply that it is not always advisable to run all three electrophysiological testing to predict the MCL levels in clinical population. It would save lot of time to run just two tests to predict the MCL in difficult to test population.

Relationship between electrically evoked compound action potential thresholds and behavioral T-levels in implanted children with cochlear nerve deficiency

It is challenging to program children with cochlear nerve deficiency (CND) due to limited auditory and speech abilities or concurrent neurological deficits. Electrically evoked compound action potential (ECAP) thresholds have been widely used by many audiologists to help cochlear implant programming for children who cannot cooperate with behavioral testing. However, the relationship between ECAP thresholds and behavioral levels of cochlear nerve in children with CND remains unclear. This study aimed to investigate how well ECAP thresholds are related to behavioral thresholds in the MAP for children with CND. This study included 29 children with CND who underwent cochlear implantation. For each participant, ECAP thresholds and behavioral T-levels were measured at three electrode locations across the electrode array post-activation. The relationship between ECAP thresholds and behavioral T-levels was analyzed using Pearson's correlation coefficient. The results showed that ECAP thresholds were significantly correlated with behavioral T-levels at the basal, middle, and apical electrodes. ECAP thresholds were equal to or higher than the behavioral T-levels for all tested electrodes, and fell within MAP's dynamic range for approximately 90% of the tested electrodes. Moreover, the contour of the ECAP thresholds was similar to the contour of T-levels across electrodes for most participants. ECAP thresholds can help audiologists select stimulation levels more efficiently for children with CND who cannot provide sufficient behavioral response.

ARTFit—A Quick and Reliable Tool for Performing Initial Fittings in Users of MED-EL Cochlear Implants

This study assessed the safety and performance of ARTFit, a new tool embedded in MAESTRO, the cochlear implant (CI) system software by MED-EL GmbH (Innsbruck, Austria). ARTFit automatically measures thresholds of the electrically evoked compound action potential (ECAP) to produce initial ‘maps’ (ECAPMAPs), i.e., configuration settings of the audio processor that the audiologist switches to live mode and adjusts for comfortable loudness (LiveECAPMAPs). Twenty-three adult and ten pediatric users of MED-EL CIs participated. The LiveECAPMAPs were compared to behavioral maps (LiveBurstMAPs) and to the participants’ everyday clinical maps (ClinMAPs). Four evaluation measures were considered: average deviations of the maximum comfortable loudness (MCL) levels of the LiveECAPMAPs and the LiveBurstMAPs from the MCLs of the ClinMAPs; correlations between the MCLs of the LiveECAPMAPs (MCL_ecap) and the LiveBurstMAPs (MCL_burst) with the MCLs of the ClinMAPs (MCL_clin); fitting durations; and speech reception thresholds (SRTs). All evaluation measures were analyzed separately in the adult and pediatric subgroups. For all evaluation measures, the deviations of the LiveECAPMAPs from the ClinMAPs were not larger than those of the LiveBurstMAPs from the ClinMAPs. The Pearson correlation between the MCL_ecap and the MCL_clin across all channels was r² = 0.732 (p < 0.001) in the adult and r² = 0.616 (p < 0.001) in the pediatric subgroups. The mean fitting duration in minutes for the LiveECAPMAPs was significantly shorter than for that of the LiveBurstMAPs in both subgroups: adults took 5.70 (range 1.90–11.98) vs. 9.27 (6.83–14.72) min; children took 3.03 (1.97–4.22) vs. 7.35 (3.95–12.77). SRTs measured with the LiveECAPMAPs were non-inferior to those measured with the ClinMAPs and not statistically different to the SRTs measured with the LiveBurstMAPs. ARTFit is a safe, quick, and reliable tool for audiologists to produce ECAP-based initial fitting maps in adults and young children who are not able to provide subjective feedback.

The optimal probe tone frequency for eSRT measurements at individual electrodes in children with cochlear implants

BACKGROUND

Higher probe tone frequencies have been shown to increase the elicitation rates in electrically evoked stapedius reflex threshold (eSRT) measurements.

OBJECTIVES

To determine the optimal probe tone frequency for contralateral eSRT measurements at individual electrodes in children with unilateral cochlear implants and to assess the relationship between eSRTs for this frequency and most comfortable levels (M-levels).

MATERIALS AND METHODS

Contralateral eSRT measurements with three probe tone frequencies (226, 678, and 1000 Hz) at individual electrodes were performed on 26 paediatric Advanced Bionics cochlear implant recipients.

RESULTS

The elicitation rates of eSRTs for 226, 678, and 1000 Hz probe tones were 73.08% (57/78), 88.46% (69/78), and 88.46% (69/78), respectively. The average eSRT for the 1000 Hz probe tone was significantly lower than those for 226 and 678 Hz probe tones (p<.001 and p=.009, respectively). ESRTs for the 1000 Hz probe tone and M-levels were significantly correlated at all tested electrodes (all p<.001).

CONCLUSIONS AND SIGNIFICANCE

The optimal probe tone frequency for contralateral eSRT measurement at individual electrodes in children with unilateral cochlear implants is 1000 Hz. ESRTs for the 1000 Hz probe tone are significantly correlated with M-levels and can be used to guide the M-levels setting in these children.

Wideband Acoustic Immittance in Cochlear Implant Recipients: Reflectance and Stapedial Reflexes

OBJECTIVES

to characterize differences in wideband power reflectance for ears with and without cochlear implants (CIs), to describe electrically evoked stapedial reflex (eSR)-induced changes in reflectance, and to evaluate the benefit of a broadband probe for reflex threshold determination for CI recipients. It was hypothesized that reflectance patterns in ears with CIs would be consistent with increased middle ear stiffness and that reflex thresholds measured with a broadband probe would be lower compared with thresholds obtained with a single-frequency probe.

DESIGN

Eleven CI recipients participated in both wideband reflectance and eSR testing. Ipsilateral reflexes were measured with three probes: a broadband chirp (swept from 200 to 8000 Hz), a 226 Hz tone, and a 678 Hz tone. Wideband reflectance measures acquired from 28 adults without CIs and with normal middle ear function served as a normative data set for comparison.

RESULTS

Considering the group data, average reflectance was significantly greater for ears with CIs across 250 to 891 Hz and 4238 to 4490 Hz compared with the normative data set, although individual reflectance curves were variable. Some CI recipients also had low 226 Hz admittance, which contributed to the group finding, considering the control group had clinically normal 226 Hz admittance by design. Electrically evoked stapedial reflexes were measurable in nine of 14 ears (64.3%) and in 24 of 46 electrodes (52.5%) tested. Reflex-induced changes in reflectance patterns were unique to the participant/ear, but similar across activators (electrodes) within a given ear. In addition, reflectance values at or above 1000 Hz were affected most by activating the stapedial reflex, even in ears with clinically normal 226 Hz admittance. This is a higher-frequency range than has been reported for acoustically evoked reflex-induced reflectance changes and is consistent with increased middle ear stiffness at rest. Electrically evoked reflexes could be measured more often with the 678 Hz or the broadband probe compared with the 226 Hz probe tone. Although reflex thresholds were lower with the broadband probe compared with the 678 Hz probe in 16 of 24 conditions, this was not a statistically significant finding (Wilcoxon signed-rank test; p = 0.072).

CONCLUSIONS

The applications of wideband acoustic immittance measurements (reflectance and reflexes) should also be considered for ears with CIs. Further work is needed to describe changes across time in ears with CIs to more fully understand the reflectance pattern indicating increased middle ear stiffness and to optimize measuring eSRs with a broadband probe.

Effect of Number of Electrodes Used to Elicit Electrical Stapedius Reflex Thresholds in Cochlear Implants

INTRODUCTION

When mapping cochlear implant (CI) patients with limited reporting abilities, the lowest electrical stimulus level that produces a stapedial reflex (i.e., the electrical stapedius reflex threshold [eSRT]) can be measured to estimate the upper bound of stimulation on individual or a subset of CI electrodes. However, eSRTs measured for individual electrodes or a subset of electrodes cannot be used to predict the global adjustment of electrical stimulation levels needed to achieve comfortable loudness sensations that can be readily used in a speech coding strategy. In the present study, eSRTs were measured for 1-, 4-, and 15-electrode stimulation to (1) determine changes in eSRT levels as a function of the electrode stimulation mode and (2) determine which stimulation mode eSRT levels best approximate comfortable loudness levels from patients' clinical maps.

METHODS

eSRTs were measured with the 3 different electrical stimulation configurations in 9 CI patients and compared with behaviorally measured, comfortable loudness levels or M-levels from patients' clinical maps.

RESULTS

A linear, mixed-effects, repeated-measures analysis revealed significant differences (p < 0.01) between eSRTs measured as a function of the stimulation mode. No significant differences (p = 0.059) were measured between 15-electrode eSRTs and M-levels from patients' clinical maps. The eSRTs measured for 1- and 4-electrode stimulation differed significantly (p < 0.05) from the M-levels on the corresponding electrodes from the patients' clinical map.

CONCLUSION

eSRT profiles based on 1- or 4-electrode stimulation can be used to determine comfortable loudness level on either individual or a subset of electrodes, and 15-electrode eSRT profiles can be used to determine the upper bound of electrical stimulation that can be used in a speech coding strategy.

The Long-Term Stability of the Electrical Stapedial Reflex Threshold

OBJECTIVES

To 1) describe changes in the electrical stapedial reflex threshold (eSRT), within and across patients over time and 2) to identify the clinical relationship between eSRT and an individual's upper limit of loudness.

STUDY DESIGN

Retrospective chart review and analysis using a multilevel modeling approach to describe changes in eSRT over time.

SETTING

Secondary care center.

PATIENTS

Two-hundred five cochlear implant recipients treated at the cochlear implant center during a 3-year time period.

INTERVENTION(S)

Cochlear implantation, eSRT testing, and, electrical upper limits of loudness.

MAIN OUTCOME MEASURE(S)

The eSRT over multiple appointments and the cochlear implant recipients' final upper limits of loudness.

RESULTS

Analysis of the eSRT testing indicated stability over time; no global trend was seen in trajectory across the population, b = -0.010, p = 0.899. The relationship between eSRT and user upper limits of loudness revealed a mean decrease of 19.47, units for manufacturer 1, 30.53 units for manufacturer 2, and 0.7 units for manufacturer 3.

CONCLUSION

Electrical stapedial reflex thresholds remain consistent for individual subjects over time with implant experience being the only variable correlated with eSRT stability (increase in 5% of one standard deviation with each year of experience). In addition, a clinical relationship between eSRT and behaviorally set upper limits of loudness was identified for all three cochlear implant manufacturers available in the United States.

Automated remote intraoperative cochlear implant device testing (CR220). Is it clinically efficient?

OBJECTIVES

To compare the clinical efficiency of the CR220 intraoperative remote assistant device used by the surgical team with that of the custom sound (CS) system used by an audiologist.

METHODS

This was a prospective clinical study in a quaternary care center (King Abdullah Ear Specialist Centre) in Riyadh, Saudi Arabia, between October 2018 and March 2019. We included adult and pediatric patients who underwent cochlear implant (CI) surgeries. For every participant, the intraoperative CI testing was performed via both the aforementioned methods. The time taken to complete the measurements with both approaches, including the time required by the audiologist to reach the operating room (OR) and to complete the test, was recorded.

RESULTS

There were no significant differences in the number of responding electrodes between the 2 approaches. For the 25 participants, the time taken for the measurements was 566 minutes with the CS and 173 with the CR220 systems. This significant difference indicates that considerable time can be saved.

CONCLUSION

The CR220 enables intraoperative CI electrode tests and auto-NRT measurements. Its ergonomics and ease-of-use help the surgical team conduct the tests without an audiologist in the OR, resulting in the efficient use of clinical resources. Further, the results generated were consistent with those of the CS system.

Multi-electrode sequential versus single electrode stimulation to elicit the stapedial reflex during cochlear implantation: Correlation with maximum comfort level

OBJECTIVES

To assess whether electrical stimulation sequentially delivered through 4 electrodes located in different cochlear areas may elicit the stapedial reflex at lower levels compared to single electrode stimulation and to correlate the sequentially obtained values with the maximum comfort level (C-level).

PATIENTS AND METHODS

A retrospective study was performed on 35 post-verbal adult patients (age 19-80 years) consecutively implanted in 2 cochlear implant centers, evaluating the level of stimulation (pulse width) necessary to electrically evoke the stapedial reflex with two different stimulation modalities: single electrode versus sequential 4 electrode stimulation. Threshold values were compared with C-level obtained at activation.

RESULTS

The average differences of pulse width and C-level were significantly smaller (P<0.0001) when the stapedial reflex was obtained with the sequential stimulation modality and reached statistical significance for every single electrode (P<0.0001).

CONCLUSIONS

Stapedial reflex thresholds obtained with sequential stimulation through 4 different electrodes significantly correlate to the C-level obtained at the first setting and may be helpful in defining the upper limit of the dynamic field during initial CI mapping.

Cochlear Implantation for Children and Adults with Severe-to-Profound Hearing Loss

Cochlear implants (CIs) have proven to be a useful treatment option for individuals with severe-to-profound hearing loss by providing improved access to one's surrounding auditory environment. CIs differ from traditional acoustic amplification by providing information to the auditory system via electrical stimulation. Both postlingually deafened adults and prelingually deafened children can benefit from a CI; however, outcomes with a CI can vary. Numerous factors can impact performance outcomes with a CI. It is important for the audiologist to understand what factors might play a role and impact performance outcomes with a CI so that they can effectively counsel the recipient and their family, as well as establish appropriate and realistic expectations with a CI. This review article will discuss the CI candidacy process, CI programming and postoperative follow-up care, as well as considerations across the lifespan that may affect performance outcomes with a CI.

Electrically-evoked auditory steady-state responses as neural correlates of loudness growth in cochlear implant users

Loudness growth functions characterize how the loudness percept changes with current level between the threshold and most comfortable loudness level in cochlear implant users. Even though loudness growth functions are highly listener-dependent, currently default settings are used in clinical devices. This study investigated whether electrically-evoked auditory steady-state response amplitude growth functions correspond to behaviorally measured loudness growth functions. Seven cochlear implant listeners participated in two behavioral loudness growth tasks and an EEG recording session. The 40-Hz sinusoidally amplitude-modulated pulse trains were presented to CI channels stimulating at a more apical and basal region of the cochlea, and were presented at different current levels encompassing the listeners' dynamic ranges. Behaviorally, loudness growth was measured using an Absolute Magnitude Estimation and a Graphic Rating Scale with loudness categories. A good correspondence was found between the response amplitude functions and the behavioral loudness growth functions. The results are encouraging for future advances in individual, more automatic, and objective fitting of cochlear implants.

Programming characteristics of cochlear implants in children: effects of aetiology and age at implantation

OBJECTIVE

We investigated effects of aetiology and age at implantation on changes in threshold (T) levels, comfortable (C) levels and dynamic range (DR) for cochlear implants (CIs) in children over the first five years of life.

DESIGN

Information was collected at 6 months post-activation of CIs, and at 3 and 5 years of age.

STUDY SAMPLE

One hundred and sixty-one children participating in the Longitudinal Outcomes of Children with Hearing Impairment (LOCHI) study.

RESULTS

Children with neural and structural cochlear lesions had higher T-levels and C-levels as compared to those without these conditions. Parameter settings varied from manufacturer's defaults more often in the former than in the latter group. Investigation of the effect of age at implantation for children without neural and structural cochlear lesions showed that those implanted at ≤12 months of age had higher T-levels and narrower DR at 6 months post-activation, as compared to the later-implanted group. For both early- and later-implanted groups, the C-levels at 6 months post-activation were lower than those at age 3 and 5 years. There were no significant differences in T-levels, C-levels, or DR between age 3 and 5 years.

CONCLUSIONS

Aetiology and age at implantation had significant effects on T-levels and C-levels.

Using Electrically-evoked Compound Action Potentials to Estimate Perceptive Levels in Experienced Adult Cochlear Implant Users

HYPOTHESIS

The cochlear implant (CI) fitting level prediction accuracy of electrically-evoked compound action potential (ECAP) should be enhanced by the addition of demographic data in models.

INTRODUCTION

No accurate automated fitting of CI based on ECAP has yet been proposed.

METHODS

We recorded ECAP in 45 adults who had been using MED-EL CIs for more than 11 months and collected the most comfortable loudness level (MCL) used for CI fitting (prog-MCL), perception thresholds (meas-THR), and MCL (meas-MCL) measured with the stimulation used for ECAP recording. Linear mixed models taking into account cochlear site factors were computed to explain prog-MCL, meas-MCL, and meas-THR.

RESULTS

Cochlear region and ECAP threshold were predictors of the three levels. In addition, significant predictors were the ECAP amplitude for the prog-MCL and the duration of deafness for the prog-MCL and the meas-THR. Estimations were more accurate for the meas-THR, then the meas-MCL, and finally the prog-MCL.

CONCLUSION

These results show that 1) ECAP thresholds are more closely related to perception threshold than to comfort level, 2) predictions are more accurate when the inter-subject and cochlear regions variations are considered, and 3) differences between the stimulations used for ECAP recording and for CI fitting make it difficult to accurately predict the prog-MCL from the ECAP recording. Predicted prog-MCL could be used as bases for fitting but should be used with care to avoid any uncomfortable or painful stimulation.

[Objective measures for setting the processors of cochlear implant systems : Use of discrimination functions and consideration of electrode profiles]

BACKGROUND

When setting the electrical stimulation level of cochlear implants during individual adjustment of the speech processor, especially in children, objective measures such as intracochlearly measured electrically evoked compound action potentials (eCAP) and intraoperative observation of electrically elicited stapedial reflexes (eSR) are indispensable. The benefit of these objective measures is based on the correlation between the derived response thresholds and psychometric data.

MATERIALS AND METHODS

The amplitude growth functions of eCAPs were measured intraoperatively for all electrodes in 30 ears of adult patients. The stimulus-dependent incidence of observable eSRs was recorded for all electrodes in 16 ears of adult patients. For evaluation of the data, new algorithms were applied which allowed the determination of thresholds without intervention of the investigator. Essential features were the conversion of observations into binary variables, and the consideration of logistic discrimination functions and their exceedance of a numeric threshold criterion.

RESULTS

Regarding the eCAP data, closer and significant correlations are observed between objective thresholds and psychometric measures in comparison to conventional procedures. Profiles are more efficient than pooled data. Significant correlations are also observed for eSR thresholds, albeit to a lesser extent and without an evident difference between profiles and pooled data.

CONCLUSION

Considering the by no means consistent international literature, the results illustrate the need for a consistent definition of response thresholds and the consideration of electrode profiles.