Intraoperative monitoring of hearing during cerebellopontine angle tumor surgery using transtympanic electrocochleography

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.

Acoustic component programming in children with cochlear implants using electrocochleography

OBJECTIVE

Objective measurements improve reliability and effectiveness of hearing assessment and cochlear implant (CI) programming in young children. In CI recipients with acoustic hearing in the implanted ear, electrocochleography (ECochG) can be conducted using intracochlear electrodes. The cochlear microphonic (CM) portion of ECochG has been shown to correlate with pure-tone audiometric thresholds in adult and paediatric CI recipients. Our goal was to determine if ECochG thresholds can be used to appropriately fit the acoustic component to the implanted ear in children.

DESIGN

Prospective.

STUDY SAMPLE

Eight children (aged 3.5-15.5 years, 10 ears) implanted with Advanced Bionics HiFocus Mid-Scala electrode array were recruited. CI ear acoustic thresholds were measured behaviourally and via ECochG. Two acoustic component enabled CI programs were created using the two sets of thresholds. Age and language appropriate speech outcomes and subjective feedback were obtained.

RESULTS

Speech scores were equivalent with the behavioural and ECochG thresholds programs. Subjectively, the ECochG thresholds program was preferred by 7/8 subjects. One subject preferred to use an electric only program.

CONCLUSION

Our data suggest that ECochG thresholds can be used to supplement the behavioural clinical methods and aid the reliable fitting of the acoustic component in paediatric CI recipients.

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.

Impact of Routine Plain X-ray on Postoperative Management in Cochlear Implantation

OBJECTIVES

To determine the benefit of a routine plain radiography (X-ray) for confirming the optimal electrode position in cochlear implant surgery.

MATERIALS AND METHODS

In total, 245 patients (135 males and 111 females) who underwent cochlear implantation in a single tertiary referral center were included in this study. Postoperative plain X-ray findings and electrophysiological tests were retrospectively analyzed.

RESULTS

The mean age was 11.4±14.6 years (range, 1-70 years). Overall, 196 (80%) patients were pediatric patients (age, <18 years) and 49 (20%) were adults (age, >18 years). The mean rotation of electrode arrays was 1.03±0.17 turns. The plain X-ray revealed that electrode misplacement was present in 5 patients (2%); incomplete insertion in 3 patients, and tip rollover and electrode migration in 1 patient each. A revision was performed for the last patient who had an extracochlear electrode position in the plain X-ray.

CONCLUSIONS

Postoperative imaging is mostly used to confirm the electrode array position after cochlear implant surgery. In addition, intraoperative evaluations have low positive predictive value and sensitivity. Thus, this study revealed that postoperative radiological imaging should be considered even when all intraoperative electrophysiological measures and surgical reports are normal.

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.

Self-Adjustment of Upper Electrical Stimulation Levels in CI Programming and the Effect on Auditory Functioning

OBJECTIVES

With current cochlear implants (CIs), CI recipients achieve good speech perception in quiet surroundings. However, in acoustically complex, real-life environments, speech comprehension remains difficult and sound quality often remains poor. It is, therefore, a challenge to program CIs for such environments in a clinic. The CI manufacturer Cochlear Ltd. recently introduced a remote control that enables CI recipients to alter the upper stimulation levels of their user programs themselves. In this concept, called remote assistant fitting (RAF), bass and treble controls can be adjusted by applying a tilt to emphasize either the low- or high-frequency C-levels, respectively. This concept of self-programming may be able to overcome limitations associated with fine-tuning the CI sound processor in a clinic. The aim of this study was to investigate to what extent CI recipients already accustomed to their clinically fitted program would adjust the settings in daily life if able to do so. Additionally, we studied the effects of these changes on auditory functioning in terms of speech intelligibility (in quiet and in noise), noise tolerance, and subjectively perceived speech perception and sound quality.

DESIGN

Twenty-two experienced adult CI recipients (implant use >12 months) participated in this prospective clinical study, which used a within-subject repeated measures design. All participants had phoneme scores of ≥70% at 65 dB SPL in quiet conditions, and all used a Cochlear Nucleus CP810 sound processor. Auditory performance was tested by a speech-in-quiet test, a speech-in-noise test, an acceptable noise level test, and a questionnaire about perceived auditory functioning, that is, a speech and sound quality (SSQ-C) questionnaire. The first session consisted of a baseline test in which the participants used their own CI program and were instructed on how to use RAF. After the first session, participants used RAF for 3 weeks at home. After these 3 weeks, the participants returned to the clinic for auditory functioning tests with their self-adjusted programs and completed the SSQ-C.

RESULTS

Fifteen participants (68%) adjusted their C-level frequency profile by more than 5 clinical levels for at least one electrode. Seven participants preferred a higher contribution of the high frequencies relative to the low frequencies, while five participants preferred more low-frequency stimulation. One-third of the participants adjusted the high and low frequencies equally, while some participants mainly used the overall volume to change their settings. Several parts of the SSQ-C questionnaire scores showed an improvement in perceived auditory functioning after the subjects used RAF. No significant change was found on the auditory functioning tests for speech-in-quiet, speech-in-noise, or acceptable noise level.

CONCLUSIONS

In conclusion, the majority of experienced CI users made modest changes in the settings of their programs in various ways and were able to do so with the RAF. After altering the programs, the participants experienced an improvement in speech perception in quiet environments and improved perceived sound quality without compromising auditory performance. Therefore, it can be concluded that self-adjustment of CI settings is a useful and clinically applicable tool that may help CI recipients to improve perceived sound quality in their daily lives.

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.

Non-invasive intraoperative monitoring of cochlear function by cochlear microphonics during cerebellopontine-angle surgery

In vestibular-schwannoma (VS) surgery, hearing-preservation rate remains low. Besides damage to the cochlear nerve, intraoperative cochlear ischemia is a potential cause of hearing loss. Here, we used non-invasive cochlear microphonic (CM) recordings to detect the cochlear vascular events of VS surgery. Continuous intraoperative CM monitoring, in response to 80-95 dB SPL, 1-kHz tone-bursts, was performed in two samples of patients undergoing retrosigmoid cerebellopontine-angle surgery: one for VS (n = 31) and one for vestibular neurectomy or vasculo-neural conflict causing intractable trigeminal neuralgia, harmless to hearing (n = 19, control group). Preoperative and postoperative hearings were compared as a function of intraoperative CM changes and their chronology. Monitoring was possible throughout except for a few tens of seconds when drilling or suction noises occurred. Four patterns of CM time course were identified, eventless, fluctuating, abrupt or progressive decrease. Only the VS group displayed the last two patterns, mainly during internal-auditory-canal drilling and the ensuing tumor dissection, always with postoperative loss of hearing as an end result. Conversely, eventless and fluctuating CM patterns could be associated with postoperative hearing loss when the cochlear nerve had been reportedly damaged, an event that CM is not meant to detect. Cochlear ischemia is a frequent event in VS surgery that leads to deafness. The findings that CM decrease raised no false alarm, and that CM fluctuations, insignificant in control cases, were easily spotted, suggest that CM intraoperative monitoring is a sensitive tool that could profitably guide VS surgery.

Intra-operative hearing monitoring methods in middle ear surgeries

Hearing loss is a condition affecting millions of people worldwide. Conductive hearing loss (CHL) is mainly caused by middle ear diseases. The low frequency area is the pivotal part of speech frequencies and most frequently impaired in patients with CHL. Among various treatments of CHL, middle ear surgery is efficient to improve hearing. However, variable success rates and possible needs for prolonged revision surgery still frustrate both surgeons and patients. Nowadays, increasing numbers of researchers explore various methods to monitor the efficacy of ossicular reconstruction intraoperatively, including electrocochleography (ECochG), auditory brainstem response (ABR), auditory steady state response (ASSR), distortion product otoacoustic emissions (DPOAE), subjective whisper test, and optical coherence tomography (OCT). Here, we illustrate several methods used clinically by reviewing the literature.

[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.

Surgery for sporadic vestibular schwannoma. Part III: Facial and auditory nerve function

OBJECTIVE

The aim of this analysis was to assess short-term and long-term outcomes with respect to the preservation of facial and auditory nerve function following surgery for sporadic vestibular schwannomas.

MATERIAL AND METHODS

The study included 220 consecutive patients operated on with the retrosigmoid (217) or translabyrinthine (3) approach. The mean extrameatal diameter of the tumor was 30mm. In 217 patients, gross total resection was performed and near-total in 3. Before surgery, the facial nerve (CNVII) weakness was found in 18% of patients and only 20% had serviceable hearing. Intraoperative neurophysiological CNVII monitoring was routinely used (the last 211 procedures). Intraoperative monitoring of the cochlear nerve function was used when the preservation of hearing was attempted (45 procedures).

RESULTS

The rate of CNVII continuity loss during surgery was 11%, however, this decreased to 6% in the second half of the series. Facial nerve function deteriorated, in 88% of the patients shortly after surgery. However, it improved in 87% in follow-up. Delayed CNVII palsy was found in 5% of the patients and had a good prognosis in 88%. Final satisfactory CNVII function (CNVII-SF, HB grades I-III) was achieved in 76% of the patients when excluding the anastomosis results, and 87% when including them. In recent years, the rate of CNVII-SF has risen to 94%. Non-serviceable hearing was preserved in 49% of the patients, on whom it was attempted.

CONCLUSION

Considering the size of the tumors and extent of the resections, the preservation of CNVII function is currently very high. A close surveillance of CNVII function evolution following surgery is mandatory, as 2/3 of the patients discharged with deep paresis will need different face reanimation procedures. The preservation of useful hearing is still problematic, especially in patients with large tumors.

Population-based prediction of fitting levels for individual cochlear implant recipients

OBJECTIVES

This study analyzed the predictability of fitting levels for cochlear implant recipients based on a review of the clinical levels of the recipients.

DESIGN

Data containing threshold levels (T-levels) and maximum comfort levels (M-levels) for 151 adult subjects using a CII/HiRes 90K cochlear implant with a HiFocus 1/1 J electrode were used. The 10th, 25th, 50th, 75th and 90th percentiles of the T- and M-levels are reported. Speech perception of the subjects, using a HiRes speech coding strategy, was measured during routine clinical follow-up.

RESULTS

T-levels for most subjects were between 20 and 35% of their M-levels and were rarely (<1/50) below 10% of the M-levels. Furthermore, both T- and M-levels showed an increase over the first year of follow-up. Interestingly, levels expressed in linear charge units showed a clear increase in dynamic range (DR) over 1 year (29.8 CU; SD 73.0), whereas the DR expressed in decibels remained stable. T-level and DR were the only fitting parameters for which a significant correlation with speech perception (r = 0.34, p < 0.01, and r = 0.33, p < 0.01, respectively) could be demonstrated. Additionally, analysis showed that T- and M-level profiles expressed in decibels were independent of the subjects' across-site mean levels. Using mixed linear models, predictive models were obtained for the T- and M-levels of all separate electrode contacts.

CONCLUSIONS

On the basis of the data set from 151 subjects, clinically applicable predictive models for T- and M-levels have been obtained. Based on one psychophysical measurement and a population-based T- or M-level profile, individual recipients' T- and M-levels can be approximated with a closed-set formula. Additionally, the analyzed fitting level data can serve as a reference for future patients.

The importance of electrically evoked stapedial reflex in cochlear implant

Introdução

A determinação da área dinâmica do implante coclear é um dos procedimentos mais importantes em sua programação. O uso de medidas objetivas, em especial a do limiar do reflexo estapédico evocado eletricamente, pode contribuir para a definição deste campo, principalmente em crianças ou em indivíduos com múltiplos comprometimentos, pois fornecem valores específicos que servem como base no início da programação do implante coclear.

Objetivo

Verificar por meio de uma revisão a utilização do limiar do reflexo estapédico evocado ele- tricamente durante o processo de ativação e de mapeamento do implante coclear. Métodos: Levantamento bibliográfico nas plataformas Pubmed e Bireme e nas bases de dados MedLine, LILACS e SciELO, com buscas padronizadas até setembro de 2012, utilizando-se palavras-chave. Para a seleção e avaliação dos estudos científicos levantados, foram estabelecidos critérios, contemplando os seguintes aspectos: autor, ano/local, grau de recomendação/nível de evidência científica, objetivo, amostra, faixa etária, média de idade em anos, testes avaliativos, resultados e conclusão.

Resultados

Dos 7.304 artigos encontrados, 7.080 foram excluídos pelo título, 152 pelo resumo, 17 pela leitura do artigo, 43 eram repetidos e 12 foram selecionados para o estudo. Conclusão: O reflexo estapédico evocado eletricamente é capaz de auxiliar na programação do implante coclear, principalmente em pacientes que apresentam respostas inconsistentes.

© 2014 Associação Brasileira de Otorrinolaringologia e Cirurgia Cérvico-Facial. Publicado por Elsevier Editora Ltda. Todos os direitos reservados.

A clinical study of electrophysiological correlates of behavioural comfort levels in cochlear implantees

OBJECTIVES

Indications for cochlear implantation have expanded today to include very young children and those with syndromes/multiple handicaps. Programming the implant based on behavioural responses may be tedious for audiologists in such cases, wherein matching an effective Measurable Auditory Percept (MAP) and appropriate MAP becomes the key issue in the habilitation program. In 'Difficult to MAP' scenarios, objective measures become paramount to predict optimal current levels to be set in the MAP. We aimed to (a) study the trends in multi-modal electrophysiological tests and behavioural responses sequentially over the first year of implant use; (b) generate normative data from the above; (c) correlate the multi-modal electrophysiological thresholds levels with behavioural comfort levels; and (d) create predictive formulae for deriving optimal comfort levels (if unknown), using linear and multiple regression analysis.

METHODS

This prospective study included 10 profoundly hearing impaired children aged between 2 and 7 years with normal inner ear anatomy and no additional handicaps. They received the Advanced Bionics HiRes 90 K Implant with Harmony Speech processor and used HiRes-P with Fidelity 120 strategy. They underwent, impedance telemetry, neural response imaging, electrically evoked stapedial response telemetry (ESRT), and electrically evoked auditory brainstem response (EABR) tests at 1, 4, 8, and 12 months of implant use, in conjunction with behavioural mapping. Trends in electrophysiological and behavioural responses were analyzed using paired t-test. By Karl Pearson's correlation method, electrode-wise correlations were derived for neural response imaging (NRI) thresholds versus most comfortable level (M-levels) and offset based (apical, mid-array, and basal array) correlations for EABR and ESRT thresholds versus M-levels were calculated over time. These were used to derive predictive formulae by linear and multiple regression analysis. Such statistically predicted M-levels were compared with the behaviourally recorded M-levels among the cohort, using Cronbach's alpha reliability test method for confirming the efficacy of this method.

RESULTS

NRI, ESRT, and EABR thresholds showed statistically significant positive correlations with behavioural M-levels, which improved with implant use over time. These correlations were used to derive predicted M-levels using regression analysis. On an average, predicted M-levels were found to be statistically reliable and they were a fair match to the actual behavioural M-levels. When applied in clinical practice, the predicted values were found to be useful for programming members of the study group. However, individuals showed considerable deviations in behavioural M-levels, above and below the electrophysiologically predicted values, due to various factors. While the current method appears helpful as a reference to predict initial maps in 'difficult to Map' subjects, it is recommended that behavioural measures are mandatory to further optimize the maps for these individuals.

CONCLUSION

The study explores the trends, correlations and individual variabilities that occur between electrophysiological tests and behavioural responses, recorded over time among a cohort of cochlear implantees. The statistical method shown may be used as a guideline to predict optimal behavioural levels in difficult situations among future implantees, bearing in mind that optimal M-levels for individuals can vary from predicted values. In 'Difficult to MAP' scenarios, following a protocol of sequential behavioural programming, in conjunction with electrophysiological correlates will provide the best outcomes.

Electrophysiological Correlates of Behavioral Comfort Levels in Cochlear Implantees: A Prospective Study

Indications for cochlear implantation have expanded today to include very young children and those with syndromes/multiple handicaps. Programming the implant based on behavioral responses may be tedious for audiologists in such cases, wherein matching an effective MAP and appropriate MAP becomes the key issue in the habilitation program. In 'Difficult to MAP' scenarios, objective measures become paramount to predict optimal current levels to be set in the MAP. We aimed, (a) to study the trends in multi-modal electrophysiological tests and behavioral responses sequentially over the first year of implant use, (b) to generate normative data from the above, (c) to correlate the multi-modal electrophysiological thresholds levels with behavioral comfort levels, and (d) to create predictive formulae for deriving optimal comfort levels (if unknown), using linear and multiple regression analysis. This prospective study included ten profoundly hearing impaired children aged between 2 and 7 years with normal inner ear anatomy and no additional handicaps. They received the Advanced Bionics HiRes 90K Implant with Harmony Speech processor and used HiRes-P with Fidelity 120 strategy. They underwent, Impedance Telemetry, Neural Response Imaging, Electrically Evoked Stapedial Response Telemetry and Electrically Evoked Auditory Brainstem Response tests at 1, 4, 8 and 12 months of implant use, in conjunction with behavioral Mapping. Trends in electrophysiological and behavioral responses were analyzed using paired t test. By Karl Pearson's correlation method, electrode-wise correlations were derived for NRI thresholds versus Most Comfortable Levels (M-Levels) and offset based (apical, mid-array and basal array) correlations for EABR and ESRT thresholds versus M-Levels were calculated over time. These were used to derive predictive formulae by linear and multiple regression analysis. Such statistically predicted M-Levels were compared with the behaviorally recorded M-Levels among the cohort, using Cronbach's Alpha Reliability test method for confirming the efficacy of this method. NRI, ESRT and EABR thresholds showed statistically significant positive correlations with behavioral M-Levels, which improved with implant use over time. These correlations were used to derive predicted M-Levels using regression analysis. Such predicted M-Levels were found to be in proximity to the actual behavioral M-Levels recorded among this cohort and proved to be statistically reliable. When clinically applied, this method was found to be successful among subjects of our study group. Although there existed disparities of a few clinical units, between the actual and predicted comfort levels among the subjects, this statistical method was able to provide a working MAP, close to the behavioral MAP used by these children. The results help to infer that behavioral measurements are mandatory to program cochlear implantees, but in cases where they are difficult to obtain, this study method may be used as reference for obtaining additional inputs, in order to set an optimal MAP. The study explores the trends and correlations between electrophysiological tests and behavioral responses, recorded over time among a cohort of cochlear implantees and provides a statistical method which may be used as a guideline to predict optimal behavioral levels in difficult situations among future implantees. In 'Difficult to MAP' scenarios, following a protocol of sequential behavioral programming, in conjunction with electrophysiological correlates will provide the best outcomes.

Feasibility of an objective electrophysiological loudness scaling: a kernel-based novelty detection approach

OBJECTIVE

The objective of our research is to structure a foundation for an electrophysiological loudness scaling measurement, in particular to estimate an uncomfortable loudness (UCL) level by using the hybrid wavelet-kernel novelty detection (HWND).

METHODS AND MATERIALS

Late auditory evoked potentials (LAEPs) were obtained from 20 normal hearing adults. These LAEPs were stimulated by 4 intensity levels (60 decibel (dB) sound pressure level (SPL), 70 dB SPL, 80 dB SPL, and 90 dB SPL). We have extracted the habituation correlates in LAEPs by using HWND. For this, we employed a lattice structure-based wavelet frame decompositions for feature extraction combined with a kernel-based novelty detector.

RESULTS

The group results showed that the habituation correlates degrees, i.e., relative changes within the sweep sequences, were significantly different among 60 dB SPL, 70 dB SPL, 80 dB SPL, and 90 dB SPL stimulation level, independently from the intensity related amplitude information in the averaged LAEPs. At these particular intensities, 60% of the subjects show the correlation between the novelty measures and the stimulation levels resembles a loudness scaling function, in reverse. In this paper, we have found a correlation in between the novelty measures and loudness perception as well. We have found that high ranges of loudness levels such as loud, upper level and too loud show generally 4.88% of novelty measures and comfortable ranges of loudness levels, i.e., soft, comfortable but soft, comfortable loud and comfortable but loud are generally have 12.29% of novelty measures. Additionally, we demonstrated that our sweep-to-sweep basis of post processing scheme is reliable for habituation extraction and offers an advantage of reducing experimental time as the proposed scheme need less than 20% of single sweeps in comparison to the amount that are commonly used in arithmetical average for a meaningful result.

CONCLUSIONS

We assessed the feasibility of habituation correlates for an objective loudness scaling. With respect to this first feasibility study, the presented results are promising when using the described signal processing and machine learning methodology. For the group results, the novelty measures approach is able to discriminate 60 dB, 70 dB, 80 dB and 90 dB stimulated sweeps. In addition, a correlation between the novelty measures and the subjective loudness scaling is observed. However, more loudness perception and frequency specific experiments need to be conducted to determine the UCL novelty measures threshold as well as clinically oriented studies are necessary to evaluate whether this approach might be used in the objective hearing instrument fitting procedures.

Intra- and postoperative electrically evoked stapedius reflex thresholds in children with cochlear implants

OBJECTIVES

The aim of this study was to investigate whether there is a significant correlation between intra- and postoperative electrically evoked stapedius reflex thresholds (eSRTs) in children with cochlear implants.

METHODS

Sixty-five pediatric cochlear implant users were included in this study. All patients had congenital prelingual hearing loss. The round window approach was used in all patients. The eSRTs were intraoperatively measured using the 1st, 3rd, 6th and 12th electrodes of the cochlear implant. The measurements taken during the first fitting of the device were taken again one month after surgery. We used paired-sample t-tests to determine the correlation between intra- and postoperative eSRTs.

RESULTS

The eSRT analysis revealed a statistically significant difference between the intra- and postoperative thresholds. A correlation analysis did not reveal any correlation between intra- and postoperative eSRTs.

CONCLUSION

Intraoperative eSRT measurements were unable to predict early postoperative eSRTs.

Cochlear implantation: current and future device options

Today most cochlear implant users achieve above 80% on standard speech recognition in quiet testing, and enjoy excellent device reliability. Despite such success, conventional designs often fail to provide the frequency resolution required for complex listening tasks. Furthermore, performance variability remains a vexing problem, with a select group of patients performing poorly despite using the most recent technologies and processing strategies. This article provides a brief history of the development of cochlear implant technologies, reviews current implant systems from all 3 major manufacturers, examines recently devised strategies aimed at improving device performance, and discusses potential future developments.

How reliable is visual assessment of the electrically elicited stapedius reflex threshold during cochlear implant surgery, compared with tympanometry?

OBJECTIVES

To assess the reliability of visually assessed thresholds of the electrically elicited stapedius reflex, recorded during cochlear implant surgery, compared with intra-operative tympanometric threshold assessment. Intra-operatively recorded electrically elicited stapedius reflex thresholds vary considerably, and differ from those measured post-operatively by means of impedance changes (i.e. using tympanometry). Thus, any confounding effect of different intra-operative techniques and visual assessment inaccuracies should be excluded.

METHODS

Both techniques (i.e. visual observation and tympanometry) were performed intra-operatively in six patients, and threshold values were compared.

RESULTS

Recorded electrically elicited stapedius reflex thresholds were very similar for both techniques. Visually assessed thresholds were slightly higher in some cases and lower in others, compared with tympanometric thresholds.

DISCUSSION

There was almost no difference between reflex thresholds measured with the two different techniques under the same intra-operative conditions. Therefore, we conclude that differences between intra- and post-operative thresholds are not due to the use of different measuring techniques. The main reason for such differences is probably the influence of intra-operative narcotics on reflex thresholds.

Cochlear implantation surgery without posterior tympanotomy: can we still improve it?

CONCLUSION

The amendments made to pre-existing transcanal approaches limit the possibility of extrusion of the electrode and reduce the time of 'blind' surgery.

OBJECTIVE

Alternative techniques to classic mastoidectomy and posterior tympanotomy for cochlear implantation have already been described but their main drawbacks result in either: (i) the risk of an electrode extrusion through the skin as the groove is drilled into the auditory canal or (ii) the risk of a facial nerve injury as the tunnel is drilled blindly into the posterior canal wall. The aim of this study was to describe and evaluate a new transcanal approach for cochlear implantation ruling out these difficulties.

PATIENTS AND METHODS

Through a minimal retroauricular skin incision, a cochleostomy is performed directly via the auditory canal. The passage for the electrode is performed after drilling both a suprameatal hollow and a 1.5 mm hole into the superior-posterior canal wall, which opens the facial recess by an anterior approach. Thanks to this hole a transwall tunnel can afterwards be dug safely.

RESULTS

Twenty-three patients (8 adults, 15 children) were implanted without any difficulty. The mean follow-up was 22 months. No postoperative complication was observed.

Auditory brainstem circuits that mediate the middle ear muscle reflex

The middle ear muscle (MEM) reflex is one of two major descending systems to the auditory periphery. There are two middle ear muscles (MEMs): the stapedius and the tensor tympani. In man, the stapedius contracts in response to intense low frequency acoustic stimuli, exerting forces perpendicular to the stapes superstructure, increasing middle ear impedance and attenuating the intensity of sound energy reaching the inner ear (cochlea). The tensor tympani is believed to contract in response to self-generated noise (chewing, swallowing) and non-auditory stimuli. The MEM reflex pathways begin with sound presented to the ear. Transduction of sound occurs in the cochlea, resulting in an action potential that is transmitted along the auditory nerve to the cochlear nucleus in the brainstem (the first relay station for all ascending sound information originating in the ear). Unknown interneurons in the ventral cochlear nucleus project either directly or indirectly to MEM motoneurons located elsewhere in the brainstem. Motoneurons provide efferent innervation to the MEMs. Although the ascending and descending limbs of these reflex pathways have been well characterized, the identity of the reflex interneurons is not known, as are the source of modulatory inputs to these pathways. The aim of this article is to (a) provide an overview of MEM reflex anatomy and physiology, (b) present new data on MEM reflex anatomy and physiology from our laboratory and others, and (c) describe the clinical implications of our research.

Anatomic logic of the foramen Luschka in neurootologic surgery

The authors emphasise the key role of the state of the foramen Luschka in indication of neurootologic surgical approaches. Blockage of the foramen of Luschka with a medium or big tumour may impaire the CSF circulation. In such case the lateral transtemporal approaches--translabyrinthine and transotic are the best options. In all other situations where there is no blockage of the CSF circulation in the affected pontocerebellar angle the choice of a surgical approach is determined by the state of hearing and character of disease. Surgical indications schould be elective and individually considered.

Preventing hearing damage using topical dexamethasone during reversible cochlear ischemia: an animal model

HYPOTHESIS

Local application of dexamethasone to the round window (RW) niche prevents cochlear damage caused by local reversible ischemia.

BACKGROUND

Cochlear ischemia induced by internal auditory artery (IAA) compression/stretching is thought to cause postoperative sensory hearing loss after attempted hearing preservation removal of acoustic neuroma tumors. Dexamethasone administered to the RW niche traveling through the membrane to the cochlear fluids may prevent ischemic damage.

MATERIALS AND METHODS

Ten young albino rabbits were used for this study. Ischemic episodes were induced by compressing the IAA. Laser Doppler cochlear blood flow was measured using a probe positioned at the RW niche. Transtympanic electrocochleography was measured at 4, 8, and 12 kHz. In 5 test ears, dexamethasone was administered topically at the RW for approximately 50 minutes before the IAA compressions, whereas in 5 control ears, saline was applied in the same way. Each ear underwent one 10-minute IAA compression with a 60-minute postischemic period of transtympanic electrocochleography monitoring.

RESULTS

In both control- and dexamethasone-treated ears, ischemic episodes measured by Laser Doppler cochlear blood flow were comparable. Fifty minutes after IAA decompression, in dexamethasone-pretreated ears, cochlear microphonic and compound action potential amplitudes at all test frequencies were 10 to 15% less reduced than those in control ears. Compound action potential latencies in dexamethasone-pretreated ears resulted in shorter latency delay than in control ears.

CONCLUSION

The RW seems to be an efficacious route for the administration of dexamethasone into the inner ear. Dexamethasone showed a protective effect on cochlear function after local ischemia. Transtympanic electrocochleography was found to be a sufficient and effective tool in monitoring hearing.

[Cochlear implants in isolated temporal bones: evaluation of electrode position with 64-slice computed tomography]

BACKGROUND

For the functional outcome after cochlear implant surgery, the electrode position is of essential importance. Therefore, radiological techniques to localize the electrode within the cochlea are becoming increasingly important. In our study, we used multi-slice computed tomography (CT) to find radiological criteria to allocate the electrode within the cochlea.

METHODS

Ten Nucleus 24 RCA electrodes were implanted into isolated human temporal bones using an extended cochleostomy and the Advance Off-Stylet technique. Five electrodes were implanted into the scala tympani and five into the scala vestibuli. After implantation, the temporal bones were blinded to the radiologist, and 64-slice CT scans were performed and analysed.

RESULTS AND CONCLUSIONS

In all 10 cases, the surgical positioning of the electrode was equal to the radiological analysis of the CT scans. Radiological criteria were found that permit correct identification of the electrode within the cochlea. We think that this technique is sufficient for most questions concerning quality control and is widely available.

Comparing the habituation of late auditory evoked potentials to loud and soft sound

The objective fitting of hearing aids and cochlear implants remains a challenge. In particular, the determination of whether sound is perceived as too loud or comfortable represents an unsolved problem in noncooperative patients. In a first step of an ongoing study, we assess the feasibility of habituation correlates in late auditory evoked potentials (LAEPs) to discriminate between a soft sound (SS) of 50 dB SPL and a loud sound (LS) of 100 dB SPL. We applied a new sweep-to-sweep time-scale coherence measure to analyse the habituation in LAEPs, i.e., relative changes within sweep sequences. From the comparison between both stimulation levels, a total discrimination of responses to SS and LS in the individual normal hearing subject was possible. As just relative changes in SS and LS sweep sequences were considered, purely exogenously driven morphological alternations in the responses such as intensity related amplitude and latency changes were excluded from the analysis. It is concluded that the proposed method allows for the reliable detection of auditory habituation and differentiation of SS from LS. The proposed scheme might provide an electrophysiological measurement and signal processing framework for the objective detection of the most comfortable loudness level and can be used in further, more clinically oriented studies.