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 Table of Contents  
REVIEW ARTICLE
Year : 2016  |  Volume : 3  |  Issue : 1  |  Page : 1-8

Evaluation of factors that influence cochlear implant performance


1 Audiology Unit, Department of Otorhinolaryngology, Suez Canal University, Egypt
2 Department of Otorhinolaryngology, Faculty of Medicine, Alexandria University, Alexandria, Egypt

Date of Submission18-Jan-2016
Date of Acceptance28-Apr-2016
Date of Web Publication28-Sep-2016

Correspondence Address:
Vergena S Ahmed Elkayal
75 Masr Street, Ismailia
Egypt
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/2314-8667.191235

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  Abstract 

Background
One of the primary goals of cochlear implantation is open-set auditory-only speech understanding in everyday listening environments. An understanding of the etiology and neurocognitive factors that contribute to a favorable outcome after cochlear implantation would potentially allow clinicians to predict the results for a cochlear implant patient. The ability to discriminate small acoustic differences is very important for the perception and processing of speech signals. The mismatch negativity (MMN) method is an objective tool that provides a measure of automatic stimuli discrimination.
Objective of the study
The aim of this study was to classify the communicative performance of children with cochlear implants and verify this outcome by means of electrophysiological biomarkers.
Methods
The study was carried out in three phases: phase I included completing an audiological data information sheet for all patients, with data taken from their records, which included demographic data, preoperative and postoperative audiological evaluation, operative detailed information, cochlear implant mapping data, and preoperative auditory verbal therapy details as regards regularity and benefit. Phase II involved classifying the patients’ communicative performance according to a phoniatric evaluation protocol into poor, fair, and good response, determining behavioral pure tone aided thresholds with their cochlear implants, and conducting electrophysiological studies ‘P1 and MMN’ for those with aided thresholds in the long-term average speech spectrum with their cochlear implant. Phase III entailed verification of factors that affect the outcome of all cochlear implant users.
Results
Age of cochlear implantation, cause of hearing loss, comorbidity, preoperative electrophysiological test results, and radiological findings are variables affecting cochlear implant performance and affecting the patient's communicative performance, whereas sex of the patient and number of stimulated electrodes are variables not affecting the cochlear implant performance.
Conclusion
Early cochlear implantation and good auditory verbal therapy have better outcomes as regards listening and communication skills. Cortical auditory evoked potential (P1) and MMN might provide a clinical tool to monitor aural rehabilitation outcome. These objective electrophysiological parameters may also be used as prognostic indicators for speech and language outcome.

Keywords: benefit of auditory verbal therapy, benefit of cochlear implant, cochlear implant, evaluation, mismatch negativity


How to cite this article:
Ahmed Elkayal VS, Mourad MI, Elbanna MM, Mohamed Talaat MA. Evaluation of factors that influence cochlear implant performance. Adv Arab Acad Audio-Vestibul J 2016;3:1-8

How to cite this URL:
Ahmed Elkayal VS, Mourad MI, Elbanna MM, Mohamed Talaat MA. Evaluation of factors that influence cochlear implant performance. Adv Arab Acad Audio-Vestibul J [serial online] 2016 [cited 2018 Aug 14];3:1-8. Available from: http://www.aaj.eg.net/text.asp?2016/3/1/1/191235


  Introduction Top


Cochlear implants are among the great success stories of modern medicine. The principal cause of hearing loss is damage to or complete destruction of the sensory hair cells. Direct stimulation of the auditory nerve is produced by currents delivered through electrodes placed in the scala tympani. The array is inserted through a drilled opening made by the surgeon in the bony shell of the cochlea overlying the scala tympani and close to the base of the cochlea (called a ‘cochleostomy’) [1].

Cochlear implant is an electronic device that restores hearing to severely and profoundly hearing-impaired adults and children. Its components can be bifurcated into internal and external parts. The internal components – the receiver-stimulator and the electrode – are surgically placed behind the ear, and the electrode is placed within the cochlea. The external components are worn much like a hearing aid, and consists of a microphone, a processor, and a transmitter [2].

Acoustic signals are received, processed, and transmitted to the internal component (receiver-stimulator) transcutaneously and are then delivered as electrical signals through the electrode array directly (bypassing the hair cells) to the auditory nerve dendrites and the spiral ganglion cells. Finally these stimulations are interpreted as ‘meaningful’ sound by the auditory central nervous system and the brain [3].

Cochlear implants have also been shown to result in successful speech perception in children. Currently, the earliest age of implantation is 12 months, but there are reasons to reassess this age threshold. A younger age of implantation may limit the negative consequences of auditory deprivation and may allow more efficient acquisition of speech and language [4].

Before implantation, a trial period with appropriate amplification combined with intensive auditory training should be attempted to ensure that maximal benefit is achieved [5].

Several factors have been reported to have an impact on the ability of prelingually deaf children to develop oral language skills after cochlear implantation. The most important and consistently reported variable that influences the ability to use auditory-only communication is the age at which the child is implanted [6]. Communication mode after implantation has also been frequently reported to be a factor that contributes to final speech and language outcome, with oral-only communication producing speech and language results superior to those observed in children who use a combination of sign and spoken language (total communication) [7],[8].

The wide range of speech perception abilities exhibited by cochlear implant recipients may depend in part upon differences in the central auditory processing abilities of implant users. One way to assess central auditory function in these individuals is to measure speech-evoked cortical potentials. In particular, measuring cortical potentials that reflect auditory discrimination may provide insight into the central mechanisms underlying speech perception [9].

Moreover, if those cortical potentials can be recorded from cochlear implant users, comparing the potentials to the responses measured in normal listeners should indicate whether the brain's response to speech mediated by a cochlear implant is similar to the brain's response to speech processed by a normal cochlea. From a theoretical standpoint, the presence of cortical potentials in cochlear implant users may provide a unique window to viewing the central auditory system [9].

Mismatch negativity (MMN) is an event-related auditory potential that reflects the neurophysiologic processing of stimulus differences [10]. Because it originates in higher auditory and nonauditory centers [11],[12],[13], it provides a way to investigate the central auditory processes underlying discrimination.

Much of the research, since children began to receive cochlear implants, has been directed toward documenting the degree and scope of speech and language benefit provided by cochlear implants and evaluating factors that account for individual differences in outcomes of children receiving these devices.

Small but statistically significant gains in speech intelligibility over preimplant performance using cochlear implants were also found in earlier studies [14].


  Objectives Top


The aim of the study was to evaluate the relationship between performance in terms of electrophysiological test results and the patient's communication skills development.

Experimental design

This is a retrospective review of cochlear implant performance at the Audiology Unit, ENT Department, Alexandria University Hospital, in the period from 2000 to 2012.


  Materials and methods Top


Materials

All patients gave their formal consent. The protocol was approved the Ethical Committee of the Faculty Faculty of Medicine, Alexandria University, Alexandria, Egypt. The study was carried out on all patients who have received cochlear implants independent of age, sex, and etiology of hearing loss. All patients received cochlear implants at the Audiology Unit, ENT Department, Alexandria University Hospital, in the period from 2000 to 2012.

An audiological data collection sheet was filled for all patients, with data taken from their records.

Only 25 patients attended visits for electrophysiological tests. Pure tone aided thresholds with cochlear implants were referred for phoniatric evaluation.

The study was carried out in three phases: phase I involved completing an audiological data collection sheet for all patients regarding their audiological data, with information taken from their records; phase II involved classification of patients’ performance according to phoniatric evaluation into poor, fair, and poor response. Determination of behavioral pure tone aided thresholds with patients’ cochlear implants and electrophysiological studies ‘P1 and MMN’ were carried out for those with satisfactory aided thresholds with their cochlear implant. Phase III involved verification of factors that affect outcome of all cochlear implant users.

Phoniatric evaluation

The phoniatric evaluation was performed preoperatively and postoperatively for determination of the studied children's communicative ability and grade of improvement.

Preoperative data were collected from the patients’ records in the Phoniatric Unit, Alexandria University, and the postoperative data reflect their current communication status.

In the Phoniatric Unit all studied children were subjected to the following:

  1. Psychometric aptitude assessment.
  2. A Quasi-objective description of communicative ability using a questionnaire and through scaling and grading of progress from lower stages to higher stages in communicative performance. The assessment was done by the phoniatrician, who also recorded the necessary responses from parents for the determination of:
  3. The mode of communication used by the child.
  4. Approximate language age.
  5. Speech intelligibility with reference to everyday situational responses and use of lip-reading ability.
  6. Grade of auditory performance.
  7. Levels of receptive language skills and expressive language skills.
  8. The auditory ability of children for various vowels and consonants, reflecting their ability to identify and discriminate various speech sounds using the Ling test.
  9. Response to auditory verbal therapy and grading of benefit into poor, fair, and good response.
  10. For determination of the degree of benefit, the previous information collected preoperatively and postoperatively for each patient was compared. The selection of the criteria for indicating the degree of benefit was guided by the phoniatrician's observations, the therapist's feedback, and the parents’ response.


Good response was documented if the child showed positive response in at least five of the following criteria:

  1. Completion of therapeutic level and/or transition to a higher level.
  2. Increase in vocabulary by more than 50 words.
  3. Increase in language age by more than 6–12 months.
  4. Consistent use of verbal mode of communication.
  5. Lip-reading ability extended to words that differ in consonants.
  6. Connected speech intelligible to strangers within context and with lip-reading cues.
  7. Increase in auditory performance by more than two stages.
  8. Increase in receptive language skill by more than two levels.
  9. Demonstrated increase in expressive language level by more than two levels.
  10. Able to repeat the following (/m/,/a/,/i/,/u/,/ʃ/,/f/,/s/) speech sounds consistently when sound is presented auditorily with no visual cueing, isolated or, in case of adequate comprehension ability, in the form of monosyllabic (/mo:z/,/bat/,/feel/,/fool/,/ʃæms/,/fol/,/se:f/) word contexts at 20 cm distance at 60 dB and variable periods in a quiet room.


Fair response was documented if the child showed positive response in at least five of the following criteria:

  1. Demonstrated steady progress in one level of the therapeutic intervention program.
  2. Increase in vocabulary by at least 50 words.
  3. Demonstrated improvement in language age by 6–12 months.
  4. Showed improvement in prelinguistic skills.
  5. Lip-reading ability improved to common words or phrases.
  6. Connected speech intelligible to family members within context and with lip-reading cues.
  7. Increase in auditory performance for at least two stages.
  8. Increase in receptive language skill by one level for at least two stages.
  9. Demonstrated increase in expressive language level for one level for at least two stages.
  10. Inconsistently able to repeat the following (/m/,/a/,/i/,/u/,/ʃ/,/f/,/s/) speech sounds when presented auditorily with no visual cueing, isolated or in monosyllabic word contexts (/mo:z/,/bat/,/feel/,/fool/,/ʃæms/,/fol/,/se:f/), at 20 cm distance at 60 dB and variable periods in a quiet room and showing a consistent pattern in the recognition of sound in a specific auditory range not previously recognized.


Poor response was documented if the child showed positive response in at least five of the following criteria:.

  1. Poor progress in one level of the therapeutic intervention program.
  2. Increase in vocabulary size by not more than 50 words.
  3. No change in language age.
  4. Nonverbal mode of communication.
  5. Improvement in lip-reading ability.
  6. Significant improvement in intelligibility of speech.
  7. Increase in auditory performance by not more than one stage.
  8. Change in the receptive language skill level by not more than one stage.
  9. Change in the expressive language skill level by not more than one stage.
  10. Unable to repeat the following (/m/,/a/,/i/,/u/,/ʃ/,/f/,/s/) speech sounds consistently when the sounds are presented auditorily only. With the help of visual cueing, recognition of a few speech sounds, isolated or in monosyllabic word (/mo:z/,/bat/,/feel/,/fool/,/ʃæms/,/fol/,/se:f/) contexts, at 20 cm distance at 60 dB and variable periods in a quiet room is possible.


Auditory electrophysiological test

Obligatory cortical auditory evoked potential (P1–N1–P2) and auditory MMN are objective tests that reflect cortical maturation and cortical sound discrimination abilities.

Stimulus parameters

Consonant vowel natural speech syllable KA was used in oddball paradigm with KA of 150 ms duration as a standard and KAA of 300 ms duration as a deviant stimulus. These stimuli were recorded using Cool Edit 2000 (Adobe systems; Adobe Audition, United states) computer-based program.

The stimuli were presented via a loudspeaker with an intensity of 50 dBSL based on their aided behavioral thresholds using Intelligent Hearing Systems for stimulating, recording, and analysis of the response.

The recording window was 400 ms.

The standard deviant probability was 8: 2.

Recording parameters

Single channel recording was adopted with an inverting ‘reference’ electrode on the mastoid contralateral to the implant, the active ‘noninverting’ at Cz, and the ground electrode at the forehead (Fz). Low pass filter was 30 Hz, high pass filter was 1 Hz, and gain was 100.

Statistical analysis of the data [15]

Data were fed into the computer and analyzed using IBM SPSS software package, version 20.0. Qualitative data were described using number and percentage. Quantitative data were described using range (minimum and maximum), mean, SD, and median. Significance of the obtained results was judged at the 5% level. Spearman's coefficient was used to correlate between two abnormally quantitative variables, the F-test (analysis of variance) was used to compare normally quantitative variables between more than two groups, and Pearson's coefficient was used to correlate between two normally quantitative variables.


  Results Top


Data from 184 patients who received cochlear implants at the Audiology Unit, ENT Department, Alexandria University Hospital, between 2000 and 2012, were collected from their records and included sex, age, age of implantation, possible cause of hearing loss, comorbidity, preoperative electrophysiological test results, radiological findings, benefit of speech therapy, and postoperative aided response.

Twenty-five of the 184 patients were examined; data from their records could be collected as mentioned above. All 25 patients had satisfactory aided response postoperatively, and hence they were further subjected to electrophysiological tests and detailed phoniatric evaluation.

Data from all patient records

Statistically significant correlation (P = 0.016) between age of implantation and postoperative pure tone aided response with cochlear implants was found. The earlier the patient is implanted, the better the postoperative average aided thresholds at 500, 1000, 2000 and 4000 tested frequencies are achieved.

No statistically significant correlation (P = 0.729) between mean current unit given to each electrode/number of stimulated electrodes and last aided response was recorded.

Data from the study group

There was no statistically significant difference (P = 0.755) between age of implantation and postoperative grade of benefit from cochlear implant in phoniatric evaluation because the mean age of implantation in the patient groups with different benefits was almost the same: 5.43 ± 1.59 years in those with poor benefit; 5.57 ± 0.75 years in those with fair benefit; and 5.90 ± 1.35 years in those with good benefit.

No statistically significant difference (P = 0.116) between age of implantation and absolute P1 latency values was found because the mean age of implantation in the patient groups with different electrophysiological test results was almost the same: 4.82 ± 1.33 years for no response of P1; mean age of 5.79 ± 1.05 years for good response of P1 waves.

The relation between causes of hearing loss and grade of benefit according to phoniatric evaluation is presented in [Figure 1]. Most of our studied cases had idiopathic prelingual cause with variable outcomes and variable benefit from cochlear implant. No statistically significant difference between possible cause of hearing loss and electrophysiological test results was recorded.
Figure 1 Distribution of possible causes of hearing loss and postoperative benefit of cochlear implantation with regard to phoniatric evaluation in the studied cases. CSOM, chronic suppurative otitis media.

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Statistically significant difference (P = 0.034) between comorbidity [low intelligent quotient (IQ) and epilepsy] and benefit of cochlear implant as regards communicative skills was found. In [Figure 2] statistically significant difference between comorbidity and MMN test results was recorded (P = 0.014), whereas no statistically significant difference between comorbidity and P1 absolute latency was proven (P = 0.064).
Figure 2 Statistically significant difference was found between comorbidity and benefit of cochlear implantation with regard to phoniatric evaluation. All cases of epilepsy and low IQ had poor benefit from cochlear implant. IQ, intelligent quotient.

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[Table 1] shows a statistically significant difference between the benefit of cochlear implant in phoniatric evaluation and electrophysiological test results. Patients with poor benefit from cochlear implant had longer latency of P1 than those with fair and good benefit and 100% of patients with good benefit from cochlear implant in phoniatric evaluation had normal MMN response.
Table 1 Relation between Post-operative benefit of cochlear implant regarding phoniatric evaluation and Obligatory cortical potential absolute latency and Mismatch negativity absolute latency

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  Discussion Top


The present research was designed to evaluate the factors influencing the performance of cochlear implants in patients who received cochlear implants at the Audiology Unit, ENT Department, Alexandria University Hospital, between 2000 and 2012.

To accomplish this aim, data were collected from their records and 25 patients underwent electrophysiological tests and were referred for phoniatric evaluation to estimate the grade of benefit from cochlear implantation as regards communication skills.

The present study found a statistically significant difference between age of implantation and postoperative aided response: the earlier the age of implantation, the better the postoperative average aided thresholds and better benefit from cochlear implants. These findings were supported by Nikolopoulos et al. [16].

Also Holt and Svirsky [8] addressed the question of early implantation and found the same results as those of the present study.

Kirk et al. [17] studied the effects of age at implantation on the development of communication abilities in early-implanted children. The 106 participants were prelingually deafened and used current cochlear implant technology. Results revealed significant improvements in communication skills over time. That is, the earliest implanted children showed more rapid rates of language development, or superior skills overall. Children implanted before the age of 2 years had significantly faster rates of receptive vocabulary and language development compared with later-implanted children. These findings reinforce the importance of the presence of a sensitive or critical period within which development of the auditory system must occur, after which the plasticity of the system is significantly limited.

The present study showed no statistically significant difference between the average current unit given to all working electrodes (whatever the type of implant processor used) and their relation to postoperative average aided thresholds. However, Shannon et al. [18] obtained different results. They found that as the number of electrodes were reduced, performance with cochlear implants gradually decreased across conditions.

In the present study, 89.6% of the prelingual (idiopathic) cause of hearing loss had satisfactory aided response, which is strongly supported by the research of Baudonck et al. [19], who concluded that cochlear implants were the best current alternative for bilateral severe or profound hearing loss, achieving better results in speech perception and development in prelingual children when compared with conventional hearing aids.

Also Fernandes et al. [20] reinforced the benefits of cochlear implants in children with severe or profound hearing loss. However, there is still no consensus among researchers and professionals on whether cochlear implants can improve the hearing skills in children with auditory neuropathy spectrum disorder and in those afflicted with hearing impairment due to meningitis.

Researchers have come to the conclusion that, after cochlear implant surgery, individuals with auditory neuropathy spectrum disorder and meningitis had improved hearing skills, comparable to those of children with sensorineural hearing loss treated with cochlear implant. This does not agree with our study as all examined auditory neuropathy cases had unsatisfactory aided response and 10% of patients with postmeningitis hearing loss had unsatisfactory behavioral pure tone aided response and only 1.9% had satisfactory behavioral pure tone aided response.

The present study showed that there was a statistically significant difference between low IQ and epilepsy and the benefit accruing from cochlear implant in phoniatric evaluation. All cases with comorbidity as such had poor performance in phoniatric evaluation, although their aided thresholds were satisfactory. These results regarding low IQ could not be matched with the results of Lee et al. [21], who studied the performance of children with mental retardation (MR) after cochlear implantation with respect to speech perception, speech intelligibility, and language development. They concluded that children with MR obtain demonstrable benefit from cochlear implantation, and their postoperative performance was tempered by the degree of MR.

Thabet and Said [22] studied cortical auditory evoked potential (P1), a potential objective indicator for auditory rehabilitation outcome. They came to the conclusion that cortical auditory evoked potential (P1) might provide a clinical tool to monitor aural rehabilitation outcome and guide intervention choices.

The present study arrived at the same conclusion by finding a statistically significant difference between the benefit of cochlear implant regarding phoniatric evaluation and electrophysiological test results. Patients with poor benefit from cochlear implants had longer latency of P1 compared with those with fair and good benefit.

‘MMN: a tool for the assessment of stimuli discrimination in cochlear implant patients’ was the title of the research of Wable et al. [23]. Their rationale was that the performance of cochlear implants varies among users.

No relationship between MMN and speech performance was found. A clinical application of this method might be to assess the auditory processing of electrical stimuli in congenitally deaf patients at the preimplantation stage. These results do not match those of the present study, as the present study found a statistically significant difference between speech perception and benefit from cochlear implant and MMN presence or absence within its normal latency: 91.7% of patients with fair benefit and 100% of patients with good benefit had a good and robust MMN response.


  Conclusion Top


We conclude that age of cochlear implantation, possible cause of hearing loss, comorbidity, preoperative electrophysiological test results, and radiological findings are variables affecting cochlear implant performance and outcome. Sex of the patient and number of stimulated electrodes are variables not affecting cochlear implant performance.

Early cochlear implantation and good auditory verbal therapy have better outcomes as regards listening and communication skills. Cortical auditory evoked potential (P1) and MMN might provide a clinical tool to monitor aural rehabilitation outcome. These objective electrophysiological parameters may also be used as prognostic indicators for speech and language outcome.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

 
  References Top

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