What is Cochlear Implant?
Cochlear implant is a biomedical electronic
device that converts acoustic information into electrical current and provides
stimulation directly to the auditory nerve, bypassing damaged hair cells in the
cochlea that prevent sound from reaching. An implant does not result in
"restored" hearing for the recipient, but does allow to perceive
sounds.
Cochlear implant is considered a
safe and effective medical treatment for both children and adults.
History of Cochlear Implant
In 1880, Alesandro Volta First
reported that electrical stimulation to metal rods inserted in his ear canal
created an auditory sensation. In 1957 Eyries placed a wire on the auditory
nerve of someone who was undergoing surgery. This observation lent to the
search for a treatment of profound deafness. In 1961, House and Doyle reported
data from two adults with profound deafness whose auditory nerve was stimulated
electrically by an electrode placed on and then through the round window and
into the scale tympani of the inner ear. In 1964, Simmons placed an electrode
through the promontory into the vestibule and directly onto the odious of the
cochlea.
In the last decade cochlear
implant has developed form speculative laboratory procedure to an accepted
clinical practice. During that period implant device has been developed from
single channel system to more complex multichannel device. The first single channel
cochlear implant was introduced in 1972. The U.S. Food and Drug Administration
(FDA) first approved commercial distribution of the Nucleus 22 multi-channel
device in adult in October 1984 and in children in June 1990.
According to the National
Institute on Deafness and Other Communication Disorders, approximately 25,000
individuals have received cochlear implants in the United States, about half of whom
are adults. More than 70,000 individuals have received cochlear implants
worldwide.
Professor Graeme Clark of the University of Melbourne is the creator and developer
of the world’s first multi-channel implant and is considered by many to be the
father of the cochlear implant. Professor Clark continues to work closely with
Cochlear to bring the gift of hearing to every child and adult who can benefit.
Development of cochlear implant
focuses on:
- Miniaturization. A behind-the-ear (BTE) speech
processor replaced the body-worn processor for approximately 90%. It works
with two 1.4V hearing aid batteries for between seven and twelve days.
Consonant, vowel and sentence testing and patient questioning revealed
that the BTE speech processor demonstrates a significant improvement in
speech understanding compared to the body-worn processor, and that the
patient's device acceptance is superior for the BTE processor.
- Developing the multichannel cochlear implant,
with combined analogue and pulsatile stimulation (CAP). This device is
capable of simultaneously stimulating one electrode with a broadband
analogue signal and the rest of electrode channels with a pulsatile
signal. The system can also be used for purely analogue or for purely
pulsatile stimulation. Preliminary results with the first recipient of a
CAP cochlear implant system demonstrate that the device works as expected.
Parts of Cochlear Implant
All systems are composed of:
- internal, implantable component (receiver/stimular
and electrodes)
- externally worn microphone and processor.
HiRes™ Auria™ Processor Parts:
A - Headpiece - implant.
B - PowerCel - battery.
C - Processor Module -
processing technology that runs the same sound processing software programs as
the pager-style processor.
D - Microphone - interchangeable
input accessory that captures sound in the ear for normal telephone and
headphone use.
How Cochlear Implant Works
Microphone - In this case,
directly located on a behind-the-ear headset.
- picks up sound from the environment,
- sends it to the speech processor.
Sound Processor - which is a
miniaturized computer powered by batteries
- processes sound into digital information (filters,
analyzes and digitizes the sound into coded signals)
- transmits it to the implant over a transmitting
antenna, or headpiece, held in place by magnets in both the headpiece and
implant.
Implant
- converts digital information into electrical signals,
- sends signals down through tiny wires to the
electrode array in the inner ear.
Electrode Array
- delivers electrical signals through tiny contacts, or
electrodes, to the hearing nerve,
- the hearing nerve carries the sound information to
the brain, where it is heard.
There are many different factors
to consider when deciding if a cochlear implant is the right choice. In
general, cochlear implant is a proven medical option for postlingually and
recently prelingually deathened people with severe to profound hearing loss in
both ears and additionally for those who have benefited only minimally from
hearing aids. Cochlear has successfully implanted candidates of different ages
and with differing medical conditions such as Cerebral Palsy, developmental
delays, learning disabilities, diabetes, high blood pressure, tinnitus and
others. It is very important that the implant recipient have an understanding
of a cochlear implant and realistic expectations regarding the use of the
device.
Preoperative Patient Selection
Criteria for Postlinguistlically Deafened Adults:
- Profound sensorineural hearing loss, bilaterally
- Postlinguistically deafened (as defined by acquired
deafness after the age of 5 years)
- Eighteen years of age or older
- Little or no benefit from a hearing aid (as defined
by no open-set speech discrimination when using standardized, recorded
tests)
- No radiological contraindications
- Psychologically and motivationally suitable
- Medical examination should show no contraindications
for undergoing the operative or training procedure
- No deafness due to lesions of the acoustic nerve or
central auditory pathway
- No active middle ear infection
- No absence of cochlear development
The preoperative evaluation
consists of:
- medical/surgical assessments,
- audiological assessments,
- evaluations by other professionals (speech-language
pathologist, psychologist, or social-worker).
Several appointments are required
before a decision is made. A candidate and family are informed about the risks
and benefits of the procedure. It is important that the candidate be
familiarized with the external hardware, counseled, regarding the need for
long-term repair maintenance, and told of the remote risk of internal device
failure. For example, for the Nucleus multichannel device, the internal device
failure rate is less than 2%.
A series of Expectations
Questionnaires have been developed for use with adults who are considering a
cochlear implant (Cochlear Corporation, 1992). The intent of these
questionnaires is to quantify both the prospective candidate’s and the family
member’s expectations of device benefit. If expectations are unrealistically
high, a decision regarding candidacy should be delayed until further counseling
is completed to bring expectations into line.
Medical/Surgical Evaluation
During the initial clinical
visits a clinician obtains detailed medical history and completes otologic
examination. An evaluation has to determine the etiology of the deafness and
establish the age of onset and duration of profound hearing loss. The resurge
found that 21% of the variance in postoperative open-set speech perception
scores was accounted for by the variable of duration of deafness. Other
variables accounted for considerably less variance; however, a number of
factors were identified that, when taken in combination, may allow better
prediction of postoperative performance.
During the physical examination,
it is important to note any potential complicating factors, such as any
previously created surgical defects, congenital anomalies, or other conditions
that could require alterations to the surgical plan. In general, preexisting
ear conditions should be treated prior to final determination of candidacy. A
general physical examination and necessary laboratory tests must be performed
to establish that the patient is healthy enough to undergo surgery without
undue risk.
The most important components of
the medical evaluation is a radiologic assessment of the cochleae. High-
resolution computerized tomography (CT) scans are essential for studying the
structures of the inner ear, specifically the basal turn of the cochlea, and
identifying any malformations or disease processes, such as cochlear
otosclerosis. The results of imaging will be important from the standpoint of
candidate exclusion, ear selection, pre surgical counseling, and general
surgical planning and management.
Contraindications to cochlear
implantation are:
- cochlear agenesis and absence of an auditory nerve,
- cochlear dysplasia,
- partial or complete obliteration of the basal turn of
the cochlea.
When osteoneogenesis is present,
usually the surgeon can drill forward several millimeters in scale tympani
through the new bone and achieve a partial insertion of the electrode array.
The status of the auditory nerve
is evaluated preoperatively by using electrical stimulation of the promontory
or round window. This procedure involves the transtympanic placement of a
needle electrode onto the area of the promontory or, alternatively, placement
of a ball electrode into the round window niche. A small amount of electrical
current is passed between the stimulating electrode and a surface electrode
that is placed on the ipsilateral cheek or earlobe. The patient should report a
consistent hearing sensation that is time-locked to the presentation of the
stimulus and in creases in intensity as current is increased.
Individuals who do not exhibit
responses to promontory or round window stimulation are generally not
considered candidates for cochlear implantation, as a negative result suggests
there is an insufficient number of remaining auditory nerve fibers to elicit a
hearing perception. Promontory or round window stimulation may not be indicated
in all cases. If a candidate demonstrates low-frequency auditory thresholds
that are described as hearing rather than tactile, it may not be necessary to
perform a promontory test. Whenever there is concern regarding the integrity of
the auditory nerve when the patient exhibits a total hearing loss in the ear
that is being considered for implantation, promontory stimulation should be
performed. Promontory testing is essential when the deafness is due to head
trauma, as it is possible that fracture of the temporal bone could be
concomitant with severing of the acoustic nerve.
Level I:
Air/Bone Conduction Audiometry
and Immittance Testing.
The audiological assessment
consists of measurements of residual hearing and middle ear function,
bilaterally.
Air-conduction thresholds should
be determined for the frequencies ranging from 125 to 8000 Hz using a
calibrated audiometer that has an output greater than 115 dB at 500 through
4000 Hz.
Bone-conduction is performed to
rule out a significant conductive component.
Immittance testing is performed
to rule out a significant conductive component.
Stapedial reflex test findings
should be consistent with a profound sensorineural hearing loss. Most commonly,
reflexes will be absent at frequencies above 250 Hz for those with profound
sensorineural hearing loss, bilaterally. If reflexes are obtained at
frequencies above 250 Hz, auditory brainstem response testing should be
performed to rule out a nonorganic component to the hearing loss. Stimuli
should consist of both unfiltered clicks and frequency-specific tone pips to
ascertain the general configuration of the hearing loss.
Level II:
Aided Audiometric and Speech
Testing.
Once a profound bilateral
sensorineural hearing loss has been determined, the degree of benefit obtained
from amplification is measured. First, a hearing aid evaluation should be
conducted to establish whether the candidate’s hearing aids are appropriate for
the degree of hearing loss. If it is determined that alternative amplification
would be more appropriate, a trial period is recommended. For
postlinguistically deafened adults, a trial with a tactile device is not
recommended because of the limited benefit derived by currently available
technology.
The hearing aid evaluation
should consist of:
- Standard electroacoustic measurements.
- Soundfield warble-tone thresholds should be carried
out in a monitored environment, using a measuring microphone attached to a
sound-level meter. The candidate is seated facing a loudspeaker in a
sound-treated room at a distance of 1 meter. The measuring probe
microphone should be placed in close proximity to the hearing aid
microphone. Warble-tone thresholds are assessed at frequencies ranging
from 250 to 4000 Hz, and a speech detection threshold is obtained.
Assessment of speech ability
The speech discrimination test
battery is administered in the best-aided condition, unless there is more
residual hearing in one ear, warranting a monaural workup to assess the
contribution of each ear to the binaural listening condition. In this case, a
screening test that measures monaural and binaural open-set sentence
recognition is recommended prior to the complete evaluation.
The speech perception battery
typically includes closed- and open-set measures and an assessment of
speechreading ability. Recorded materials are recommended over live-voice
presentations so that results can be compared across cochlear implant centers
and for a give patient overtime. A thorough test battery, referred to as the
Minimal Auditory Capabilities (MAC) battery, was designed by Owens and his
colleagues (1985) for postlinguistically deafened adults with profound hearing
loss.
It includes 14 subtests that
evaluate:
- perception of suprasegmental and segmental aspects of
speech,
- environmental sounds recognition,
- speechreading enhancement.
The battery includes both easier
closed-set and more difficult open-set measures.
When the medical and audiologic
assessments are completed, the cochlear implant team should discuss the
candidate’s preoperative profile. The medical findings are reviewed; paying
close attention to the results of the high-resolution CT scans. The audiologic
findings are discussed in relation to the potential for postoperative benefit
based on findings from a large pool of implant recipients.
Procedures of evaluating efficiency of cochlear implant
Hearing sounds without hearing aid
Hearing sounds with hearing aid
Improvement in acuity level and
SAT
The benefits of cochlear
implantation have to be weighed carefully against eventual adverse effects.
The present multi-centric study
involved 19 centres, 16 of them in German speaking countries, 1 British, 1
Polish and 1 Hungarian. 60 post-lingually deafened adults with a mean age of
47.5 years (20-70) and mean duration of deafness 5.3 years (0.5-20) have been
evaluated with the MED-EL COMBI 40 cochlear implant which implements a
high-rate continuous-interleaved-sampling strategy with 8 channels. Safety and
effectiveness data have been collected. Speech perception tests include a 16-consonant,
an 8-vowel, a sentence and a monosyllabic word test in all languages and a
2-digit figure test in all languages but English. Test intervals are 1, 3, 6
months and 1 year after first fitting. 41 of the 60 post-lingually deafened
adult study patients have completed their 6-month evaluation. While their
pre-operative monosyllabic word score was 0%, their mean monosyllabic word
score 6 months after first fitting was 48% (8-90) with a median of 50%. The
mean sentence understanding was 84% (24-100) with a median of 90%. The
respective values for the 1-year evaluations with 25 patients are a mean of 50%
(5-85), with a median of 60% for the monosyllables and a mean of 89% (30-100),
with a median of 97% for the sentences.
The most important aim of a cochlear
implant usually is to achieve speech understanding. Music-perception is also an
aspect of hearing that can be considered as a contribution to the total benefit
a patient gains from his implant…The first results from implant users show a
tendency that temporal features, like the ones discriminating different
rhythms, can be perceived better than features related to pitch, like expressed
discrimination and recognition of tunes or different musical instruments.
Programming system
Each speech processor is
programmed to meet individual’s hearing needs. Different speech coding
strategies emphasize different pitch, loudness and timing cues. The brain
receives information within microseconds of the microphone picking up sound, so
individual hears sounds as they occur.
The programming system includes
IBM PC-compatible computer, two computer interface cards, an interface unit,
the necessary cabling, and customized software.
4- to 6-weeks after the surgical
placement the cochlear implant recipient returns for the fitting. The first
step is to program the speech processor. Customized software is used to perform
specific psychophysical tests. The most important measurement is a determination
of the electrical dynamic range of hearing for each electrode pair. This is
accomplished by establishing:
- the threshold and
- the maximum comfortable loudness level for electrical
stimulation. Electrical dynamic ranges are on the order of 6 to 25 dB. The
software automatically assigns a frequency range to each electrode that
will be used in the MAP.
Auditory Training
Following the fitting of the
external equipment, an individualized program of auditory training should be
initiated. The length of this training will vary for each individual, extending
from 4 to 10 weeks for a postlinguistically deafened adult, to long-term
habilitation for a prelinguistically deafened child. It is important to begin
auditory training at a level wherein the tasks are not too difficult for the
individual.
In this way, progress can be
based on achievements, and discouragement on the patient’s part can be
minimized. Screening tests can be used to determine the level where an
individual should begin his or her training.
As with any medical procedure,
the results of implantation cannot be predicted prior to surgery and recipients
may experience a wide range of outcomes. For individuals who lost their hearing
after learning to speak, the perception of speech and sounds after implantation
may initially seem quite different from what they remember. After using the
cochlear implant for several months or more, these individuals often report
that they perceive speech to be more natural or closer to their memory of
familiar sounds.
Training phases
Training begins with speech
stimuli presented in an auditory-visual context.
After success auditory-only
speech material may be introduced.
Initially, this material is
presented in a closed- set format; later, contextually based open- set material
can be used.
Historically, both analytic and
synthetic speech materials have been employed.
A. The analytic materials were
vowels and consonants presented in a nonsense syllable paradigm in three
conditions:
- speechreading only,
- speechreading plus hearing,
- hearing only.
B. The synthetic task was
continuous discourse speech tracking.
The clinician verbally sends contextual
material to the patient. The patient was required to repeat it back verbally
with 100% accuracy. A number of prompts and strategies were used to assure 100%
reception of the information by the listener. Results were described as the
number of words per minute correctly received by the listener. Several
investigators have noted that the tracking rate was influenced by the
familiarity with and level of difficulty of the material, the speaking rate of
the clinician and the patient, and the types of strategies and prompts used.
Professionals who compose the
implant team?
Among the professionals who may
work as part of the cochlear implant team are audiologists, speech-language
pathologists, educators, surgeons, medical specialists, psychologists and
counselors.
Audiologists are involved in many
of the components of the cochlear implant program, including determining the
candidacy of an individual for implantation, as well as activating and
programming of the speech processor after surgery. Both audiologists and
speech-language pathologists provide aural rehabilitation services to implant
recipients to facilitate their ability to detect and understand speech with the
cochlear implant. Aural rehabilitation services may include processes to
enhance communication, auditory training and speechreading, training on the use
and care of the implant, and support of the needs of the recipient and family.
The costs of cochlear implants
vary widely depending on a number of factors, including the duration and extent
of a patient’s hearing loss prior to surgery. The average cost for the entire
procedure, including the post-operative aural rehabilitation process, exceeds $40,000.
Medicare, TRICARE, the Veteran’s
Administration, and all other federal health plans provide benefits for all
cochlear implant services. Federal law requires that all state Medicaid
agencies provide coverage for cochlear implant for children under 21 years old,
and most provide benefits for adults as well. Vocational rehabilitation,
maternal and children’s health services, and other combined federal-state
programs also often provide benefits.
Manufacturers approved by FDA to distribute Cochlear Implants in the
U.S.
Residual Hearing after Cochlear
Implantation. Presented at the Second Cong. of Asia
Pacific Symp. on Cochlear Implant and Rel. Sci., 1999
Alpiner, J, McCarthy, P (1993)
Rehabilitative Audiology: Children and Adults, Williams & Wilkins, 417 –
437
Hochmair-Desoyer IJ, Zierhofer C,
Hochmair ES (1993) New hardware for analogue and combined analogue and
pulsatile sound-encoding strategies, Prog Brain Res, 97: 291-300
Sorkin D.L, (2002). Cochlear
implant candidacy and outcomes: 2002 Update. Hearing Loss: The Journal of Self
Help for Hard of Hearing People.
Kiefer J, von Illberg C et al.
(1998). Results of cochlear implantation in patients with severe to profound
hearing loss- implications for patient selection. Audiology, 37(6): 382-395
Alpiner, J, McCarthy, P (1993)
Rehabilitative Audiology: Children and Adults, Williams & Wilkins, after A.
L. Beiter, J. A. Brimacombe, Cochlear Implants, p.421
Gerfand, S. A.(1997).Essential of
Audiology, Second Edition. NY: Thieme
University of Iowa
Cochlear Implant Project, Gantz (1992)
Gerfand, S. A.(1997).Essential of
Audiology, Second Edition. NY: Thieme
Gerfand, S. A.(1997).Essential of
Audiology, Second Edition. NY: Thieme
Gerfand, S. A.(1997).Essential of
Audiology, Second Edition. NY: Thieme
Helms J, Müller J, Schon F, Moser
L, Arnold W, Janssen T, Ramsden R, von Ilberg C, Kiefer J, Pfennigdorf
T,Gstöttner W, Baumgartner W, Ehrenberger K, Skarzynski H, Ribari O, Thumfart
W, Stephan K, Mann W, Heinemann M, Zorowka P, Lippert KL, Zenner HP, Bohndord
M, Hüttenbrink K, Hochmair-Desoyer I et al. (1997). Evaluation of performance
with the COMBI40 cochlear implant in adults: a multicentric clinical study.
ORL, 59: 23-35
Schulz E, Kerber M (1994). Music
perception with the MED-EL implants. In Advances in Cochlear Implants, Eds.
Hochmair-Desoyer IJ, Hochmair ES, Wien, 326-332
Gerfand, S. A.(1997).Essential of
Audiology, Second Edition. NY: Thieme
Hochmair-Desoyer IJ, Zierhofer C,
Hochmair ES (1993) New hardware for analogue and combined analogue and
pulsatile sound-encoding strategies, Prog Brain Res, 97: 291-300
Schmidt M, Griesser A (1997)
Long-Term stability of fitting parameters with the COMBI40. The American
Journal of Otology, 18 (suppl 6)
Gerfand, S. A.(1997).Essential of
Audiology, Second Edition. NY: Thieme
Residual Hearing after Cochlear
Implantation. Presented at the Second Cong. of Asia
Pacific Symp. on Cochlear Implant and Rel. Sci., 1999
American Speech-Language-Hearing
Association. (2004) Position Statement: Cochlear Implants. ASHA Supplement 24,
in press Advanced Bionics
Journal Articles:
American Speech-Language-Hearing
Association. (2004) Guidelines: Cochlear Implants. ASHA Supplement 24, in
press.
American Speech-Language-Hearing
Association. (2004) Position Statement: Cochlear Implants. ASHA Supplement 24,
in press.
American Speech-Language-Hearing
Association. (2004) Technical Report: Cochlear Implants. ASHA Supplement 24, in
press.
Comparison of performance of the
MED-EL body worn speech processor CIS PRO+ with the new MED-EL BTE processor
TEMPO+ in adults. Presented at the Second Cong. of Asia
Pacific Symp. on Cochlear Implant and Rel. Sci., 1999
Helms J, Müller J, Schon F, Moser
L, Arnold W, Janssen T, Ramsden R, von Ilberg C, Kiefer J, Pfennigdorf
T,Gstöttner W, Baumgartner W, Karinen PJ., Sorri M..J., Valimaa T. T., Hüttunen
KH, Löpponen HJ (2001) Cochlear implant patients and quality of life, Scand
Audiol Suppl, 52: 48-50
Kiefer J, von Illberg C et al.
(1998). Results of cochlear implantation in patients with severe to profound
hearing loss- implications for patient selection. Audiology, 37(6): 382-395.
Residual Hearing after Cochlear
Implantation. Presented at the Second Cong. of Asia
Pacific Symp. on Cochlear Implant and Rel. Sci., 1999
Schmidt M, Griesser A (1997)
Long-Term stability of fitting parameters with the COMBI40. The American
Journal of Otology, 18 (suppl 6).
Schulz E, Kerber M (1994). Music
perception with the MED-EL implants. In Advances in Cochlear Implants, Eds.
Hochmair-Desoyer IJ, Sorkin D.L, (2002). Cochlear implant candidacy and
outcomes: 2002 Update. Hearing Loss: The Journal of Self Help for Hard of
Hearing Hochmair E S, Wien, 326-332.
Textbook Chapters:
Alpiner, J, McCarthy, P (1993).
Rehabilitative Audiology: Children and Adults, Williams & Wilkins
Gerfand, S. A.(1997).Essential of
Audiology, Second Edition. NY: Thieme.
Hochmair-Desoyer IJ, Zierhofer C,
Hochmair ES (1993) New hardware for analogue and combined analogue and
pulsatile sound-encoding strategies, Prog Brain Res, 97: 291-300.
Hüttenbrink K, Hochmair-Desoyer I
et. al. (1997). Evaluation of performance with the COMBI40 cochlear implant in
adults: a multicentric clinical study. ORL, 59: 23-35.
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