Web Posted on: February 24, 1998

COCHLEAR IMPLANTS: THE IMPLANT AND THE REHABILITATION

Denise L. Lux
Cochlear Corporation
61 Inverness Drive East, Suite 200
Englewood, CO 80112
Voice/Message: (309)266-8651
FAX: (309)266-8654
Internet:dlux@cochlear.com

Robert B. Mahaffey
IBM Special Needs
11400 Burnet Rd.
Austin, TX 78758
Voice/Message: (512)838-4597
FAX: (512)838-9367
Internet:bmahaffe@us.ibm.com

A cochlear implant is an electronic device designed to provide sound information for adults and children who have a sensorineural hearing loss ("nerve deafness") in both ears and obtain limited benefit from appropriate binaural hearing aids. In adults deafened before learning speech and language (prelinguistically deafened) and in children, the loss must be profound. In postlinguistically deafened adults, the loss may be severe-to-profound or profound.

In 1957, the first research on cochlear implants began in France. Since then, cochlear implant technology has evolved from a device with a single electrode (or channel) to systems that transmit more sound information through multiple electrodes (or channels).

More than 17,000 people worldwide have received cochlear implants. More than 15,000 of those individuals worldwide have obtained a Nucleus cochlear implant system, including over 6,500 children. Worldwide, the Nucleus system is the most frequently prescribed cochlear implant for children and adults.

Hearing aids and some assistive listening devices simply amplify sound; i.e., make it louder. However, sounds provided by even the most powerful and sophisticated hearing aids may not offer much useful benefit to those with a severe-to-profound or profound hearing loss in both ears.

A cochlear implant, on the other hand, is designed to provide useful sound information by directly stimulating the surviving auditory nerve fibers in the inner ear (cochlea). Candidates for the Nucleus Spectra 22 Cochlear Implant System include adults and children who meet the following criteria:

General Criteria for a Spectra 22 System

Adults (18 years of age or older)

• Profound or severe-to-profound sensorineural hearing loss ("nerve deafness") in both ears.
• Hearing loss acquired after learning oral speech and language ("postlinguistic" hearing loss)
• Limited benefit from appropriate hearing aids; i.e., a score of 30% or less on sentence recognition tests in the best-aided listening condition. No medical contraindications
• A desire to be part of the hearing world

( Prelinguistically deafened adults with a profound loss bilaterally should be evaluated be experienced cochlear implant teams and have their candidacy determined on a case-by-case basis.)

Children

• Profound sensorineural hearing loss ("nerve deafness") in both ears 2 through 17 years of age
• Little or no useful benefit from hearing aids
• No medical contraindications
• High motivation and appropriate expectations (both child and family)
• Placement in an educational program that emphasized development of auditory skills after the implant that has been fitted

The Nuclues Spectra 22 Cochlear Implant system consists of the following internal and external components:

The internal components are surgically implanted completely under the skin, and include:

• A receiver/stimulator that is positioned under the skin in a shallow "bed" made in the bone behind the ear.
• The receiver/stimulator is attached to an electrode array.
• The flexible biocompatible electrode array, consisting of 22 tiny electrode bands, is inserted approximately one inch into the cochlea.

The external components worn by the individual incorporate:

• The Spectra 22 speech processor, which looks like a pocket calculator and weighs only 3.5 ounces.
• A headset, including:

##a directional front-facing microphone that looks, and is worn, like a small behind-the-ear hearing aid.

##a transmitting coil, about one inch in diameter, that is held in place behind the ear over the implanted receiver/stimulator by small magnets in both the transmitting coil and receiver/stimulator.

##two cables (cords) that connect together the microphone, speech processor and transmitting coil.

The Spectra 22 system transmits sound information in the following way:

1. Sounds in the environment are picked up by the small directional microphone.
2. A thin cable (cord) sends the sound from the microphone to the Spectra 22 speech processor, a powerful miniaturized computer.
3. The speech processor filters, analyzes and digitizes sound into coded signals.
4. These coded signals are sent from the speech processor to the transmitting coil via the cables.
5. The transmitting coil sends the signals across the skin to the implanted receiver/stimulator via an FM radio signal (no plug or wires go through the skin).
6. The receiver/stimulator delivers the correct amount of electrical stimulation to the appropriate electrodes on the array.
7. The electrodes along the array stimulate the remaining auditory nerve fibers in the cochlear.
8. The resulting electrical sound information is sent through the auditory system to the brain for interpretation.

The Nucleus Spectra 22 Cochlear Implant System sets the standard. Although no cochlear implant can restore normal hearing, the following benefits are based on scientific data collected during U.S. - regulated clinical trials at multiple research centers. Benefits for Those Using a Nucleus Implant System

Postlinguistic Adults(##)

• Adults are able to hear conversation and environmental sounds at comfortable loudness levels.
• Almost all adults improve their communication abilities when using the implant in conjunction with lipreading.
• Adults are able to understand speech in quiet and noise without lipreading (these benefits are described on the following pages). Some adults have a limited ability to use the telephone.

Children

• Children are able to detect conversational level sounds, including speech, at comfortable loudness levels.
• Some($$) children can identify everyday sounds, such as car horns, doorbells and birds singing, from a set of alternatives. Many children can distinguish among different speech patterns.
• Many children can identify words from a set of alternatives without lipreading.
• Some children exhibit improved lipreading.
• A few children can recognize speech without lipreading.
• After training and experience with the device, many children demonstrate improvements in speech.

(##)NOTE: Prelinguistically deafened adults demonstrate limited benefit from a cochlear implant. Many improve in detection of sound, but only a few demonstrate improved lipreading after extensive training. Prelinguistically deafened adults who do not have functional oral speech and language and are not motivated to participate in rehabilitation, are more likely to become nonusers of the device than other adults.

($$)NOTE: When the words "few", "some" and "many" are used, they represent the following percentage of children who participated in clinical trials: Few - greater than 5% and equal to or less than 34%

Some - greater than 34%, less than 52%

Many - equal to or greater than 52%

The latest results with the Spectra 22 system reflect the enhanced performance of postlinguistically deafened adults who use the SPEAK coding strategy. A summary of the results are listed below:

Adults who were implanted consecutively.

The following chart summarizes the open-set (unrehearsed) sentence recognition abilities in quiet of a consecutive (in selected) group of adults implanted with the Spectra 22 system and using the SPEAK coding strategy.

Performance in quiet

Average = 71%

Median = 83%

Scores in quiet for open-set words in sentences 51 consecutively implanted adults(##)

• 92% of recipients recognized 20% or more
• 86% recognized more than 30%
• 50% recognized 83% or more
• 27% recognized 96% or more
• 8% recognized less than 20%

(##)NOTE: The above statements summarize the sound field postoperative open-set sentence recognition abilities of 51 adults with profound or severe-to-profound postlinguistic sensorineural hearing loss. The 51 adults were implanted consecutively at eight centers in the United States and Australia, and had been using the Nucleus implant with the Spectra 22 Speech Processor between two weeks and six months at the time of testing. The test material consisted of tape-recorded CID Sentences, presented in quiet at 70 dB SPL through a loudspeaker positioned directly in front of the patients (00 azimuth). Individual subject results were analyzed using a binomial statistical model.

When a person is interested in obtaining a cochlear implant, the implant center will conduct a careful evaluation to determine whether the individual is an appropriate cochlear implant candidate. The evaluation process can be stopped at any time if you, your child, or the implant team feels it is not appropriate to continue.

Several evaluations are conducted, including:

• audiological evaluations to determine the level of hearing loss.
• a hearing aid evaluation or trial use of high-powered hearing aids to determine if amplification will provide adequate benefit.
• medical evaluation to determine if:

##the cochlea is suitable for an implant.

##the candidate can safely undergo general anesthesia and surgery.

##other medical conditions exist that would preclude use of an implant.

• discussions and, when necessary, psychological assessment to ensure that the candidate and family are highly motivated and have realistic expectations.
• educational assessments for children.

If the candidate and the team agree to proceed with implantation procedures, members of the team will:

• assist in determining insurance coverage.
• perform the surgery.
• fit and activate the implant system after the incision has healed, and help the recipient obtain the most benefit from the device.

At the time of surgery, the receiver/stimulator and the electrode array - are implanted totally underneath the skin. The surgery usually takes 2-3 hours and is often conducted as an outpatient procedure.

1. Prior to surgery, the area of the hear where the implant will be placed is shaved.
2. While the individual is under general anesthesia, the surgeon makes an incision behind the ear.
3. The surgeon then forms a small depression in the mastoid bone behind the ear to hold the receiver/stimulator in place.
4. The electrode array is inserted into the cochlea through an opening near the round window. The thin, tapered, and flexible construction of the electrode array minimizes damage during insertion and helps it conform to the cochlea's curved shape.
5. The incision is then closed and the head bandaged. Once the skin heals, the internal parts of the implant are invisible; the only visible evidence is a small bump, which generally can be covered by hair.

It generally takes 3-5 weeks after surgery for the incision to heal. However, most implant recipients feel well enough during that time to resume their normal activities.

After the incision has healed, the recipient returns to the clinic for initial fitting of the external implant components: the microphone, headset, speech processor and connecting cables (cords). The clinician programs the speech processor, setting the appropriate levels of stimulation for each electrode from soft to comfortably loud. The program can easily be adjusted as the user becomes accustomed to the new sound information.

In rare cases, all of the electrodes may not be available. In that case, the clinician can eliminate specific electrodes from the program in the speech processor so that only those electrodes that provide appropriate and comfortable auditory information are used. The full speech sound spectrum will still be transmitted by the implant system, although the information will be less refined because fewer electrodes will be responsible for transmitting more of the sound information.

After an individual receives a cochlear implant, intensive aural rehabilitation is required. For postlingually adults, this is typically provided by an audiologist or speech language pathologist. It involves relearning how to decode sounds including speech. It also involves readjusting to the world around them. The clinician works with adults on communication strategies, coping strategies, appropriate expectations, speech understanding and speech production as needed. For postlingually deafened children (over the age of five years), the approach is very similar.

Aural habilitation provided to prelingually deafened children, may be provided by an audiologist, a speech language pathologist or a teacher for the deaf/hard of hearing. Since these children have never heard before, the clinician's task is much more challenging. The clinician must help make sound meaningful to the children. She must assist in attaching meaning to the environmental sounds as well as the speech and language that the child is hearing. In addition, the clinician must support the child in learning to function in the "hearing world" by teaching appropriate communication techniques and pragmatic responses. The clinicians for the population are increasing choosing to use technology, such as software programs, to facilitate the intervention they provide.

The cochlear implant process, from evaluation to surgery to rehabilitation is a long and challenging process but one thousands of children and adults worldwide have felt is well worth the effort!