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Medical Encyclopedia:

Cochlear Implants

Definition

A cochlear implant is a surgical treatment for hearing loss that works like an artificial human cochlea in the inner ear, helping to send sound from the ear to the brain. It is different from a hearing aid, which simply amplifies sound.

Description

Hearing loss is caused by a number of different problems that occur either in the hearing nerve or parts of the middle or inner ear. The most common type of deafness is caused by damaged hair cells in the cochlea, the hearing part of the inner ear. Normally, hair cells stimulate the hearing nerve, which transmits sound signals to the brain. When hair cells stop functioning, the hearing nerve remains unstimulated, and the person can't hear. Hair cells can be destroyed by many things, including infection, trauma, loud noise, aging, or birth defects.

All cochlear implants consist of a microphone worn behind the ear that picks up sound and sends it along a wire to a speech processor, which is worn in a small shoulder pouch, pocket, or belt. The processor boosts the sound, filters out background noise, and turns sound into digital signals before sending it to a transmitter worn behind the ear. A magnet holds the transmitter in place through its attraction to the receiver-stimulator, a part of the device that is surgically attached beneath the skin in the skull. The receiver picks up digital signs forwarded by the transmitter, and converts them into electrical impulses. These electrical impulses flow through electrodes contained in a narrow, flexible tube that has been threaded into the cochlea.

As many as 24 electrodes (depending on the type of implant) carry the impulses that stimulate the hearing nerve. The brain then interprets the signals as specific sounds.

Despite the benefits that the implant appears to offer, some hearing specialists and members of the deaf community still believe that the benefits may not outweigh the risks and limitations of the device. Because the device must be surgically implanted, it carries some surgical risk. Also, manufacturers can't promise how well a person will hear with an implant. Moreover, after getting an implant, some people say they feel alienated from the Deaf community, while at the same time not feeling fully a part of the hearing world.

The sounds heard through an implant are different from the normal hearing sounds, and have been described as artificial or "robotlike." This is because the implant's handful of electrodes cannot hope to match the complexity of a person's 15,000 hair cells.

Surgical procedure

During the procedure, the surgeon makes an incision behind the ear and opens the mastoid bone (the ridge on the skull behind the ear) leading into the middle ear. The surgeon then places the receiver-stimulator in the bone, and gently threads the electrodes into the cochlea. This operation takes between one and one-half to five hours.

— Carol A. Turkington



 
 
Dictionary: cochlear implant

n.

An electronic apparatus that allows people with severe hearing loss to recognize some sounds, especially speech sounds, and that consists chiefly of a microphone and receiver, a processor that converts speech into electronic signals, and an array of electrodes that transmit the signals to the auditory nerve in the inner ear.


 
Surgery Encyclopedia: Cochlear Implants

Definition

A cochlear implant is a small, complex electronic device used to treat severe to profound hearing loss. It is surgically implanted underneath the skin behind the patient's ear.

Purpose

A cochlear implant delivers useful auditory signals from the environment to the patient by electronically bypassing nonfunctional parts of the ear and directly stimulating the auditory nerve. Unlike a hearing aid, it does not merely amplify sound. Instead, an implant increases the amount of nervous response to sound. Although it does not restore normal hearing, the additional input provided by the implant often improves sound detection and increases speech understanding.

Description

Normal hearing occurs because sound travels from the outer ear into the ear canal and vibrates the eardrum. The vibration is carried through the middle ear by three small bones attached to the eardrum and on to a fluid-filled part of the inner ear called the cochlea. Movement in the cochlear fluid is transferred to hair fibers within the cochlea. The movement of these hair cells stimulates nerve cells called ganglion cells that send an electrical current to the auditory nerve. In turn, the nerve carries the current to the brain, where the electrical stimulation is recognized as sound.

A common cause of hearing loss is damage to the hair cells within the cochlea. This kind of deafness, called sensorineural deafness, can often be treated with cochlear implants. This is particularly true if damage to the hair cells is not accompanied by damage to the auditory nerve itself. As of 2002, it is estimated that over 35,000 individuals have received cochlear implants.

Cochlear implants consist of internal and external parts. The external parts include a microphone, a speech processor, and a transmitter. The internal parts include a receiver-stimulator and an electrode. Some models include a small headpiece that is worn just behind the ear and contains all the external parts while other models also use body-worn modules that are placed in a shoulder pouch, in a pocket, or worn on a belt. The convenience of the all-in-one headpiece is balanced by shorter life for the batteries used in the smaller units, although systems using rechargeable batteries do solve some of these issues.

Within the headpiece, the microphone picks up sound in the environment. The speech processor converts these sounds into a digital signal. The content of the generated digital signal is determined by the programming of the processor and is complex. It includes information about the pitch, loudness, and timing of sound signals and attempts to filter out extraneous noise. The transmitter converts the digital signals into FM radio signals and sends them through the skin to the internal parts of the implant. The transmitter and the internal parts are kept in correct alignment by using magnets present in both the internal and external parts of the device.

The internal parts are those that are surgically implanted into the patient. The receiver-stimulator is disk-shaped and is about the size of a quarter. It receives the digital signals from the transmitter and converts them into electrical signals. A wire connects the receiver to a group of electrodes that are threaded into the cochlea when the implant is placed. As many as 24 electrodes, depending on the type of the implant, stimulate the ganglion cells in the cochlea. These cells transmit the signals to the brain through the auditory nerve. The brain then interprets the signals as sound.

The sounds heard through an implant are different from the normal hearing sounds and have been described as artificial or robot-like. This is because the implant's handful of electrodes cannot hope to match the complexity of a person's 15,000 hair cells. However, as more electrodes are added, electrode placement issues are solved, and the software for the implant speech processor takes into account more and more aspects of sound, the perceived results are moving closer to how speech and other sounds are naturally perceived.

Despite the benefits that the implant appears to offer, some hearing specialists and members of the deaf community believe that the benefits may not outweigh the risks and limitations of the device. Because the device must be surgically implanted, it carries some surgical risk. Manufacturers can not promise how well a person will hear with an implant. Moreover, after getting an implant, some people say they feel alienated from the

A cochlear implant has a microphone outside the ear that transmits sounds to an implanted receiver. In turn, the receiver transmits electrical impulses to the cochlea and cochlear nerve, which is stimulated in normal hearing. (Illustration by GGS Inc.)

A cochlear implant has a microphone outside the ear that transmits sounds to an implanted receiver. In turn, the receiver transmits electrical impulses to the cochlea and cochlear nerve, which is stimulated in normal hearing. (Illustration by GGS Inc.)

deaf community, while at the same time not feeling fully a part of the hearing world. The decision to undergo cochlear implant surgery is a complex one and a person should take into account the risks and realistic rewards of the device.

Surgical Procedure

The procedure can be preformed on an outpatient basis for adult and adolescent patients. With children, it is often performed with a one-night stay in the hospital.

The internal parts of the implant are placed under the skin behind the patient's ear. The area is shaved, although newer procedures allow for sterilization of the hair in the area so less shaving has to occur. Once the sterile field is established, the surgeon makes an 2–3 in (5–7.6 cm) incision behind the ear and opens the mastoid bone (the ridge on the skull behind the ear) leading into the middle ear. A depression is made in the bone next to the opening to allow the receiver-stimulator to sit flush with the skull surface. After seating, the receiver-stimulator is held in place with a long-lasting suture.

The surgeon then goes through the opening in the mastoid bone to create a new opening in the cochlea for the implant electrodes. The electrode is then very slowly and careful threaded through this new opening. Care is taken during the procedure, and the electrode structure itself is designed to align the electrodes as closely as possible to the ganglion cells, as this allows the electrical signals that function to be less powerful. Once in place, the device is tested to be certain it is working. If all is well, the surgeon then closes up the incision with absorbable sutures, so the area does not need to be revisited to remove the stitches.

The entire operation takes between one and two hours, although the procedure is more complex for younger patients due to the smaller size of their middle ear structures and tends to take longer.

Aftercare

For a short period of time after the surgery, a special bandage is worn on the head during sleep. After about one month, the surgical wounds are healed and the patient returns to the implant clinic to be fitted with the external parts of the device and to have the device turned on and mapped. Mapping involves fine tuning the speech processor and setting levels of stimulation for each electrode, from soft to loud.

The patient is then trained in how to interpret the sounds heard through the device. The length of the training varies from days to years, depending on how well the person can interpret the sounds heard through the device.

Risks

As with all operations, there are risks with this surgery. These include:

  • infection at the incision site
  • bleeding
  • complications related to anesthesia
  • transient dizziness
  • facial paralysis (rarely)
  • temporary taste disturbances
  • additional hearing loss
  • device failure

However, it should be noted that serious surgical complications have been observed at only one in 10,000 procedures of this type.

Some long-term risks of the implant include the unknown effects of electrical stimulation on the nervous system. It is also possible to damage the implant's internal components by a blow to the head, which will render the device unworkable.

A further consideration is that the use of magnetic resonance imaging (MRI) for patients with cochlear implants is not recommended because of the magnets present in the devices. Several companies have developed implants that do not use magnets or have altered the receiver-stimulator make up to make it easier to remove the magnets before testing. One fact that reduces the concern about MRI testing is that for many medical indications, MRI can be replaced with a computer assisted tomography scan (CAT or CT scan), which is not a problem for persons with cochlear implants.

Additionally, in July 2002, the Food and Drug Administration (FDA) issued a warning about a possible connection between increased incidence of meningitis and the presence of a cochlear implant. This warning included special vaccine recommendations for those with implants, as well as the voluntary removal from the market of certain devices. Specifically, those implants that included a positioner to hold the electrodes in place in the cochlea appear to be associated with an increased risk of the disease.

Normal Results

Most profoundly deaf patients who receive an implant are able to discern medium and loud sounds, including speech, at comfortable listening levels. Many use sound clues from the implant, together with speech reading and other facial cues, to achieve understanding. Almost all adults improve their communication skills when combining the implant with speech reading (lip reading), and some can understand spoken words without speech reading. More than half of adults who lost hearing after they learned to speak can understand some speech without speech reading. Especially with the use of accessory devices, the great majority can utilize the telephone with their implants.

Children who were born deaf or who lost their hearing before they could speak have the most difficulty in learning to use the implant. Research suggests, however, that most of these children are able to learn spoken language and understand speech using the implant. In general, the earlier the implant occurs the greater the chance of the implant providing sufficient sound input to provide speech understanding. As with the use of the telephone in adults, accessory devices such as special microphones often help the function of the implant in classroom settings.

Resources

Books

Christiansen, John B. and Irene W. Leigh. Cochlear Implants inChildren: Ethics and Choices. Washington, DC: Galladet University Press, 2002.

Niparko, John K., ed. Cochlear Implants: Principles and Practices. Philadelphia: Lippincott, Williams & Wilkins, 2000.

Periodicals

Cheng, Andre K., et al. "Cost-Utility Analysis of the Cochlear Implant in Children." Journal of the American Medical Association 284, no. 7 (August 16, 2000): 850–856.

"The Earlier the Implant, the Greater the Benefit." The HearingJournal (February 2001).

Mraz, Stephen J. "Breaking the Wall of Silence." Machine Design (December 9, 1999).

Organizations

Alexander Graham Bell Association for the Deaf. 3417 Volta Place NW, Washington, DC 20007. (202) 337-5220. http://www.agbell.org.

Cochlear Implant Club International. 5335 Wisconsin Ave. NW, Suite 440, Washington, D.C. 20015-2052. (202) 895-2781. http://www.cici.org.

Hearing Loss Link. 2600 W. Peterson Ave., Ste. 202, Chicago, IL 60659. (312) 743-1032, (312) 743-1007 (TDD).

National Association for the Deaf. 814 Thayer Ave., Silver Spring, MD 20910. (301) 587-1788, (301) 587-1789 (TDD). http://www.nad.org.

Other

Cochlear Implant Recipients may be at Greater Risk forMeningitis. FDA Public Health Web Notification. October 17, 2002 [cited February 23, 2003]. http://www.fda.gov/cdrh/safety/cochlear.html.

— Carol A. Turkington Michelle L. Johnson

 

Definition

A cochlear implant is a surgical treatment for hearing loss that works like an artificial human cochlea in the inner ear, helping to send sound from the ear to the brain. It is different from a hearing aid, which simply amplifies sound.

Purpose

A cochlear implant bypasses damaged hair cells in the child's cochlea and helps establish some degree of hearing by stimulating the hearing (auditory) nerve directly.

Description

Hearing loss is caused by a number of different problems that occur either in the auditory nerve or in parts of the middle or inner ear. The most common type of deafness is caused by damaged hair cells in the cochlea. The cochlea is a fluid-filled canal in the inner ear that is shaped like a snail shell. Inside are thousands of tiny hairs called cilia. As sound vibrates the fluid in the cochlea, the cilia move. This movement stimulates the auditory nerve and sends messages about sound to the brain. When these hair cells stop functioning, the auditory nerve is not stimulated, and the child cannot hear. Hair cells can be destroyed by many things, including infection, trauma, loud noise, aging, and birth defects.

The first piece of a cochlear implant is the microphone. It is usually worn behind the ear, and it picks up sound and sends it along a wire to a speech processor. The speech processor is usually worn in a small shoulder pouch, pocket, or on a belt. The processor boosts the sound, filters out background noise, and turns the sound into digital signals. Then it sends these digital signals to a transmitter worn behind the ear. A magnet holds the transmitter in place through its attraction to the receiver-stimulator, a part of the device that is surgically attached beneath the skin in the skull. The receiver picks up digital information forwarded by the transmitter and converts it into electrical impulses. These electrical impulses flow through electrodes contained in a narrow, flexible tube that has been threaded into the cochlea during surgery and stimulate the auditory nerve. The auditory nerve carries the electrical impulses to the brain, which interprets them as sound.

Despite the benefits that the implant appears to offer, some hearing specialists and members of the deaf community still believe that the benefits may not outweigh the risks and limitations of the device. Because the device must be surgically implanted, it carries some surgical risk. Also, it is impossible to be certain how well any individual child will respond to the implant. After getting an implant, some people say they feel alienated from the deaf community, while at the same time not feeling fully a part of the hearing world.

The sounds heard through an implant are different from those sounds heard normally, and have been described as artificial or "robot-like." This is because the implant's limited number of electrodes cannot hope to match the complexity of a human's 15,000 hair cells. Cochlear implants are, however, becoming more advanced and providing even better sound resolution.

Surgical Procedure

During the procedure, the surgeon makes an incision behind the ear and opens the mastoid bone (the ridge on the skull behind the ear) leading into the middle ear. The surgeon then places the receiver-stimulator into a well made in the bone and gently threads the electrodes into the cochlea. This operation takes between an hour-and-a-half and five hours. It is performed using general anesthesia.

Precautions

Because the implants are controversial, very expensive, and have uncertain results, the United States Food and Drug Administration (FDA) has limited the implants to people for whom the following is true:

  • individuals who get no significant benefit from hearing aids
  • individuals who are at least 12 months old
  • individuals with severe to profound hearing loss

Preparation

Before a child gets an implant, specialists at an implant clinic conduct a careful evaluation, including extensive hearing tests to determine how well the child can hear.

First, candidates undergo a trial with a powerful hearing aid. If the hearing aid cannot improve hearing enough, a physician then performs a physical examination and orders a scan of the inner ear, because some patients with a scarred cochlea are not good candidates for cochlear implants. A doctor may also order a psychological exam to better understand the person's expectations. Patients and their families need to be highly motivated and have a realistic understanding of what an implant can and cannot do.

Aftercare

The child may remain in the hospital for a day or two after the surgery, although with improving technology and techniques some children may go home the same day. After about a month, the surgical wounds will have healed, and the child returns to the implant clinic to be fitted with the external parts of the device (the speech processor, microphone, and transmitter). A clinician tunes the speech processor and sets levels of stimulation for each electrode from soft to loud.

The child is then trained in how to interpret the sounds heard through the device. The length of the training varies from days to years, depending on how well the child can interpret the sounds heard. With the new approval for using cochlear implants in children as young as 12 months of age, the toddler may not be trained specifically to interpret the sounds in the same way an older child would. The specific therapy that is recommended is highly dependent on the age of the child.

Risks

As with all operations, there are a few risks of surgery. These include the following:

  • dizziness
  • facial paralysis (which is rare and usually temporary)
  • infection at the incision site

Scientists are not sure about the long-term effects of electrical stimulation on the nervous system. It is also possible that the implant's internal components may be damaged by a blow to the head. This may cause the device to stop working. In general the failure rate of the implants is only 1 percent after one year.

Parental Concerns

There is increasing debate about the use of cochlear implants in infants. This is considered by some to be desirable because, if the implantation is done before a child has begun to significantly acquire language, there is some evidence that the child may be able to develop at a pace similar to hearing children of the same age. Making a decision about whether or not a child, especially a very young one, should have a cochlear implant can be very difficult. The child's doctor may be able to provide parents with resources or put them in contact with other parents who have had to make the same decision whom they can consult.

See also Hearing impairment.

Resources

Books

Christiansen, John B., and Irene W. Leigh. Cochlear Implants in Children: Ethics and Choices. Washington DC: Gallaudet University Press, 2002.

Chute, Patrician M., and Mary Ellen Nevins. The Parents' Guide to Cochlear Implants. Washington DC: Gallaudet University Press. 2002.

Periodicals

Barker, Brittan A., and Bruce J. Tomblin. "Bimodal Speech Perception in Infant Hearing Aid and Cochlear Implant Users." Archives of Otolaryngology—Head & Neck Surgery 130 (May 2004): 582–87.

Chin, Steven B. "Children's Consonant Inventories after Extended Cochlear Implant Use." Journal of Speech, Language, and Hearing Research 46 (August 2003): 849–63.

Conor, Carol McDonald, and Teresa A. Zwolan. "Examining Multiple Sources of Influence on the Reading Comprehension Skills of Children Who Use Cochlear Implants." Journal of Speech, Language, and Hearing Research 47 (June 2004): 509–27.

Organizations

American Society for Deaf Children. PO Box 3355 Gettysburg, PA 17325. Web site: www.deafchildren.org.

[Article by: Tish Davidson, A.M. Carol A. Turkington]



 
Wikipedia: cochlear implant
Illustration of the internal parts of a cochlear implant.
Enlarge
Illustration of the internal parts of a cochlear implant.

A cochlear implant (CI) is a surgically implanted electronic device that provides a sense of sound to a person who is profoundly deaf or severely hard of hearing. The cochlear implant is often referred to as a bionic ear. Unlike hearing aids, the cochlear implant does not amplify sound, but works by directly stimulating any functioning auditory nerves inside the cochlea with electrical impulses. External components of the cochlear implant include a microphone, speech processor and transmitter.

Under the appropriate conditions, an implant can give a deaf person a useful auditory understanding of the environment and/or hearing and help them to understand speech, although post-implantation therapy is usually required. According to researchers at the University of Michigan [1], approximately 100,000 people worldwide have received cochlear implants; roughly half are children and half are adults. The vast majority are in developed countries due to the prohibitive cost of the device, surgery and post-implantation therapy — Mexico had performed only 55 cochlear implant operations by the year 2000 (Berruecos 2000). China will be having 15,000 cochlear implant surgeries on children, which are being paid for by a Taiwanese philanthropist. The concern is that the follow-up services in China are not adequate to meet the needs of cochlear implanted children [1]. A small percentage of those now have bilateral implants, or one on each cochlea. Bilateral cochlear implants are a growing trend globally, Cochlear Americas reported that 15% of their 2006 sales in the United States were for bilateral implants. [2]


Individuals who have acquired deafblindness (loss of hearing and vision combined) may find cochlear implants a radical improvement in their daily life. It may provide them with more information for safety, communication, balance, orientation and mobility and promote interaction within their environment and with other people, reducing isolation. Having more auditory information that they may be familiar with may provide them independent gathering of information to become more independent.

The introduction of cochlear implants has seen the renewal of a century-old debate about models of deafness that often has the hearing parents of deaf children on one side and the deaf community on the other. University of Pittsburgh science affiliation, led by prominent bio-molecular audiologist Michael Kraemer, has crafted the basic audiological structure for the cohesion to operate properly. On the one hand, modern medical ethics law dictates that the decision of whether to get a cochlear implant is up to the patient or the legal guardian of the patient. Therefore, political debate about whether deafness is a disability or not is irrelevant to the current medical profession. On the other hand, whether society treats deafness as a disability has direct bearing on government policy. Many governments in the world have disability legislation which includes people who are deaf. Some developed countries provide cochlear implantation as a part of state healthcare.[3] The debate is also economic. Many state-funded medical interventions for a disability (such as free genetic screening for Down Syndrome) are justified on the ground that, in the long run, they will prove cheaper for the state. Sweden is the only country that has legislation that when a deaf child is born to a hearing parent, they are, by law, consulted by the deaf community as well as the medical community so they can make an informed decision.

History

The discovery that electrical stimulation to the auditory system can create a perception of sound occurred around 1790, when Alessandro Volta (the developer of the electric battery) placed metal rods in his own ears and connected them to a 50-volt circuit, experiencing a jolt and hearing a noise "like a thick boiling soup". Other experiments occurred sporadically, until electrical (sound amplifying) hearing aids began to be developed in earnest in the 20th century.

The first direct stimulation of an acoustic nerve with an electrode was performed in the 1950s by the French-Algerian surgeons André Djourno and Charles Eyriès. They placed wires on nerves exposed during an operation, and reported that the patient heard sounds like "a roulette wheel" and "a cricket" when a current was applied.

In 1961, American doctor William F. House of House Ear Institute [4] and House ear clinic[5] had Djourno's paper translated and had devices made which he implanted into three patients. In 1969, with the help of Jack Urban, House created the first wearable cochlear implant. House's technology used a single electrode and was designed to aid lip-reading. Throughout the 1970s, University Of Melbourne researcher Graeme Clark, initially inspired to develop an artificial hearing device through his deaf father[6], developed implants which stimulated the cochlea at multiple points, and on the 1st of August, 1978, Melbourne resident Rod Saunders became the first person in the world to receive a multi-channel cochlear implant.

In December 1984, the Australian cochlear implant was approved by the United States Food and Drug Administration to be implanted into adults in the United States. In 1990 the FDA lowered the approved age for implantation to 2 years, then 18 months in 1998, and finally 12 months in 2002, although off label use has occurred in babies as young as 6 months in the United States and 4 months internationally.

Throughout the 1990s, the large external components which had been worn strapped to the body grew smaller and smaller thanks to developments in miniature electronics. By 2006, most school-age children and adults used a small behind-the-ear (BTE) speech processor about the size of a power hearing aid. Younger children have small ears and might mishandle behind-the-ear speech processors, therefore, they often wear the speech processor on their hip in a pack or small harness, or wear the BTE's pinned to their collar, barrette or elsewhere.

Since hearing in two ears allows people to localize sounds and to hear better in noisy environments, bilateral (both ear) implants are currently being investigated and utilized. Users generally report better hearing with two implants, and tests show that bilateral implant users are better at localizing sounds and hearing in noise. Nearly 3000 people worldwide are bilateral cochlear implant users, including 1600 children. As of 2006, the world's youngest recipient of a bilateral implant was just over 5 months old (163 days) in Germany (2004).

Parts of the cochlear implant

The implant is surgically placed under the skin behind the ear. The basic parts of the device include:

External:
  • a microphone which picks up sound from the environment
  • a speech processor which selectively filters sound to prioritise audible speech and sends the electrical sound signals through a thin cable to the transmitter,
  • a transmitter, which is a magnetic pad placed behind the external ear, and transmits the processed sound signals to the internal device by electromagnetic induction,
Internal:
  • a receiver and stimulator secured in bone beneath the skin, which converts the signals into electric impulses and sends them through an internal cable to electrodes,
  • an array of up to 24 electrodes wound through the cochlea, which send the impulses directly into the brain.

Candidates

There are a number of factors that determine the degree of success to expect from the operation and the device itself. Cochlear implant centers determine implant candidacy on an individual basis and take into account a person's hearing history, cause of hearing loss, amount of residual hearing, speech recognition ability, health status, and family commitment to aural habilitation/rehabilitation.

A prime candidate is described as:

  • having severe to profound sensorineural hearing impairment in both ears
  • having a functioning auditory nerve
  • having lived a short amount of time without hearing (approximately 70+ decibel loss, on average)
  • having good speech, language, and communication skills, or in the case of infants and young children, having a family willing to work toward speech and language skills with therapy
  • not benefitting enough from other kinds of hearing aids
  • having no medical reason to avoid surgery
  • living in or desiring to live in the "hearing world"
  • having realistic expectations about results
  • having the support of family and friends
  • having appropriate services set up for post-cochlear implant aural rehabilitation (through a speech language pathologist, deaf educator, or auditory verbal therapist).

Type of hearing impairment

People with mild or moderate sensorineural hearing loss are generally not candidates for cochlear implantation. After the implant is put into place, sound no longer travels via the ear canal and middle ear but will be picked up by a microphone and sent through the device's speech processor to the implant's electrodes inside the cochlea. Thus, most candidates have been diagnosed with profound sensorineural hearing loss.

The presence of auditory nerve fibres is essential to the functioning of the device: if these are damaged to such an extent that they cannot receive electrical stimuli, the implant will not work. A small number of individuals with severe auditory neuropathy may also benefit from cochlear implants.

Age of recipient

Post-lingually deaf adults and pre-lingually deaf children form two distinct groups of potential users of cochlear implants with different needs and outcomes. Those who have lost their hearing as adults were the first group to find cochlear implants useful, in regaining some comprehension of speech and other sounds. If an individual has been deaf for a long period of time, the brain may begin using the area of the brain normally used for hearing for other functions. If such a person receives a cochlear implant, the sounds can be very disorienting, and the brain often will struggle to readapt to sound.

The risk of surgery in the older patient must be weighed against the improvement in quality of life. As the devices improve, particularly the sound processor hardware and software, the benefit is often judged to be worth the surgical risk, particularly for the newly deaf elderly patient. [7]

The other group of customers are parents of children born deaf who want to ensure that their children grow up with good spoken language skills. Research shows that congenitally deaf children who receive cochlear implants at a young age (less than 2 years) have better success with them than congenitally deaf children who first receive the implants at a later age, though the critical period for utilizing auditory information does not close completely until adolescence.

Number of users

It has been estimated in 2002 that around 10,000 children in the US and an additional 49,000 people worldwide have received Cochlear implants.[2]


The operation, post-implantation therapy and ongoing effects

Cochlear implant as worn by user
Enlarge
Cochlear implant as worn by user

The device is surgically implanted under a general anaesthetic, and the operation usually takes from 1½ to 5 hours. First a small area of the scalp directly behind the ear is shaved and cleaned. Then a small incision is made in the skin just behind the ear and the surgeon drills into the mastoid bone and the inner ear where the electrode array is inserted into the cochlea. The patient normally goes home the same day as the surgery, although some cochlear implant recipients stay in the hospital for 1 to 2 days. It is considered outpatient surgery. As with every medical procedure, the surgery involves a certain amount of risk; in this case, the risks include skin infection, onset of tinnitus, damage to the vestibular system, and damage to facial nerves that can cause muscle weakness, or, in worst cases, disfiguring paralysis. There is also the risk of device failure, usually where the incision does not heal properly. This occurs in 2% of cases and the device must be removed. The operation also may destroy any residual hearing the patient may have; as a result, some doctors advise single-ear implantation, saving the other ear in case a biological treatment becomes available in future.

After 1-4 weeks of healing (the wait is usually longer for children than adults), the implant is turned on or activated. Results are typically not immediate, and post-implantation therapy is required as well as time for the brain to adapt to hearing new sounds. In the case of congenitally deaf children, audiological training and speech therapy typically continue for years, though infants can become age appropriate in a matter of months. The participation of the child's family in working on spoken language development is considered to be even more important than therapy. The family can aid development by participating actively in the child's therapy, making hearing and listening interesting, talking about objects and actions, and encouraging the child to make sounds and form words.

In 2003, the CDC and FDA announced that children with cochlear implants are at a slightly increased risk of bacterial meningitis (Reefhuis 2003). Though this risk is small, it is still 30 times higher than children in the general population, without proper immunizations. Many users, audiologists, and surgeons also report that when there is an ear infection causing fluid in the middle ear, it can affect the cochlear implant, leading to temporarily reduced hearing.

The implant has a few effects unrelated to hearing. Manufacturers have cautioned against scuba diving due to the pressures involved, but the depths found in normal recreational diving appear to be safe. The external components must be turned off and removed prior to swimming or showering. Some brands of cochlear implant are unsafe in areas with strong magnetic fields, and thus cannot be used with certain diagnostic tests such as magnetic resonance imaging (MRI), but some are now FDA approved for use with certain strengths of MRI machine. Large amounts of static electricity can cause the device's memory to reset. For this reason, children with cochlear implants are also advised to avoid plastic playground slides. [8] The electronic stimulation the implant creates appears to have a positive effect on the nerve tissue that surrounds it.[citation needed]

Cost

In the United States, medical costs run from USD$45,000 to $105,000; this includes evaluation, the surgery itself, hardware (device), hospitalization and rehabilitation. Some or all of this may be covered by health insurance. In the United Kingdom, the NHS covers cochlear implants in full.

Efficiency

A cochlear implant will not cure deafness or hearing impairment, but is a prosthetic substitute for hearing. Some recipients find them very effective, others somewhat effective and some feel overall worse off with the implant than without. [9] For people already functional in spoken language who lose their hearing, cochlear implants can be a great help in restoring functional comprehension of speech, especially if they have only lost their hearing for a short time.

British Member of Parliament Jack Ashley received a cochlear implant in 1994 at age 70 after 25 years of deafness, and reported that he has no trouble speaking to people he knows one on one, even on the telephone, although he might have difficulty with a new voice or with a busy conversation, and still had to rely to some extent on lipreading. He described the robotic sound of human voices perceived through the cochlear implant as "a croaking dalek with laryngitis". Even modern cochlear implants have at most 24 electrodes to replace the 16,000 delicate hair cells that are used for normal hearing. However, the sound quality delivered by a cochlear implant is often good enough that many users do not have to rely on lipreading. Rush Limbaugh, U.S. talk radio show host, says that everything sounds normal except that he cannot pick out the melody of new music that he had not heard prior to becoming deaf.

Adults who have grown up deaf can find the implants ineffective or irritating. This relates to the specific pathology of deafness and the time frame. Adults who are born with normal hearing and who have had normal hearing for their early years and who have then progressively lost their hearing tend to have better outcomes than adults who were born deaf. This is due to the neural patterns laid down in the early years of life - which are crucially important to speech perception. Cochlear implants cannot overcome such a problem. Some who were orally educated and used amplifying hearing aids have been more successful with cochlear implants, as the perception of sound was maintained through use of the hearing aid.

Many individuals who use sign language believe they have no use for sound, with the obvious exception of the detection of emergency situations (onrushing vehicles, law enforcement officials calling to them or attackers) located outside the range of vision. Individuals who are deaf use sign language and an interpreter to communicate with those who use spoken languages, in the same way that an individual who only speaks English but wants to meet with an individual who only speaks French, would utilize an interpreter.

For small children, amazing results have been achieved with the use of cochlear implants[3]. Almost all children hear quite well with a cochlear implant, save for a rare few. Those children without a working auditory nerve may be helped with a cochlear implant, although the results they experience may not be as spectacular. Patients without a viable auditory nerve are usually identified during the candidacy process. Fewer than 1% of deaf individuals have a missing or damaged auditory nerve, which today can be treated with an auditory brainstem implant. Recent research has suggested that children and adults can benefit from bilateral cochlear implants in order to aid in sound localization and speech understanding. (See Offeciers et al. 2005)

Risks and disadvantages

The FDA reports that cochlear implant recipients may be at higher risk for meningitis.[10] A study of 4,265 American children who received implants between 1997 and 2002 concluded that recipient children had a risk of pneumococcal meningitis more than 30 times greater than that for children in the general population.[11] A later, UK-based, study found that while the incidence of meningitis in implanted adults was significantly higher than the general population, the incidence in children was no different than the general population.[12]

There are strict protocols in choosing candidates to avoid risks and disadvantages. A battery of tests are performed to make the decision of candidacy easier. For example, some patients suffer from deafness medial to the cochlea - typically acoustic neuromas. Implantation into the cochlea has a low success rate with these people as the artificial signal doesn't have a healthy nerve to travel along.

With careful selection of candidates, the risks of implantation are minimized.

Ethical issues

Discussions within the deaf community continue to fuel controversy and emotional personal debates about health, rights of the individual citizen, language, ethics, deaf culture, and the death of deaf culture. Part of the controversy concerns also the basic right for an individual to choose a language versus an individual as a young child having a mode of communication and language chosen for them. In the past, many adults whose first language is sign language endured policies created by medical and educational governing bodies that enforced the use of spoken language and use of hearing aids on them. One argument made by those in the deaf community opposed to cochlear implants is that implantation of CI's in young children is just another form of abuse. In the past, individuals who were deaf have advocated change successfully to improve human rights for individuals and continue to work to advocate for change, to help children who are born with loss of hearing.

Cochlear implants for congenitally deaf children are often considered to be most effective when implanted at a young age, during the critical period in which the brain is still learning to interpret sound; hence they are implanted before the recipients can decide for themselves. Critics question the ethics of such invasive elective surgery on otherwise healthy children. They point out that manufacturers and specialists have exaggerated the efficacy and downplayed the risks of a procedure that they stand to gain from. On the other hand, Andrew Solomon of the New York Times states that "Much National Association of the Deaf propaganda about the danger of implants is alarmist; some of it is positively inaccurate."[4]

Much of the strongest objection to cochlear implants has come from the deaf community, which consists largely of pre-lingually deaf people whose first language is a signed language. Regardless of the fact that to be deaf is to lack the ability to hear, many individuals who are deaf and the deaf community do not share the view of deafness held by the hearing parents of deaf children, which obviously regards deafness as a disability to be "fixed." Individuals who are deaf celebrate their diverse culture (see deaf culture). On the other hand, many people feel that refusing to implant deaf children is unethical, comparable to refusal to treat any other handicap or disease that can be effectively alleviated. Many individuals who can hear, or who have experienced the wonder of hearing before going deaf, are not comfortable with the thought of a child that lacks the sense most commonly associated with human language. Individuals who are deaf may feel that implants are just another form of mental and physical abuse in the long history of punishments, abuse and pain they have had to endure.

The conflict over these opposing models of deafness has raged since the 18th century, and cochlear implants are the latest in a history of medical interventions promising to turn a deaf child into a hearing child — or, more accurately, into a child with a mild or moderate hearing impairment.

Critics argue that the cochlear implant and the subsequent therapy often become the focus of the child's identity, at the expense of a deaf identity and ease of communication in sign language. Measuring the child's success by their success in hearing and speech will lead to a poor self-image as "disabled" (because the implants do not produce normal hearing) rather than having the healthy self-concept of a proud deaf person.[5]

Some writers have noted that children with cochlear implants are more likely to be educated orally and without access to sign language (Spencer et al 2003). Children with implants are also often isolated from other deaf children and from sign language (Spencer 2003), and instead are 'married' to a team of hearing experts who will monitor his cochlear implant and adjust the speech processor, at great expense. Children do not always receive support in the educational system to support their needs as they may require special education environments and EA's Educational Assistants. According to Johnston (Johnston 2004), cochlear implants have been one of the technological and social factors implicated in the decline of sign languages in the developed world. Some of the more extreme responses from deaf activists have labelled the widespread implantation of children as "cultural genocide". As cochlear implants began to be implanted into deaf children in the mid to late 1980s, the deaf community responded with protests in the US, UK, Germany, Finland, France and Australia.

Opposition continues today but is softening. As the trend for cochlear implants in children grows, deaf-community advocates have tried to counter the "either or" formulation of oralism vs manualism with a "both and" approach; some schools now are successfully integrating cochlear implants with sign language in their educational programs. However, some opponents of sign language education argue that the most successfully implanted children are those who are encouraged to listen and speak rather than overemphasize their visual sense. Significantly, deaf individuals have a high rate of illiteracy due to the phonetic nature of the western writing systems; it is thought that cultivating the auditory senses will help a hearing impaired child to avoid this problem. However, others (mainly deaf people who have been through education in decades past) feel that the high levels of relative illiteracy is mainly due to profoundly deaf children being taught orally, despite being sign language users and not being able to fully understand speech. Oral education in the past, though, was vastly different from the approaches today, which have the benefit of hearing with cochlear implants. Previous generations relied heavily on lipreading; today's implanted person can often hear well with no lipreading whatsoever.

A recent study[6] about attitudes of young, implanted people shows, that their feelings about the implantation are overhelmingly positive; although they are aware of the negative effects, too. None of the teenagers participating in the study criticised their parents for making the decision. They developed a positive identity, felt that they belonged to both the hearing and deaf worlds; although only some of them use both spoken and sign language.

Functionality

The implant works by using the tonotopic organization of the basilar membrane of the inner ear. "Tonotopic organization", also referred to as a "frequency-to-place" mapping, is the way the ear sorts out different frequencies so that our brain can process that information. In a normal ear, sound vibrations in the air lead to resonant vibrations of the basilar membrane inside the cochlea. High-frequency sounds (i.e. high pitched sounds) do not pass very far along the membrane, but low frequency sounds pass farther in. The movement of hair cells, located all along the basilar membrane, creates an electrical disturbance that can be picked up by the surrounding nerve cells. The brain is able to interpret the nerve activity to determine which area of the basilar membrane is resonating, and therefore what sound frequency is being heard.

In individuals with sensorineural hearing loss, hair cells are often fewer in number and damaged. Hair cell loss or absence may be caused by a genetic mutation or an illness such as meningitis. Hair cells may also be destroyed chemically by an ototoxic medication, or simply damaged over time by excessively loud noises. The cochlear implant bypasses the hair cells and stimulates the cochlear nerves directly using electrical impulses. This allows the brain to interpret the frequency of sound as it would if the hair cells of the basilar membrane were functioning properly (see above).

Processing

Sound received by the microphone must next be processed to determine how the electrodes should be activated. The simplest way of processing would be to divide the acoustic signal by the number of electrodes in the device and apply the resulting voltage to the appropriate electrode. More sophisticated processing algorithms are used in practice because applying voltage to each of the electrodes simultaneously could cause non-charge-balanced currents to flow between the electrodes. This could stimulate the nerves in undesirable ways and lead to both tissue and electrode damage by essentially electrocuting individual nerve cells.

Fourier strategies use bandpass filters to divide the signal into different frequency bands. The algorithm chooses a number of the strongest outputs from the filters, the exact number depending on the number of implanted electrodes and other factors. These strategies emphasize transmission of the temporal aspects of speech.

Feature extraction strategies use features which are common to all vowels. Each vowel has a fundamental frequency (the lowest frequency peak) and formants (peaks with higher frequencies). The pattern of the fundamental and formant frequencies is specific for different vowel sounds. These algorithms try to recognize the vowel and then emphasize its features. These strategies emphasize the transmission of spectral aspects of speech. Feature extraction strategies are no longer widely used.

Transmitter

This is used to transmit the processed sound information over a radio frequency link to the internal portion of the device. Radio frequency is used so that no physical connection is needed, which reduces the chance of infection. The transmitter attaches to the receiver using a magnet that holds through the skin.

Receiver

This component receives directions from the speech processor by way of radio waves sent from the transmitter. (The receiver also receives its power through the transmission.) The receiver is also a sophisticated computer that translates the processed sound information and controls the electrical current sent to the electrodes in the cochlea. It is embedded in the skull behind the ear.

Electrode array

The electrode array is made from a type of silicone rubber, while the electrodes are platinum or a similarly highly conductive material. It is connected to the internal receiver on one end and inserted into the cochlea deeper in the skull. (The cochlea winds its way around the auditory nerve, which is tonotopically organized just as the basilar membrane is). When an electrical current is routed to an intracochlear electrode, an electrical field is generated and auditory nerve fibers are stimulated.

In the devices manufactured by Cochlear Ltd, two electrodes sit outside the cochlea and acting as grounds-- one is a ball electrode that sits beneath the skin, while the other is a plate on the device. This equates to 24 electrodes in the Cochlear-brand 'nucleus' device, 22 array electrodes within the cochlea and 2 extra-cochlear electrodes.

Speech Processors

Speech Processors are the component of the cochlear implant that transforms the sounds picked up by the microphone into electronic signals capable of being transmitted to the internal receiver. The coding strategies programmed by the user's audiologist are stored in the processor, where it codes the sound accordingly. The signal produced by the speech processor is sent through the coil to the internal receiver, where it is picked up by radio signal and sent along the electrode array in the cochlea.

There are primarily two forms of speech processors available. The most common kind is called the "behind-the-ear" processor, or BTE. It is a small processor that is kept worn on the ear, typically together with the microphone. This is the kind of processor used by most adults and older children.

The other form is called a body-worn-processor. This is the kind used typically by younger children, whose ears are too small to properly fit the bulky BTE processor (though it is gradually being phased out, with baby and child friendly BTEs on the market). The body worn processor is kept on the user's body, and a long wire extends up to the microphone earpiece to connect it with the processor. Users of the body worn processor have to find some creative way where to place the body worn processor. Some mothers place the processor on the child's back in a pocket sewn onto a T-shirt or onesie, others use a harness that clips across the child's chest. In July 2007, Cochlear Corp., the maker of the Nucleus brand of cochlear implants, announced that they will be making an accessory called "Babyworn", that will allows the BTE processor to be worn with a small battery pack that will clip onto the babies clothing[7]. This will possibly diminish demand for the Bodyworn style processor. Advanced Bionics will likely come out with a similar accessory for their processor in the near future. Med-el has had a baby-friendly BTE which pins on the collar on the U.S. market since the fall of 2001; 70% of their market is to children.

Programming the speech processor

The cochlear implant must be programmed individually for each user. The programming is performed by an audiologist trained to work with cochlear implants. The audiologist sets the minimum and maximum current level outputs for each electrode in the array based on the user's reports of loudness. The audiologist also selects the appropriate speech processing strategy and program parameters for the user.

Manufacturers

Currently (as of 2007), the four cochlear implant devices are manufactured by Cochlear Limited, Australia, MED-EL, Austria, Advanced Bionics, US, and Neurelec, France. Each manufacturer has adapted some of the successful innovations of the other companies to their own devices. There is no clear-cut consensus that any one of these implants is superior to the others. Users of all four devices display a wide range of performance after implantation.

Since the devices have a similar range of outcomes, other criteria are often considered when choosing a cochlear implant: usability of external components, cosmetic factors, battery life, reliability of the internal and external components, MRI compatibility, mapping strategies, customer service from the manufacturer, the familiarity of the user's surgeon and audiologist with the particular device, and anatomical concerns.

Cochlear Americas, the Americas subsidiary for the largest cochlear implant manufacturer, Cochlear Limited, acknowledged to shareholders in March 2004 that it is under investigation by the U.S. Department of Justice for offering inducements to physicians in exchange for prescribing devices made by Cochlear. See Australian Stock Exchange Release. In its Annual Report of September 2007 Cochlear indicated that DOJ had passed the investigation to the Office of the Inspector General for administrative processing. Cochlear's Australian Stock Exchange filings in August 2007 also reported a record profit of A$100 million (or just over US$85 million) and a 70 percent market share.

Cochlear implant in popular culture

In 2000, an Academy Award nominated documentary film Sound and Fury depicted the cultural divide between the deaf community and children with cochlear implants. The Artinian family themselves are a "microcosm" of the deaf culture war and two children – Peter (11 months old) and Heather (7 yrs old) – are caught in the middle. Many of the family members who opposed cochlear implants later went on to receive implants or allow their children to be implanted, and have become strong advocates for cochlear implants.

Famous recipients of cochlear implants include British MP Jack Ashley, conservative U.S. talk-show host Rush Limbaugh, British designer and typographer Tony Malone, and Heather Whitestone, Miss America 1995. Sigrid Cerf, wife of the creator of TCP/IP and Chief Internet Evangelist Vint Cerf, has two cochlear implants. Vint Cerf has a hearing impairment himself, and has spoken in support of the Hear and Say Centre, a cochlear implant and speech training organisation based in Brisbane, Australia.

On the television show ER, Reese Benton, the son of Dr. Peter Benton, is born deaf and his father briefly considers giving his son a cochlear implant.

On the television show Scrubs, the son of Mr. Francis is a child born deaf that ends up receiving a cochlear implant.

On the long running soap opera The Young and The Restless, Neil and Drusilla Winters adoptive son Devon lost his hearing due to meningitis and got a Cochlear Implant so he could hear again.

On the long running soap opera "Guiding Light", former actress Amy Ecklund received the cochlear implant in 1999. It was written into the show weeks later.

A Cochlear Implant is present in the video game series Splinter Cell as a means of communication without obvious microphones and the risk of being overheard and is used by the protagonist Sam Fisher.

On the television show, "What About Brian", the daughter of Dave and Deena, Carrie, gets a cochlear implant.

The Michael Moore film Sicko documents one families' process in fighting against CIGNA to receive a sequential bilateral cochlear implant for their daughter. That child was a client of the Let Them Hear Foundation Insurance Advocacy Program. After several other appeals and an investigation opened by the Florida Attorney General, CIGNA finally changed their policy to include bilateral cochlear implants as a standard benefit in all traditionally insured plans in May of 2007.

See also

References

  1. ^ Cochlear Corp. News
  2. ^ van der Heijden, Dennis (2006-03-01). What are Cochlear Implants?. Axistive. Retrieved on 2007-03-01.
  3. ^ http://www.medicalnewstoday.com/articles/46327.php
  4. ^ Defiantly Deaf.
  5. ^ Cochlear Implants.
  6. ^ Wheeler, A., Archbold, S., Gregory, S.: "Cochlear implants: young people's view", The National Deaf Children's Society & The Ear Foundation, 2007
  7. ^ http://hearingpocket.wordpress.com/2007/07/27/babyworn-is-here/
  • Berruecos, Pedro. (2000). Cochlear implants: An international perspective - Latin American countries and Spain. Audiology. Hamilton: Jul/Aug 2000. Vol. 39, 4:221-225
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  • Djourno A, Eyriès C. (1957). 'Prothèse auditive par excitation électrique à distance du nerf sensoriel à l'aide d'un bobinage inclus à demeure.' In: La Presse Médicale 65 no.63. 1957.
  • Djourno A, Eyriès C, (1957) 'Vallencien B. De l'excitation électrique du nerf cochléaire chez l'homme, par induction à distance, à l'aide d'un micro-bobinage inclus à demeure.' CR de la société.de biologie. 423-4. March 9, 1957.
  • Eisen MD (2003), 'Djourno, Eyries, and the first implanted electrical neural stimulator to restore hearing.' in: Otology and Neurotology. 2003 May;24(3):500-6.
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  • Lane, H. and Bahan, B. (1998). Effects of Cochlear Implantation in Young Children: A Review and a Reply from a DEAF-WORLD Perspective. Otolaryngology: Head and Neck Surgery 119:297-308.
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  • Lane, Harlan (1994), The Cochlear Implant Controversy. World Federation of the Deaf News 2 (3):22-28.
  • Litovsky, Ruth Y., et al. (2006). "Bilateral Cochlear Implants in Children: Localization Acuity Measured with Minimum Audible Angle." Ear & Hearing, 2006; 27; 43-59.
  • Miyamoto, R.T.,K.I.Kirk, S.L.Todd, A.M.Robbins, and M.J.Osberger. (1995). Speech Perception Skills of Children with Multichannel Cochlear Implants or Hearing Aids. Annals of Otology, Rhinology and Laryngology 105 (Suppl.):334-337
  • Officiers, P.E., et. a. (2005). "International Consensus on bilateral cochlear implants and bimodal stimulation." Acta Oto-Laryngologica, 2005; 125; 918-919.
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