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Cochlear implant

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. Cochlear implants are often referred to as a bionic ear.

Cochlear implants may help provide hearing in patients that are deaf due to damage to sensory hair cells in their cochlea. In those patients, they can often enable sufficient hearing to allow better understanding of speech. The quality of sound is different from natural hearing, with less sound information being received and processed by the brain. However, many patients are able to hear and understand speech and environmental sounds. Newer devices and processing strategies allow recipients to hear better in noise, enjoy music, and even use their implant processors while swimming.

As of December 2010, approximately 219,000 people worldwide have received cochlear implants; in the U.S., roughly 42,600 adults and 28,400 children are recipients.^[1] The vast majority are in developed countries due to the high cost of the device, surgery and post-implantation therapy. A small but growing segment of recipients have bilateral implants (one implant in each cochlea).^[2]

History

This section needs additional citations for verification. (March 2012)

The discovery that electrical stimulation in 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.

The first attempt to develop a clinical CI was in 1957 by Djourno and Eyriès. A recipient was implanted with a single channel device. Unprocessed sounds were transmitted via a pair of solenoid-like coils. The link was therefore transcutaneous; it did not require a break in the skin after implantation. This device failed after a short time and another device was implanted. After this second device failed, Eyriès refused to implant a third device. He urged Djourno to collaborate with an industry partner to build a more reliable device. Djourno refused because he believed that academia should not be tainted by commerce. Djourno found another surgeon, Roger Maspétiol, who implanted a second patient in 1958. Although these recipients were unable to understand speech with the device alone, it helped with lipreading by providing the rhythm of the speech.^{[citation needed]}

In 1961 Dr William House (an otologist), John Doyle (a neurosurgeon) and James Doyle (an electrical engineer) commenced work on a single-channel device in Los Angeles. In one case a five-wire electrode was used but the same signal was applied to all contacts. House’s work continued in the 1970s in collaboration with engineer Jack Urban. Their implant was also a single-channel device but, in this case, the speech was modulated onto a carrier of 16 kHz. The device, manufactured by 3M, was ultimately implanted in some thousand or so recipients and paved the way for future clinical development of multichannel CIs.^[3] The House/3M unit was the first approved by the FDA for implantation in adults in 1984.

In 1964, Blair Simmons at Stanford University implanted some recipients with a six-channel device. This device used a percutaneous plug to enable the electrodes to be individually stimulated. Recipients could still not understand speech through the device but, importantly, it demonstrated that by stimulating in different areas of the cochlea, different pitch percepts could be produced.^[4]

In 1970, Robin Michelson, M.D., reported preliminary results of cochlear implantation in three deaf adults implanted with gold wire electrodes. Initially he teamed with Mel Bartz, an electrical engineer working with Storz, Inc. Michelson's report to the American Academy of Otolaryngology and Ophthalmology created a tempest. Orthodox auditory theory was in confusion at the time, and it was not thought possible for direct electrical stimulation of neural tissue to convey meaningful sound to the brain. Michelson conducted some work in San Francisco, in the Coleman Laboratory at the University of California, a foundation funded by the wealthy ENT department chairman at UCSF, Francis Sooy, MD. Michelson's implantation of humans before animal physiology experiments caused consternation among physiologists, audiologists, and many otologists. An otolaryngology resident, C. Robert Pettit, heard Michelson describe the results of his cochlear implantations at a department educational meeting. He ran to the Coleman Laboratory, where Michelson spent one half-day per week away from his Redwood City private ENT practice, and told the older surgeon of his dream since college of a multi-channel electrode resembling a hairbrush. Michelson said so many stimulus points were not necessary and that his patients were hearing "in stereo" with a two-channel electrode he had designed. Michelson and Pettit teamed to build the bipolar electrodes embedded in silastic which replaced the broken gold electrodes in Michelson's three patients. The reimplantation procedures were carried out in Redwood City Community Hospital, not at UC San Francisco, as were the original implants.

Soon, the UCSF department chairman recruited Michael Merzenich, a young PhD, to carry out his research interests in neurophysiology, mapping the inferior colliculus, and to investigate the potential of cochlear implantation. Merzenich was enormously skeptical of the cochlear implant project, but agreed to test cats Michelson and Pettit had implanted. Merzenich was skilled at constructing micro-electrode needles capable of penetrating single nerve cells without rupturing the cell membranes and spilling cell contents. He agreed to monitor electrical activity in inferior colliculus cells of cats stimulated by normal sound in one ear, and electrical input from a cochlear implant in the other ear, finding both auditory stimuli similar. Merzenich had constructed an advanced electronic bank of signal generating and monitoring equipment for use for in his mapping experiments and a carefully shielded soundproof booth for testing. Over the months of animal testing, Merzenich became convinced that the electrical signal from the cochlear implant was entering the brain and was "phase-locked." Understanding what humans heard with the cochlear implant was another matter.

New tests were devised for implanted patients. One was congenitally deaf and had never heard sound. Pettit employed a music professor to synthesize simple tunes and sounds in various sound envelopes, and new pitch and loudness-scaling tests were devised. When one of the reimplanted patients was tested by the team under carefully controlled laboratory conditions, in 1972, a version of "Where Have All the Flowers Gone?" played on a Moog Synthesizer was presented to the patient through the cochlear implant. The camera caught the patient humming the melody and tapping a pencil to the tempo of the tune. That sequence convinced the department chairman to support the cochlear implant project. When the film was shown to a meeting of otologists later in 1972, it convinced the scientific community that meaningful sound could be conveyed to the brain by electrical stimulation of the auditory nerve.^[5][6]

Cochlear implants that operate successfully, including those produced by all three major manufacturers (Cochlear Corporation, Advanced Bionics and Med-El), incorporate the same basic design. Likewise, all cochlear implants incorporate the same basic design to be capable of the ultimate goal of "detecting" or "demodulating" intelligence from the human voice when that intelligence is residing within an electronic signal. The successful cochlear implant must also be capable of converting the pattern of the detected intelligence into an appropriate electronic format for application to the acoustic (eighth cranial) nerve, which in turn further transmits the encoded pattern to the hearing center of the brain, where the information is interpreted as meaningful intelligence. That is why implants from all (three) major manufacturers work equally well in functionality, but are quite different in final design enhancements. Design of this basic conversion process was first described by Adam Kissiah, Jr., and was first exposed to the public when it was revealed to James O. Harrell, Esquire, Patent Counsel to NASA's John F. Kennedy Space Center, in July, 1974. Mr. Harrell also advised exposure to another person capable of understanding the concept. This was done on August 1, 1974. Subsequent Patent Office search and patent application for letters patent was completed in May 1977. Patent 4063048 was issued to Adam M. Kissiah, Jr. on December 13, 1977; Reissue 31031, which further improved design, was issued in September 1982.

Some cochlear implant designs and intra-cochlear implantations were made by others (see Cochlear Technology by Adam M. Kissiah, Jr.) prior to the mid-1970s, and were considered "successful" from a surgical and medical point of view. An equal number of proclamations and claims of being "firsts" in cochlear implantation were also made. Indeed, many important advances in cochlear implantation were accomplished during the 1960s and '70s. These earlier implants were capable of providing background sounds, and provided some aid to lip reading, and thus enabled patients to attain a most welcome sense of "attachment" to the world of sound. These earlier implants were incapable, however, of providing the ultimate level of comprehension of the intelligence of the spoken human voice enjoyed by the implant users of today. This fact can be supported by review of the many volumes of quarterly reports provided by many researchers under contract to the National Institutes of Health.

Greater understanding of voice intelligence was accomplished as the designs described in this first patent for the Cochlear Implant (4063048, December 13, 1977) were utilized in subsequent cochlear implants. Although Adam Kissiah was a full-time employee with NASA at the Kennedy Space Center, he participated as a consultant in an implantation program during the early 1980s through license agreement granted by Kissiah to Biostim, Inc., who in turn participated (also by contractual agreement) with Stanford University, Dr. Robert L. White and Dr. F Blair Simmons, principal investigators, during their program of cochlear implants (See Stanford University Cochlear Implant Program).

In 1976 a paper (received Feb 1975) was published by Pialoux, Chouard and McLeod that stated that, in the six months before the paper's submission, seven patients were implanted with an eight-channel device.^[7] Although it was reported that about 50% of ordinary words were understood without lipreading, this has not been supported by audiological data in the literature.

In 1972 the House 3M single-electrode implant was the first to be commercially marketed.^[8] However, it was Dr. Michelson's patents and ultimately device which are thought of as the first cochlear implants.^[9]

Parallel to the developments in California, in the 1970s there were two other groups working on the development of the cochlear implant in Vienna, Austria, and Melbourne, Australia. On December 16, 1977, professor Kurt Burian implanted a multichannel cochlear implant. The device was developed by the scientists Ingeborg and Erwin Hochmair, who founded MED-EL, producer of hearing implants, in 1989.^[10]

Professor Graeme Clark A.C., then Foundation Professor of the Department of Otolaryngology at the University of Melbourne in 1970, led the team that developed the Australian prototype bionic ear, which was implanted into the first patient, Rod Saunders, in 1978.

The prototype for the bionic ear developed by Professor Clark can be seen at the National Museum of Australia in Canberra, Australia. It is part of a collection acquired by the National Museum in 2009 and includes key elements that figured in the development of the bionic ear, including the prototype multi-channel cochlear implant received by Rod Saunders in 1978 (subsequently removed when it was replaced by an updated model).^[11]

In December 1984, the Australian cochlear implant was approved by the United States Food and Drug Administration to be implanted in adults in the United States. In 1990 the FDA lowered the approved age for implantation to two years, then 18 months in 1998, and finally 12 months in 2000,^[12] although off-label use has occurred in babies as young as 6 months in the United States and 4 months internationally.^{[citation needed]}

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 sound processor on their hip in a pack or small harness or wear the BTEs pinned to their collar, barrette or elsewhere.

On October 5, 2005, the first of three recipients was implanted with Cochlear's TIKI device, a totally implantable cochlear implant, in Melbourne, Australia.^[13] This was part of a research project conducted by Cochlear Ltd and the University of Melbourne Department of Otolaryngology under the umbrella of CRC HEAR to be the first cochlear implant system capable of functioning for sustained periods with no external components. The system is capable of providing hearing via the TIKI device in stand-alone mode (invisible hearing) or via an external sound processor. Although these recipients continue to use their devices successfully today, it will be many years before a commercial product becomes available.^[14]

Since hearing in two ears allows people to localize sounds (given synchronised AGCs) and to hear better in noisy environments, bilateral (both ear) implants are being investigated and used. Users generally report better hearing with two implants, and tests show that bilateral implant users are better at localizing sounds and hearing in noise.^[15] However, there is also evidence to suggest that the combination of one implant with an FM system provides better speech recognition in noise than two implants alone.^[16] Additionally, dynamic FM technology has been proven to outperform traditional FM when used with cochlear implants.^[17]

Nearly 3,000 people worldwide are bilateral cochlear implant users, including 1,600 children.^{[citation needed]} As of 2006, the world's youngest recipient of a bilateral implant was just over 5 months old (163 days) in Germany (2004).^[18]

Parts of the cochlear implant

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

The internal part of a cochlear implant (model Cochlear Freedom 24 RE)

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:

Type of hearing impairment

People with mild or moderate sensorineural hearing loss are generally not candidates for cochlear implantation. Their needs can often be met with hearing aids alone or hearing aids with an FM system. 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 a severe or profound sensorineural hearing loss.

The presence of auditory nerve fibers 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. Some individuals with severe auditory neuropathy may also benefit from cochlear implants.

Age of recipient

Post-lingually deaf adults, pre-lingually deaf children and post-lingually impaired people (usually children) who have lost hearing due to diseases such as CMV and meningitis, form three 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. The outcomes of individuals that have been deaf for a long period of time before implantation are sometimes astonishing, although more variable.

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.^[19]

Infant with cochlear implant

Another group of customers are parents of children born deaf who want to ensure that their children grow up with good spoken language skills. The brain develops after birth and adapts its function to the sensory input; absence of this has functional consequences for the brain, and consequently 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,^[20] though the critical period for utilizing auditory information does not close completely until adolescence. Additionally, a 2010 study into bilateral implantation showed that children who receive their first cochlear implant before the age of 1½ responded well to the second one, even if the second one was implanted as late as 9 years old. In contrast, children who got their implants at age 2½ years or later did not respond as well to the later second implant, regardless of when they received it.^[21] One doctor has said "There is a time window during which they can get an implant and learn to speak. From the ages of two to four, that ability diminishes a little bit. And by age nine, there is zero chance that they will learn to speak properly. So it’s really important that they get recognized and evaluated early."^[22]

The third group who will benefit substantially from cochlear implantation are post-lingual subjects who have lost hearing: a common cause is childhood meningitis. Young children (under five years) in these cases often make excellent progress after implantation because they have learned how to form sounds, and only need to learn how to interpret the new information in their brains.

Number of users

By the end of 2008, the total number of cochlear implant recipients had grown to an estimated 150,000 worldwide.^[23] A story in 2000 stated that one in ten deaf children in the United States had a cochlear implant, and that the projection was the ratio would rise to one in three in ten years.^[24]

Mexico had performed only 55 cochlear implant operations by the year 2000 (Berruecos 2000). Taiwan and China announced an approximately $270 million order for cochlear implant devices for children in 2006, which are being paid for by major healthcare organization based in Taipei. These cochlear implants are a donation by the Taiwanese organization^[25][26]