Factors That Affect Outcome with Cochlear Implants

The person’s age when he became deaf (adults who have been deaf since birth or early childhood tend to benefit less from an implant, especially if they haven’t relied on hearing for communication in the past)

The length of time that the person was deaf before receiving an implant (the shorter the time, the greater the chance of success)

The person’s past use of hearing aids (past use increases the probability of success, because the brain has been receiving sound stimulation)

The person’s age at the time of implantation (very young children do best because their brains are more adaptable or “plastic”; however, adults, even elderly adults, often do remarkably well)

The physical condition of the cochlea and CN VIII (malformation of or damage to the cochlea or CN VIII reduces the probability of success)

The listener’s auditory skills before the implant (people with more residual hearing and better speech perception tend to do better with implants)

The presence of other medical conditions (medical conditions can make surgery, postsurgical recovery, and rehabilitation more difficult)

The person’s expectations (an implant doesn’t restore normal hearing, and those with that expectation will be disappointed)

The person’s motivation

Family support

Participation in a hearing rehabilitation program following surgery

COCHLEAR IMPLANT SURGERY

The surgical procedure, performed under general anesthesia, typically takes 2 to 5 hours. Patients usually go home the same day or the next morning. A “bed” for the receiver is hollowed out of the mastoid bone behind the ear, and an opening is made into the cochlea through the middle ear. The receiver is then anchored in the mastoid bone, and the flexible electrode array is threaded through the spirals of the cochlea. Generally, an audiologist in the operating room tests the electrodes to be sure they’re working before the incision is closed. Most people resume normal activity within a week. All surgery involves risks, but those associated with cochlear implant surgery are comparatively small.

DEVICE ACTIVATION AND PROGRAMMING

After the incision has healed, the patient returns to the cochlear implant center to have the implant activated. The audiologist fits the speech processor and transmitter to the user, turns on the device, and speaks. Voila!` Hearing! This is an unforgettable (and often very emotional) moment for the patient and family. The audiologist then connects the processor to a special computer with special software (specific to each implant manufacturer) and programs the device.

Each implant manufacturer offers several processing or coding strategies from which the audiologist can choose. A coding strategy is a set of rules that determine how the processor translates the characteristics of incoming sounds (for example, pitch, loudness, and timing) into patterns of electrical pulses and how the electrodes are stimulated. Implant manufacturers are continually developing new coding strategies and improving existing ones.

Electrodes are activated one by one; the audiologist sets each electrode’s minimal and maximal current levels, ensuring that incoming sound information will be loud enough to hear but not loud enough to cause discomfort. Like fine tuning hearing aids, mapping is an ongoing process rather than an event; it can take multiple visits to achieve the best map, although this varies. Some processors allow several programs to be stored in memory so that the user can select the program that best suits the listening environment.

Implant centers provide assistance, information, and support to users and their families long after device activation and programming. Rehabilitation may be provided by professionals at the implant center or arranged closer to home in consultation with implant team members. Learning to listen through a cochlear implant is an adjustment that often takes time, instruction, and practice. Rehabilitation is designed to help the user adjust to a new type of “sound” and learn to use the technical capabilities of the device. The rehabilitation program typically focuses on auditory training, perhaps combined with speechreading practice. The program should also include instruction about assistive listening technology, communication strategies, and maintaining the implant. For some, it might also include personal adjustment counseling as the user makes the transition from being deaf to being hard of hearing. Family counseling is another important component. Finally, the implant center may offer a support group in which implant candidates can meet experienced users and connect with other new users. In addition to implant centers, implant manufacturers offer extensive and personalized support services that can be accessed online or by telephone.

CHOOSING AMONG COCHLEAR IMPLANT DEVICES

Like hearing aids, cochlear implants have become smaller and more technically sophisticated over the years. Initially, all processors were worn on the body (usually in a pocket or clipped to a belt) with a cable connecting the processor to the transmitter on the head. Today, all manufacturers offer ear-level processors that look something like BTE hearing aids. Although ear-level devices are less cumbersome, body-worn processors, with larger controls, may be preferred by people with vision or dexterity problems. Like hearing aids, processors offer increasingly sophisticated technical features that automatically adjust to improve listener comfort and speech understanding in difficult listening situations.

If you become a cochlear implant candidate, you might be asked to choose the device with which you’ll be implanted. Three manufacturers have a presence in the United States: Advanced Bionics, Cochlear Americas, and Med-El. Some implant centers work with only one manufacturer’s implant, whereas others work with all three devices. Users of each device show a wide range of performance; however, studies have shown that the same level of success is possible with any of them. Cochlear implants are designed to last a lifetime. All three implants have a low failure rate. This is important, because internal device failure generally means a second surgery. All three implants are built to handle future upgrades and enhancements. As new technologies emerge, users are able to take advantage of them without the need for further surgery. All three implants cost about the same. The total cost of evaluation, surgery, the device itself, and rehabilitation ranges from $45,000 and $70,000. Most insurance companies, Medicare, and the Department of Veterans Affairs cover part or all of the cost.

There are important technical differences in the way each device processes and codes incoming sounds; however, a distinction that’s probably more apparent to the user is the manner by which each device connects to external sound sources. All three processors can be connected to telephones, FM systems, induction loops, televisions, computer speakers, portable CD/DVD players, and personal listening devices such as iPods. The means for making these connections differs by manufacturer and speech processor style. Another important distinction is the implant’s battery supply; implants use considerable power. Devices use rechargeable batteries, disposable batteries, or both.

There’s no evidence that one implant is inherently better than the others. Members of your implant team can discuss the relative advantages and disadvantages of the implant devices that are available to you.

Factors to Consider When Choosing an Implant Device

Device failure rate

Device durability

Weight of the external components

Comfort (try the external components on)

Appearance of external components

Ability to see and adjust controls on the processor

Number of coding strategies available

Flexibility of programming

Ability to incorporate future technological improvements

Availability of technical features designed to improve speech understanding in difficult listening conditions

Type of batteries used (rechargeable or disposable) and their cost

Battery life

Ease of connecting to the telephone and assistive technology

Customer service

Warranty

AUDITORY BRAINSTEM IMPLANTS

Most of the problems that cause deafness lie within the cochlea. Damage to the cochlea results in sensory hearing loss. A problem that results in damage to CN VIII can cause neural hearing loss. For example, surgery to remove a tumor on CN VIII might result in permanent and total deafness in one ear. People affected by Neurofibromatosis Type II (NF2) often develop CN VIII tumors on both sides, and removal of the tumors can result in total bilateral deafness. Hearing aids and cochlear implants are ineffective because CN VIII is unable to carry sound information to the brain. Auditory brainstem implants are designed to treat this type of deafness. They involve placement of a multichannel electrode on the cochlear nucleus, the site in the lower brainstem where CN VIII normally delivers the sound information it carries. A speech processor worn outside the body collects sounds from the environment and codes them; electrical stimulation of the cochlear nucleus results in the perception of sound. The ability to understand speech with this device is somewhat limited at this time.

CURRENT AND FUTURE TRENDS

When single-channel cochlear implants first became available in the mid-1980s, only people with adult-onset, profound hearing loss and speech perception scores of less than 10 percent were considered candidates. Since then, outcomes have improved, and candidacy criteria have broadened considerably, enabling infants, children, and adults with more hearing and better speech perception to benefit from this technology. It’s expected that hearing criteria will continue to expand in the future and that devices will continue to become smaller and more sophisticated. Future devices might be totally implantable, with no need for external components at all.

Bilateral Cochlear Implants

Hearing with two ears has important advantages (see Chapter 7). For example, when hearing is approximately the same in both ears (either naturally or through two hearing aids), slight differences in the timing and loudness of a sound arriving at the two ears allow us to localize its source. Hearing with two ears also enables us to separate the signal of interest from background noise; the brain compares the signals coming from the two ears and filters out much of what is unwanted. Until recently, cochlear implants have been used in only one ear. Because of concerns about the destruction of

hearing in the implanted ear and the unknown effects of long-term electrical stimulation, the goal was to save residual hearing in the nonimplanted (better) ear for future advances in hearing science. However, implant outcomes are now excellent for most users, and many implant centers are offering bilateral implants (implants in both ears). Research shows that bilaterally implanted listeners have improved localization ability, better hearing in noise, and a greater sense of well-being. Among other things, candidacy for bilateral implants depends on how much hearing there is in the better ear. Of the 100,000 people who’ve been implanted thus far, perhaps 15 percent have been implanted bilaterally. Insurance companies are beginning to cover the cost of two implants.

Electro-acoustic Stimulation

Candidacy criteria for cochlear implants are now being broadened to include people who have severe or profound high-frequency hearing loss with mild or moderate low-frequency loss. These listeners often do quite well wearing hearing aids in quiet, but they have difficulty understanding speech in noisy situations because they’re missing critical high-frequency information. Hearing aids may be unable to amplify high-frequency sounds because there aren’t enough functioning hair cells in high-frequency regions of the cochlea to pass information along to CN VIII (these areas are sometimes referred to as cochlear dead regions). In the past, these listeners derived limited benefit from hearing aids, yet didn’t qualify for cochlear implants because of their “good” low-frequency hearing. Implant manufacturers are now testing hybrid devices that combine hearing aid and cochlear implant technologies, and there are new surgical techniques that allow low-frequency residual hearing to be preserved (for example, use of a “short” electrode array that doesn’t reach all the way to low-frequency regions of the cochlea). The listener wears a device that amplifies the low frequencies acoustically and stimulates the middle and high frequencies electrically. Research suggests that patients implanted with hybrid devices have better speech understanding in noise and improved music perception. Although there’s some indication that it might be more difficult to adjust to electro-acoustic stimulation than to either a hearing aid or cochlear implant alone, this technology appears to represent a major advance in the treatment of high-frequency hearing loss.

Bimodal Fittings

A bimodal fitting is one in which a hearing aid is worn on one side (acoustic hearing) and a cochlear implant (electrical stimulation) is worn on the other. Initially, bimodal fittings were discouraged because of concerns about the brain’s ability to integrate two different types of input (which could result in binaural interference). In addition, implant criteria required that there be little hearing in the nonimplanted (better) ear. However,

improvements in cochlear implant performance have led to expanded candidacy criteria, meaning that people with considerably more hearing in both ears now receive implants. Researchers have found that the two inputs actually provide complementary information, resulting in better speech perception in noise and improved localization. Listeners report that hearing is more natural and sound quality is better with a hearing aid in the nonimplanted ear. The arrangement also prevents auditory deprivation (over time, speech perception in the nonimplanted ear may deteriorate due to lack of stimulation), and provides the listener with a backup device should one fail. Disadvantages include greater cost (two devices cost more than one) and more maintenance. Adjustment to bimodal hearing takes more time and skill, and a few listeners probably will experience binaural interference. In the future, however, bimodal fittings may be recommended for all listeners with unilateral implants who have usable hearing in the nonimplanted ear, even if the loss is severe or profound. For many people, this solution will be more practical and much less expensive than two implants.

Optical Stimulation

Researchers are exploring the use of light, rather than electrical signals, to stimulate CN VIII. In contrast to electrical stimulation, in which a broad spread of current stimulates a broad range of nerve fibers that are responsive to a broad range of frequencies, an optical cochlear implant could stimulate nerve fibers with greater precision. Stimulation that is more frequency specific should result in a more accurate representation of sound being sent to the brain. This in turn should result in clearer hearing, including improved speech perception in background noise. Optical stimulation might also decrease tissue damage, because electrodes wouldn’t touch neural tissues to stimulate them.

Auditory Nerve Implants

Researchers are also exploring the possibility of implanting an ultrathin electrode array directly in CN VIII.1 Conventional electrode arrays are implanted in the cochlea, which is separated from auditory nerve fibers by fluid and bone; according to researchers, the effect is like talking to someone through a closed door. The intraneural implant would eliminate those barriers. This type of implant has the potential to activate nerve fibers associated with specific frequencies more precisely and reduce interference among electrodes when they’re stimulated simultaneously, both of which should increase hearing clarity. In addition, it could be better in terms of preserving low-frequency residual hearing. If the initial success with animal studies is borne out, a human auditory nerve implant could be 5 to 10 years away.

Questions to Ask When Considering a Cochlear Implant2,3

How well should I expect to hear and understand speech with the implant?

Which ear should be implanted?

Am I a candidate for two implants?

What is the surgeon’s experience with implant surgery? (How many surgeries has she performed? How many times has she implanted the device that I will receive?)

What are the surgical risks?

How long will the surgery take?

How long will I be in the hospital?

How will I feel when I wake up after surgery?

How much work will I miss?

When can I go back to my exercise routine?

Do I need a meningitis vaccination?

How often do I need to return to the implant center after surgery?

How much time should I plan to devote to postsurgical rehabilitation?

Which implant is best for me?

How does the implant connect to the telephone and assistive listening devices?

What kind of batteries does the device use? How much do the batteries cost?

Can I use a hearing aid in the other ear?

Does insurance cover the surgery, the device, and rehabilitation?