Hearing aids

Definition

A hearing aid is a device that can amplify sound waves in order to help a deaf or hard-of-hearing person hear sounds more clearly. There are two major types of hearing loss , conductive hearing loss and sensory hearing loss. Conductive hearing loss is often

mechanical in nature, resulting in external or middle ear problems. This type of hearing loss often can be corrected by medicine and/or surgery. Possible causes for conductive hearing loss include otitis media and otosclerosis. Sensory hearing loss is due to a disorder in the inner ear, specifically involving the cochlea. This type of hearing loss may be congenital or the result of an acquired condition, such as meningitis . Hearing aids are primarily used by patients with sensory hearing loss.

Purpose

Recent technology can help most people with hearing loss understand speech better and achieve better communication.

Precautions

It is important that a person being fitted for a hearing aid understand what an aid can and can not do. An aid can help a person hear better, but it will not return hearing to normal levels. Hearing aids boost all sounds, not just those the person wishes to hear. Especially when the source of sound is far away (such as up on a stage), environmental noise can interfere with good speech perception. And, while the aid amplifies sound, it does not necessarily improve the clarity of the sound. A hearing aid is a machine and can never duplicate the true sound that people with normal hearing experience, but it will help the person take advantage of the hearing that remains.

Description

More than one thousand different models of hearing aids are available in the United States. All of them include a microphone (to pick up sound), an amplifier (to boost sound strength), and a receiver or speaker (to deliver sound to the ear). All hearing aids are powered by a battery. Depending on the style, it is possible to add features to filter or block out background noise, minimize feedback, lower sound in noisy settings, or boost power when needed.

Hearing aids are either monaural, a hearing aid for one ear, or binaural, for two ears; more than 65% of all users have binaural aids. Hearing aids are divided into several different types:

• digital
• in-the-ear
• in-the-canal
• behind-the-ear
• on-the-body

Digital aids are sophisticated, expensive aids that borrow computer technology to allow a person to tailor an aid to a specific hearing loss pattern. Using miniature computer chips, the aids can selectively boost certain frequencies while leaving others alone. This means a person could wear such an aid to a loud party, and screen out unwanted background noise, while tuning in on one-on-one conversations. The aid

is programmed by the dealer to conform to the person's specific hearing loss. Some models can be programmed to allow the wearer to choose different settings depending on the noise of the environment.

In-the-ear aids are lightweight devices whose custom-made housings contain all the components; this device fits into the ear canal with no visible wires or tubes. It is possible to control tone but not volume with these aids, so they are helpful only for people with mild hearing loss. Some people find these aids are easier to put on and take off than behind-the-ear aids. However, because they are custom-fit to a person's ear, it is not possible to try on before ordering. Also, some people find them uncomfortable in hot weather.

In-the-canal aids fit far into the ear canal, with only a small bit extending into the external ear. The smallest is the MicroCanal, which fits out of sight down next to the eardrum and is removed with a small transparent wire. These aids are extremely expensive, but they are not visible, offer better acoustics, and are easier to maintain. They can more closely mimic natural sound because of the position of the microphone; this position also cuts down on wind noise. Because of their small size, these aids are harder to handle, and their battery is especially small and difficult to insert. Adjusting the volume may be hard, since a person must stick a finger down into the ear to adjust volume, and this very tiny aid does not have the power of larger aids.

Behind-the-ear aids include a microphone, amplifier, and receiver inside a small curved case worn behind the ear; the case is connected to the earmold by a short plastic tube. The earmold extends into the ear canal. Some models have both tone and volume control, plus a telephone pickup device. Many users think them unattractive and out of date, however, and those who wear glasses find that the glasses interfere with the aid's fit. Others do not have space behind the ear for the mold to fit comfortably. They do offer a few advantages.

Behind-the-ear aids:

• do not require as much maintenance
• are easily interchangeable if they need to be serviced
• are more powerful
• are easier to handle than smaller aids
• provide better sound quality
• are more reliable

Eyeglass models are the same as behind-the-ear devices, except that the case fits into an eyeglass frame instead of resting behind the ears. Not many people buy this type of aid, but those who do believe it is less obvious, although there is a tube that travels from the temple of the glasses to the earmold. It can be hard to fit this type of aid, and repairs can be problematic. Also, if the aid breaks, the person also loses the benefit of the glasses.

The crossover system type of hearing aid is often used in conjunction with the eyeglass model. The contralateral routing of signal (CROS) system features a microphone behind the ear that feeds the amplified signal to the better ear, eliminating “head shadow,” which occurs when the head blocks sound from the better ear. This type may help make speech easier to understand for people with a high-frequency loss in both ears.

A BI-CROS system uses two microphones (one above each ear) that send signals to a single amplifier. Sound then travels to a single receiver, which transfers it to the better ear via a conventional earmold.

On-the-body aids feature a larger microphone, amplifier, and power supply inside a case carried inside the pocket or attached to clothing. The receiver attaches directly to the earmold; its power comes through a flexible wire from the amplifier. Although larger than other aids, the on-the-body aids are more powerful and easier to adjust than other devices. While not popular for everyone, they are often used by those with a profound hearing loss, or by very young children. Some people who are almost totally deaf find they need the extra power boost available only from a body aid.

Cochlear implants, which are implanted through a surgical procedure, are taking hearing technology to a new level. Different from a hearing aid, cochlear implants are composed of an external portion (including a microphone worn behind the ear, a speech processor, and a transmitter) and an internal portion (including an implanted receiver and electrodes), a cochlear implant is designed to bypass damaged sound-sensing cells of the inner ear (cochlear hair cells) and provide electrical stimulation of the auditory nerve. The result is the sensation of sound for individuals who would otherwise be deprived. The best candidates for cochlear implants are individuals with profound hearing loss to both ears who have not received much benefit from traditional hearing aids and are of good general health. Children as young as 14 months have been successfully implanted.

Preparation

The first step in getting a hearing aid is to have a medical exam and a hearing evaluation. (Most states prohibit anyone selling a hearing aid until the patient has been examined by a physician to rule out medical problems.) After performing a hearing evaluation, an audiologist should be able to determine whether a hearing aid will help and which one will do the most good. This is especially important because aids can be very expensive (between $500 and $4,000) and are often not covered by health insurance. Hearing aids come in a wide range of styles and types, requiring careful testing to make sure the aid is the best choice for a particular hearing loss.

Some audiologists sell aids; others can make a recommendation, or provide a list of competent dealers in a patient's area. Patients should shop around and compare prices. In all but three states, hearing aids must be fitted and sold only by licensed specialists called dealers, specialists, dispensers, or dispensing audiologists.

The audiologist or hearing aid dealer will make an impression of the consumer's ear canals using a putty-like material, from which a personalized earmold will be created. It is the dealer's job to make sure the aid fits properly. The person may need several visits to find the right hearing aid and learn how to use it. The dealer will help the consumer learn how to put the aid on, adjust the controls, and maintain the device. The dealer should be willing to service the aid and provide information about what to do if sensitivity to the earmold develops. (Some people are allergic to the materials in the mold.)

Aftercare

Within several weeks, the wearer should return to the dealer to have the aid checked and to discuss the progress in wearing the aid. About 40% of all aids need some modification or adjustment in the beginning.

KEY TERMS

Audiologist —A person with a degree and/or certification in the areas of identification and measurement of hearing impairments and rehabilitation of those with hearing problems.

Cochlea —A conical bony structure or the inner ear; perforated by numerous openings for passage of the cochlear division of the acoustic nerve.

Conductive hearing loss —Hearing loss resulting from external or middle ear problems.

Eardrum —A paper-thin covering stretching across the ear canal that separates the middle and outer ears.

Middle ear —The small cavity between the eardrum and the oval window that houses the three tiny bones of hearing.

Oval window —A tiny opening at the entrance to the inner ear.

Sensory hearing loss —Hearing loss due to disorders of the inner ear.

Within the first month of getting an aid, the patient should make an appointment for a full hearing examination to determine if the aid is functioning properly.

Complications

While there are no medical complications to hearing aids, there is a risk associated with hearing aids: many people end up not wearing their aids because they say everything seems loud when wearing them. This may be because they have lived for so long with a hearing problem that they have forgotten how loud “normal” sound can be. Other potential problems with hearing aids include earmold discomfort and a build up of excess ear wax after getting a hearing aid.

Results

A hearing aid boosts the loudness of sound, which can improve a person's ability to understand speech.

Caregiver concerns

Physicians, audiologists, and nurses are involved in the diagnosis and treatment of hearing loss. Audiologists prescribe, dispense, and service hearing aids.

Resources

BOOKS

Carmen, Richard. The Consumer Handbook on Hearing Loss and Hearing Aids. New York: Auricle Ink Publishers, 1997.

Turkington, Carol A. The Hearing Loss Sourcebook. New York: Penguin, 1997.

PERIODICALS

Dickinson, Ben. “30/40/50: Listen Up While You Still Can.” Esquire 129 (January 1, 1998): 101.

ORGANIZATIONS

American Academy of Otolaryngology-Head and Neck Surgery. One Prince St., Alexandria, VA 22314-3357. (703) 836-4444. http://www.entnet.org.

American Speech-Language-Hearing Association (ASHA). 10801 Rockville Pike, Rockville, MD 20852. (888) 321 ASHA. http://www.asha.org.

National Institute on Deafness and Other Communication Disorders. 1 Communication Avenue, Bethesda, MD 20892-3456. (800) 241-1044. http://www.nidcd.nih.gov.

Self Help for Hard of Hearing People, Inc. 7910 Woodmont Ave, Suite 1200, Bethesda, MD 20814. (301) 657-2248. TTY: (301) 657-2249. http://www.shhh.org.

OTHER

“Cochlear Implants.” National Institutes on Deafness and Other Communication Disorders. 2001. July 6, 2001. http://www.asha.org/hearing/rehab/cochlear_implant.cfm.

“Hearing Loss.” Virginia Merrill Bloedel Hearing Research Center. 2001. July 25, 2001. http://depts.washington.edu/hearing/Hearing%20Loss.html.

Carol A. Turkington