Indications and Procedures (Magill’s Medical Guide, Sixth Edition)
Hearing loss is one of the most common conditions affecting older adults, but it is not limited to that age group. In the early twenty-first century, it was estimated that about one in ten individuals in the United States had a significant hearing loss and that 120 million people worldwide had hearing loss significant enough to interfere with communication. In the United States, approximately one million people each year purchase hearing aids. These devices were developed to help those people affected by hearing loss ranging from mild to severe and resulting from a number of causes. The most common type of hearing loss, sensorineural, is linked to a variety of physical and psychosocial dysfunctions (isolation, depression, hypertension, and stress), as well as illnesses such as ischemic heart disease and arrhythmias.
Over the years, hearing aids have evolved in several ways. Two major trends have been in signal processing and size. In the 1960’s, the best available hearing aids were limited to help in quiet only; in loud situations, they made things worse. Therefore, it was common practice to remove them around noise. They produced sound like cheap transistor radios. Starting in the 1980’s and 1990’s, advanced circuitry has offered consumers improved quality of hearing in quiet as well as some increased ability to hear in noise; sound distortion is now minimal. Certain hearing aids can be electronically...
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Uses and Complications (Magill’s Medical Guide, Sixth Edition)
One of the biggest impediments to hearing aid use is patient reactions to hearing loss. Many people try to cover up the fact that they have hearing difficulties, and when hearing loss is confirmed, they experience a wide range of emotions, from horror, denial, disbelief, and withdrawal to embarrassment, sadness, resentment, and gradual acceptance and coping. People’s coping skills and behavior patterns vary, in part because hearing loss generally occurs gradually and may take a long time to be recognized.
For those who embrace hearing aids, a variety of technological and cosmetic choices are available. A number of options exist regarding hearing aid style: behind-the-ear, custom in-the-ear, in-the-canal, and the smallest, the completely in-canal hearing aid. In addition to aesthetic considerations and sound fidelity, one’s anatomy and manual dexterity may dictate the style that is most effective and efficient. The degree of hearing loss and other medical conditions are also important factors when evaluating the best hearing aid.
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Perspective and Prospects (Magill’s Medical Guide, Sixth Edition)
Hearing aid technology has improved such that patients with mild to moderate hearing loss will be candidates for hearing aids and those with severe loss will be candidates for hearing aids or cochlear implants, depending upon how well they function with a particular device. Patients with profound hearing loss will benefit best from cochlear implants.
Initially, only those patients who were completely deaf in both ears were considered candidates for cochlear implants. With significant improvements in implant technology, however, the benefits gained by implanted patients, both children and adults, have markedly improved. This, in turn, has led to a broadening of criteria for implant patients. Select patients with severe hearing loss who receive some benefit from hearing aids are considered possible implant candidates.
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For Further Information: (Magill’s Medical Guide, Sixth Edition)
Biderman, Beverly. Wired for Sound: A Journey into Hearing. Toronto, Ont.: Trifolium Books, 1998.
Carmen, Richard, ed. The Consumer Handbook on Hearing Loss and Hearing Aids: A Bridge to Healing. 3d rev. ed. Sedona, Ariz.: Auricle Ink, 2009.
Dillon, Harvey. Hearing Aids. New York: Thieme, 2001.
Romoff, Arlene. Hear Again: Back to Life with a Cochlear Implant. New York: League for the Hard of Hearing, 1999.
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Hearing Aids (Encyclopedia of Medicine)
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.
Recent technology can help most people with hearing loss understand speech better and achieve better communication.
It's important that a person being fitted for a hearing aid understand what an aid can and can't do. An aid can help a person hear better, but it won't 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 doesn't 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.
More than 1,000 different models are available in the United States. All of them include a microphone (to pick up sound), amplifier (to boost sound strength), a receiver or speaker (to deliver sound to the ear), and are powered by a battery. Depending on the style, it's possible to...
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Hearing Aids (Encyclopedia of Nursing & Allied Health)
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.
Recent technology can help most people with hearing loss understand speech better and achieve better communication.
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.
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 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.
- 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.
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 puttylike 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.)
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.
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.
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.
A hearing aid boosts the loudness of sound, which can improve a person's ability to understand speech.
Health care team roles
Physicians, audiologists, and nurses are involved in the diagnosis and treatment of hearing loss. Audiologists prescribe, dispense, and service hearing aids.
Audiologist 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 conical bony structure or the inner ear; perforated by numerous openings for passage of the cochlear division of the acoustic nerve.
Conductive hearing lossearing loss resulting from external or middle ear problems.
Eardrum paper-thin covering stretching across the ear canal that separates the middle and outer ears.
Middle earhe small cavity between the eardrum and the oval window that houses the three tiny bones of hearing.
Oval window tiny opening at the entrance to the inner ear.
Sensory hearing lossearing loss due to disorders of the inner ear.
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.
Dickinson, Ben. "30/40/50: Listen Up While You Still Can." Esquire 129 (Jan. 1, 1998): 101.
American Academy of Otolaryngology-Head and Neck Surgery. One Prince St., Alexandria, VA 22314-3357.(703) 836-4444. <<a href="http://www.entnet.org">http://www.entnet.org>.
American Speech-Language-Hearing Association (ASHA). 10801 Rockville Pike, Rockville, MD 20852. (888) 321-ASHA. <<a href="http://www.asha.org">http://www.asha.org>.
National Institute on Deafness and Other Communication Disorders. 1 Communication Avenue, Bethesda, MD 20892-3456. (800) 241-1044. <<a href="http://www.nidcd.nih.gov">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. <<a href="http://www.shhh.org">http://www.shhh.org>.
"Cochlear Implants." National Institutes on Deafness and Other Communication Disorders. 2001. 6 July 2001. <<a href="http://www.asha.org/hearing/rehab/cochlear_implant.cfm">http://www.asha.org/hearing/rehab/cochlear_implant.cfm>.
"Hearing Loss." Virginia Merrill Bloedel Hearing Research Center. 2001. 25 July 2001. <<a href="http://depts.washington.edu/hearing/Hearing%20Loss.html">http://depts.washington.edu/hearing/Hearing%20Loss.html>.
Carol A. Turkington
Hearing Aid (How Products are Made)
The hearing aid is an instrument that amplifies sounds, particularly speech, for people with hearing impairments. It may be worn comfortably behind the ear, in the outer ear, within the ear canal, in the frames of eyeglasses, or against the body or in the clothing. The main elements of the aid are a microphone, an electronic amplifier to make the sound louder, an earphone or receiver, and an ear mold or plastic shell that serves to couple acoustic energy (sound) from the earphone to the eardrum either directly or through plastic tubes. The sound is converted to an electrical signal, amplified, then reconverted to acoustic energy in the inner ear. A battery, the typical power source, can also be contained in the shell.
The microphone and earphone together form a transducer and determine the performance of the aid over a range of frequencies. The adjustment of tone (low and high frequencies) and gain (volume) can be either manual or automatic so that the user can hear enhanced sounds within a comfortable tolerance level.
The earliest hearing aids were ear trumpets invented sometime in the 17th century. They were long horns with one large opening at one end and a smaller opening at the other end, which was placed in the ear. The principle behind this instrument being that sound pressure waves entering the large end are condensed into smaller volume, thereby increasing the audible sound pressure.
The first electronic aid was a telephone invented by Alexander Graham Bell in 1876 that converted sound pressure waves to a current and then back to waves. By the 1920s, a more sophisticated telephone-type aid was developed resembling the modern hearing aid with a microphone, electrical circuit, diaphragm, and battery. With the invention of the transistor in 1948, the size and weight of the aid was further greatly reduced. Today, tiny aids placed in the ear canal are barely visible to others, offering great cosmetic appeal to the user. The miniaturization of the hearing aid continues to be an area of research and experimentation. Unfortunately, the smaller the hearing aids become, the greater the manual dexterity required of a user to work the controls.
The Manufacturing Process
Fabricating a hearing aid takes about two hours. Making hearing aids is a customized process requiring skilled technicians to operate magnification glasses and microscopes in a microminiature manufacturing environment. The tools are generally hand-held and the tasks demand precision movements. The assembler must pay close attention to the wiring diagram and assembly prints so that he or she wires it to produce exact results.
Before fabrication begins, the user is screened by a trained professional. The screening includes a hearing test, and the results are used to create an audiogram covering a variety of parameters. At the screening stage, an impression or mold of the user's outer ear is also taken. The audiogram and the impression are integral to the manufacturing process.
- 1 All order dataesired product features and the results of the audiogramre entered in a computer to determine the operating range for the hearing aid, specifically which levels of amplification are required for the user. For some manufacturers, the computer also selects the electronic circuitry to be used. Typically an order card will be prepared and sent to the production line along with the ear impression. A parts card is also printed and sent to the stock room, where the various components are stored.
Vacuum form of impression
- 2 In this step, a form or reverse copy of the impression of the outer ear and ear canal is produced. A sheet of clear vinyl is placed over the impression; then heat is applied. When cooled, the impression is removed from the vinyl form and trimmed. Next the impression is dipped in hot wax, giving it a smooth, paper-thin coating for the casting step.
Cast of finished impression
- 3 Here a technician will place the impression on a metal plate and place rings around it. A clear liquid colloid or particle suspension is poured into the rings, immersing the impression. The liquid is allowed to cure into a rubbery silicone consistency. Lastly, the impression is pulled out of the gel.
Creating the shell
- 4 The shell or outer casing of the hearing aid is made from this mold. The mold is first heated in 110°F (43°C) water, and air is blown through it to clear away any impurities. At this point, a technician will mix liquid acrylic of equal parts monomer and polymer (for a structurally sound shell) and add the desired pigment to give the shell a pink, tan, or brown color. The technician pours the liquid into the heated colloid mold and after ten seconds, pours off any excess, leaving a thin acrylic shell inside the mold. After 10 minutes of cooling, the technician pulls from the mold a shell that is a perfect replica of the raw impression of the ear canal.
Building the hearing aid into the shell
- 5 After a technician grinds off the excess flanges from the shell, he will add a vent or opening. A small piece of silicon wire shaped to the vent size is run through the inside of the shell and pulled out. The technician drills holes into the canal end of the shell for the receiver tube. After that, the outside of the shell will be buffed to a
Creating the microminiature circuits
- 6 The components and circuits are run on a ceramic substrate base of various designs. The substrate is made by a screen printing technique that alternates layers of conductive and insulating materials, depending on the engineered design. The conducting layer contains gold and silver, and the insulating layers contain silicon compounds. Between the printing of each layer, the substrate is passed by a conveyor through a furnace, where it bakes for two hours at 850°F (454°C). This seals the layers and creates the color patterns characteristic of printed circuit boards, only on a smaller scale. The various electronic components are bonded by hand to the gold and silver parts on both sides of the substrate. A technician will interconnect the devices using gold wire of .001 inch (.025 mm) thickness. Lastly, the components are sealed in an epoxy paste and heat-hardened.
Assembling the electronic hardware
- 7 Working from the parts card or bill of materials determined at the outset of production, a technician assembles the electronic hardware on the face plate where holes have been drilled for mounting the microphone, amplifier, battery compartment, and volume control, all hand-wired with colors for traceability. The wires are soldered into place. After this, the receiver is mounted into the shell and a preliminary hearing check made on the instrument.
Sealing and finishing
- 8 In the final production steps, the parts are carefully packaged to avoid interferences. A plastic cement is brushed on while the technician performs a listening check to make sure there is no oscillation in the sound quality. Once the cement dries, excess face plate is cut away and the remaining edge ground off with a hand lathe. Finally the aid is buffed and shined to a high gloss and manufacturing is complete. The aid is now ready for final testing.
Quality Control and Testing
Quality control measures are checked throughout production, some of which have been discussed in the process description above. In addition, the shell is given a serial number after it is constructed for tracking purposes. Appearance is important, and a cosmetic check is made as well as a final function check.
Hearing aids are tested using a computerized ANSI (American National Standards Institute) program that analyzes the production parameters and produces a performance chart. A technician reviews the chart on-screen, checking tolerance levels and other specifications. He or she will print a copy of the results and include it with the finished hearing aid.
The future of hearing aids seems to lie in miniaturization. Today's technology can produce aids the size of a fingertip. Also a recent development, customized digitally programmable aids using microchips found in computers allow users to rapidly switch settings to accommodate different situations. Outdoor events, crowded restaurants, and intimate meetings, each with different sound patterns, can be programmed in the chips. This minimizes the quick adjustments some users must make when they move into a new environment. These custom aids can cost $2,000 each.
Where To Learn More
Levitt, Harry, ed. Recent Advances in Sensory Aids for Hearing Impairment. Diane Publishing Company, 1994.
Neuman, Arlene C. Hearing Aids: Recent Developments. York Press, Inc., 1993.
Pascoe, David P. Hearing Aidsi>Who Needs Them?: What They Can Do for You, Where to Buy Them, How to Use Them. Big Bend Books, 1991.
Staab, Wayne J. Hearing Aid Handbook. Tab Books, 1978.
Aldersey-Williams, Hugh. "Invisible Hearing Aid Gives Eardrums Good Vibrations." New Scientist, August 1, 1992, p. 18.
Brietzke, C.E. "Listen Up!" Saturday Evening Post, September-October 1993, p. 36, 92-93.
Pierson, John. "Form Plus Function: In-the-Ear Hearing Aids with In-Your-Face Colors." The Wall Street Journal, October 28, 1994, B1.