Audiology and hearing aids

Summary

Audiology is the study of hearing, balance, and related ear disorders. Hearing disorders may be the result of congenital abnormalities, trauma, infections, exposure to loud noise, some medications, and aging. Some of these disorders may be corrected by hearing aids and cochlear implants. Hearing aids amplify sounds so damaged ears can discern them. Some aids fit over the ear with the receiver behind the ear, and some fit partially or completely within the ear canal. Cochlear implants directly stimulate the auditory nerve, and the brain interprets the stimulation as sound.

Definition and Basic Principles

Audiology is the study of hearing, balance, and related ear disorders. Audiologists are licensed professionals who assess hearing loss and related sensory input and neural conduction problems and oversee treatment of patients.

Hearing is the ability to receive, sense, and decipher sounds. To hear, the ear must direct sound waves inside, sense the sound vibrations, and translate sensations into neurological impulses the brain can recognize.

The outer ear funnels sound into the ear canal. It also helps the brain determine the direction from which the sound is coming. When the sound waves reach the ear canal, they vibrate the eardrum. These vibrations are amplified by the eardrum's movement against three tiny bones behind the eardrum. The third bone rests against the cochlea which transmits the sound and creates waves in the fluid of the cochlea.

The cochlea is a coiled, fluid-filled organ that contains thirty thousand hairs of different lengths that resonate at different frequencies. Vibrations of these hairs trigger complex electrical patterns that are transmitted along the auditory nerve to the brain, where they are interpreted.

Background and History

The first hearing aidspopularized in the sixteenth centurywere large ear trumpets. In the nineteenth century, small trumpets or ear cups were placed in acoustic headbands that could be concealed in hats and hairstyles. Small ear trumpets were also built into parasols, fans, and walking sticks.

Electrical hearing devices emerged at the beginning of the twentieth century. These devices had an external power source and could provide greater amplification than mechanical devices. The batteries were large and difficult to carryhe carrying cases were often disguised as purses or camera cases. Zenith introduced smaller hearing aids with vacuum tubes and batteries in the 1940s.

In 1954, the first hearing aid with a transistor was introduced. This led to hearing aids that were made to fit behind the ear. Components became smaller and more complex, leading to the marketing of devices that could fit partially into the ear canal in the mid-1960s . Others that could fit completely into the ear canal became available in the 1980s.

How It Works

Audiologists are concerned with three kinds of hearing loss. The first is conductive hearing loss, in which sound waves are not properly transmitted to the inner ear. A second type is sensorineural hearing loss where the cochlea or the auditory nerve is damaged. Third is mixed hearing loss which is a combination of these.

Conductive Hearing Loss

Otosclerosis, or the inefficient movement of the three bones in the middle ear, results in hearing loss from poor conduction. This disease is treatable with surgery to replace the malformed, misaligned bones with prosthetic pieces to restore conductance of sound waves to the cochlea.

Meniere's disease is thought to result from an abnormal accumulation of fluid in the inner ear in response to allergies, blocked drainage, trauma, or infection. Its symptoms include vertigo with nausea and vomiting and hearing loss. The first line of treatment is motion sickness and antinausea medications. If the vertigo persists, treatment with a Meniett pulse generator may result in improvement. This device safely applies pulses of low pressure to the middle ear to improve fluid exchange.

Hearing loss may result from physical trauma, such as a fracture of the temporal bone that lies just behind the ear or a puncture of the eardrum. These injuries typically heal on their own, and in most cases, the hearing loss is temporary.

A gradual buildup of earwax may block sound from entering the ear. Earwax should not be removed with a cotton swab or other object inserted in the ear canal as this may result in infection or further impaction. Earwax should be softened with a few drops of baby oil or mineral oil placed in the ear canal twice a day for a week and then removed with warm water squirted gently from a small bulb syringe. Once the wax is removed, the ear should be dried with rubbing alcohol. In stubborn cases, a physician or audiologist may have to perform the removal.

Foreign bodies in the ear canal, most commonly toys or insects, may block sound. If they can be seen clearly, they may be carefully removed with tweezers. If they cannot be seen clearly or moved, they may be floated out. For toys, the ear canal is flooded with warm water squirted gently from a small bulb syringe. For insects, the ear canal should first be filled with mineral oil to kill the bug. If the bug still cannot be seen clearly, the ear canal may then be flooded with warm water squirted gently from a small bulb syringe. Once the object is removed, the ear canal should be dried with rubbing alcohol.

Sensorineural Hearing Loss

Some medications have adverse effects on the auditory system and may cause hearing loss. These medications include large doses of aspirin, certain antibiotics, and some chemotherapy agents. Doses of antioxidants such as vitamin C, vitamin E, and ginkgo biloba may ameliorate these ototoxic effects.

Exposure to harmful levels of noise, either over long periods or in a single acute event, may result in hearing loss. If the hair cells in the cochlea are destroyed, the hearing loss is permanent. Hearing aids or cochlear implants may be necessary to compensate.

An acoustic neuroma is a noncancerous tumor that grows on the auditory nerve. It is generally surgically removed, although patients who are unable to undergo surgery because of age or illness may undergo stereotactic radiation therapy instead.

Presbycusis is the progressive loss of hearing with age as a result of the gradual degeneration of the cochlea. It may be first noticed as an inability to hear high-pitched sounds. Hearing aids are an appropriate remedy.

Mixed Hearing Loss

Infections of the inner ear can occur by the viruses that cause mumps, measles, and chickenpox and infections of the auditory nerve. The viruses that cause mumps and rubella may cause permanent hearing loss. Because fluid builds up and viruses do not respond to antibiotics, viral ear infections may require surgical treatment. In a surgical procedure called myringotomy, a small hole is created in the eardrum to allow the drainage of fluid. A small tube may be inserted to keep the hole open long enough for drainage to finish.

Some children are born with hearing loss as the result of congenital abnormalities. Screening to determine the nature and severity of the hearing loss is difficult. Children are not eligible for cochlear implants before the age of twelve months. Young children often do well with behind-the-ear hearing aids, which are durable and can grow with them.

Applications and Products

Audiological products consist mainly of hearing aids and cochlear implants.

Hearing Aids

Although hearing aids take many forms, basically, all of them consist of a microphone that collects sound, an amplifier that magnifies the sound, and a speaker that sends it into the ear canal. They require daily placement and removal, and must be removed for showering, swimming, and battery replacement. Most people do not wear them when sleeping.

Hearing aids that sit behind the ear consist of a plastic case, a tube, and an earmold. The case contains components that collect and amplify the sound, which is then sent to the earmold through the tube. The earmold is custom-made to fit comfortably. This type of hearing aid is durable and well suited for children, although their earmolds must be replaced as they grow.

Hearing aids that sit partially within the ear canal are self-contained and custom-molded to the ear canal, so they are not recommended for growing children. Because of the short acoustic tube that channels the amplified sound, they are prone to feedback, which makes them less than ideal for people with profound hearing loss. Newer models offer feedback cancellation features.

Hearing aids that sit completely within the ear canal are self-contained and custom-molded. However, thin electrical wires replace the acoustic tube, so this type of hearing aid is free of feedback and sound distortion. They are not well suited for elderly people because their minimal size limits their volume capabilities.

The first hearing aids were analogue, a process that amplified sound without changing its properties. Although amplification was adjustable, the sound was not sorted, so background noise was also amplified. New hearing aids are digital, a process in which sound waves are converted into binary data that can be cleaned up to deliver clearer, sharper sounds.

The choice of hearing aid depends on the type and severity of hearing loss. Hearing aids will not restore natural hearing. However, they increase a person's awareness of sounds and the direction from which they are coming and heighten discernment of words.

Cochlear Implants

The US Food and Drug Administration approved cochlear implants in the mid-1980s. A cochlear implant differs from a hearing aid in its structure and its function. It consists of a microphone that collects sound, a speech processor that sorts the incoming sound, a transmitter that relays the digital data, a receiver/stimulator that converts the sound into electrical impulses, and an electrode array that sends the impulses from the stimulator to the auditory nerve. Hearing aids compensate for damage within the ear; cochlear implants avoid the damage within the ear altogether and directly stimulate the auditory nerve.

Whereas hearing aids are completely removable, cochlear implants are not. The internal receiver/stimulator and electrode array are surgically implanted. Three to six weeks after implantation, when the surgical incision has healed, the external portions are fitted. The transmitter and receiver are held together through the skin by magnets. Thus, the external portions may be removed for sleep, showering, and swimming.

Careers and Course Work

Audiologists are licensed professionals but not medical doctors. Physicians who specialize in ears, nose, and throat (ENT) disorders are called otorhinolaryngologists. Audiologists must have a doctoral (Au.D.) degree. State licensure is required to practice in all fifty states; licensure requirements vary by state. To obtain a license, an applicant must graduate from an accredited audiology program, accumulate 300 to 375 hours of supervised clinical experience, and pass a national licensing exam. To get into a graduate program in audiology, applicants must have had undergraduate courses in biology, chemistry, physics, anatomy, physiology, math, psychology, and communication. Forty-one states have continuing education requirements to renew a license. An audiologist must pass a separate exam to mold and place hearing aids. The American Board of Audiology and the American Speech-Language-Hearing Association (AHSA) offer professional certification programs for licensed audiologists.

Audiologists can go into private practice as a sole proprietor or as an associate or partner in a larger practice. They may also work in hospitals, outpatient clinics, and rehabilitation centers. Some are employed in state and local health departments and school districts. Some teach at universities and conduct academic research, and others work for medical device manufacturers. Audiologists may specialize in working with specific age groups, conducting hearing protection programs, or developing therapy programs for patients who are newly deaf or newly hearing.

Social Context and Future Prospects

According to the Bureau of Labor Statistics in there were 13,800 audiologists working in the United States in 2023. About 87 percent were employed in health care settings, 6 percent in educational settings, and 7 percent in specialized settings. The number of audiologists was expected to grow by sixteen percent between 2020 and 2030. The projected increased need can be traced to several factors.

As the population of older people continues to grow, so will the incidence of hearing loss from aging. In addition, the market demand for hearing aids is expected to increase as devices become less noticeable and existing wearers switch from analogue to digital models. At the same time, advances in medical treatment are increasing the survival rates of premature infants, trauma patients, and stroke patients, populations who may experience hearing loss.

Hearing aid manufacturers are on their fourth generation of productsdigital devices are becoming smaller and providing increasingly better sound processing. Neurosurgical techniques also are improving. Public health programs are promoting hearing protection. Excessive noise is the most common cause of hearing loss, and one-third of noise-related hearing loss is preventable with proper protective equipment and practices. Researchers are continuing to study the genes and proteins related to specialized structures of the inner ear. They hope to discover the biological mechanisms behind hearing loss in order to interrupt them or compensate for them on the molecular level.

As throughout the entire healthcare industry, artificial intelligence (AI) is touted as revolutionary in its coming ability to enhance audiology and hearing aids. Instead of serving as mere amplification devices, AI-enhanced hearing aids are projected to have the capability to combine signal processing and AI algorithms that improve the ability of devices to isolate desired sounds such as speech. Such devices will be able to distinguish noise in venues containing levels of competing noises and cacophonies. They will also allow for more personification of audio deciphering.

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