While hearing loss can be a normal part of the aging process, exposure to excess noise can threaten hearing in the young.
President Ronald Reagan experienced a significant loss of hearing while in the White House. Before leaving the presidency in 1989, Reagan began wearing a hearing aid to improve his perception of sound. His physicians did not consider the hearing loss unusual, considering the president’s age. (Ronald Reagan became president at the age of 69 and left office at age 77.) The hearing loss experienced by Mark Herndon, drummer for the popular country band Alabama, however, was unexpected. Herndon was only 27 when he discovered that he had lost hearing in higher frequencies. Physicians diagnosed the loss as the result of years of performing in front of stacks of blasting speakers. Herndon now wears earphones or earmuffs on stage to protect his hearing.
More than 28 million people in the United States—nearly 10 percent of the population in 1999—have experienced hearing loss to some degree, according to the Better Hearing Institute, a nonprofit, educational organization based in Washington, D.C. Traditionally, the elderly make up the largest percentage of those 28 million people. In 1998, age-related hearing loss affected 30 to 35 percent of the population between the ages of 65 to 75 years and 40 percent over age 75. However, in the 1990’s, researchers discovered a sharp increase in hearing loss among younger people. The Better Hearing Institute reported in 1998 that as much as 10 percent of the U.S. population aged 40 to 65 had experienced some degree of hearing loss. Loud music blasting from stereos and radio boomboxes, sound effects blaring from video games, booming sound systems in movie theaters, and the high-intensity sounds of everyday life can cause almost anyone to lose some of his or her hearing over time.
Types of hearing loss
Physicians categorize most hearing losses as either sensorineural, conductive, or “mixed.” Approximately 95 percent of all hearing loss in the United States is classified as sensorineural, according to the Better Hearing Institute. This type of hearing loss is produced by damage to the structures of the inner ear. The structures include the cochlea (the organ in the inner ear that transforms sound to electric nerve impulses) and the sensory hair cells and nerve fibers that transmit nerve impulses to the brain. Inner ear damage is most commonly the result of aging or prolonged exposure to loud noises. Age-related hearing loss is called presbycusis, a condition in which the sensory hair cells in the inner ear die.
Traumatic head injuries and sharp blows to the ear can also result in sensorineural hearing loss. Damage to the inner ear can be triggered by certain diseases and medical conditions, including viral infections, such as mumps or measles; Meniere’s disease, which increases fluid pressure in the inner ear; bacterial meningitis, a brain infection that can damage the acoustic nerve; and acoustic neuroma, a benign brain tumor. Certain antibiotics, such as streptomycin, gentamicin, and neomycin, can result in sensorineural hearing loss. Aspirin, if taken in large quantities, also can cause hearing loss. The condition is also associated with certain birth defects and inherited inner ear abnormalities.
Conductive hearing loss is produced by sound blockage between the outer and inner ear. Sound travels in waves from the outer ear through the ear canal to the eardrum, a thin membrane of tissue that vibrates when hit by sound. Vibrations travel from the eardrum through the middle ear. The middle ear contains tiny bones that pass the vibrations to the inner-ear membrane. In the inner ear, the vibrations are converted to electric impulses that are transmitted to the brain through the acoustic nerve.
A number of medical conditions produce conductive hearing loss. The most common, especially among children, is otitis media. This inflammation of the middle ear is most often caused by colds or other upper respiratory tract infections. Sticky fluids build up behind the eardrum, which can become infected.
Otosclerosis is another disorder that causes progressive conductive hearing loss. The condition, which is usually inherited and occurs for unknown reasons, produces an overgrowth of bone in the middle ear that eventually immobilizes the stapes (the innermost bone of the middle ear). Sound cannot pass to the inner ear if the stapes is unable to vibrate. A perforated eardrum, tumors, changes in air pressure, and a foreign body in the middle ear, such as a wax blockage, are also common causes of conductive hearing loss.
Mixed hearing loss is a combination of the sensorineural and conductive types of hearing loss. It can result from infections, tumors, genetic disorders, and head and ear injuries. A middle ear infection can damage the eardrum and the tiny bones that conduct sound waves and then move into the inner ear. Certain tumors can block the flow of sound waves in the ear canal or middle ear and then spread to the inner ear.
Preventing hearing loss
Some forms of hearing loss cannot be prevented, and noise, the most common cause of hearing loss after aging, is also the most easily preventable. Most experts agree that hearing loss among people 40 to 65 years old is generally the result of exposure to excessive levels of noise. The National Institute on Deafness and Commun-ication Disorders (NIDCD), a privately-funded, research foundation located in Washington, D.C., reported in 1998 that as many as 20 million Americans were exposed annually to hazardous levels of noise or worked in dangerously noisy environments.
Research in the late 1990’s also revealed that noise-induced hearing loss was affecting the nation’s school-age population. The Centers for Disease Control and Prevention (CDC), located in Atlanta, Georgia, reported in 1998 that hearing loss among school-age children has become widespread in the United States. In 1998, 15 percent of all children between the ages of 6 and 19 had experienced hearing loss to some degree. A significant proportion of incidences resulted from avoidable noise, such as prolonged loud music and video games.
Noise is measured in decibels. The higher the decibel level, the greater the effect on hearing. A whisper registers at 30 decibels (db). Normal conversation ranges from 50 to 65 db. A hairdryer or vacuum cleaner produces 70 db. None of these sounds damage hearing.
Damage occurs after prolonged exposure to sounds at 80 db or higher. City traffic can hit 80 db. Noise from lawnmowers ranges from 85 to 90 db. Subway and motorcycle sounds reach 90 db. Stereo volume set at the half-way mark registers 100 db. Rock concerts often hit 110 db. A jet taking off produces 120 db, a radio “boombox” can reach 120 db, a jackhammer 130 db, and a shotgun 140 db. The higher the decibel level, the less exposure time it takes to damage human hearing.
Physical effects of excessive noise levels
Prolonged exposure to noise at hazardous levels eventually injures the sensory hair cells in the inner ear. This injury causes swelling of the nerve endings in the cochlea, particularly at the base, where the nerve endings are extremely sensitive to high-intensity sound.
Excessive noise levels initially produce a short-term hearing loss, known as a temporary threshold shift. Sounds are muffled, usually for a few hours or a day. People who attend a rock concert, for example, often experience temporary threshold shift. They hear ringing or buzzing sounds and feel a sense of fullness in their ears. Normal hearing returns after damaged hair cells repair themselves, which usually begins the first day after exposure to the noise.
Hair-cell repair, however, can take as long as a month, depending on the damage done and an individual’s sensitivity to noise. If exposure to loud noises is constant or frequent, inner ear hair cells may lose the ability to bounce back. They die, producing irreversible hearing loss.
A second type of noise-induced hearing loss is acoustic trauma, which is produced by a single exposure to a noise of very high intensity, such as an explosion. Such a sound can rupture the ear-drum and blow apart the structures of the inner ear. A person who is experiencing acoustic trauma may become dizzy, feel pain, and hear ringing in the ear. The ear closest to the explosion usually suffers more damage than the opposite ear. A person suffering hearing loss due to acoustic trauma may regain some or all of his or her hearing over time.
Recognizing hearing loss
How do people know they are losing their hearing? There are a number of warning signs. The first sign may be asking other people to repeat what they are saying or missing parts of conversations, especially when there is a lot of background noise, such as at a restaurant or party.
Other warning signs of possible hearing loss include being unable to hear over the telephone; finding oneself unable to follow a conversation involving two or more people; turning the TV or radio volume higher in order to hear it; being unable to determine where sounds are coming from; deciding that other people are not speaking clearly; responding incorrectly to a misunderstood question; or not hearing ringing of doorbells or telephones.
Babies born with impaired hearing may fail to turn their head or move their eyes in response to voices or other sounds. An infant with impaired hearing may not form sounds or words at the right time and may have difficulty learning to speak. A child with hearing loss may have trouble carrying on a conversation or may constantly turn one ear to hear a voice or other sounds.
Individuals who experience hearing loss may withdraw socially and experience confusion, depression, and feelings of inadequacy. They often deny or attempt to cover their loss. They may also exhibit embarrassment, frustration, impatience, and guilt.
Diagnosing a loss of hearing
While sensorineural and conductive hearing loss can be permanent, proper treatment helps many people with hearing loss improve their hearing. The first step is to see a physician. A family physician, in turn, may refer a patient with hearing problems to an audiologist (a specialist trained to evaluate hearing problems) or to an otolaryngologist (ear, nose, and throat doctor) or otologist (another ear specialist) to determine the kind of hearing loss.
During a hearing test, the audiologist seats a patient in a soundproof booth and places a set of headphones over his or her ears. The audiologist broadcasts various tones and various noise levels through the headphones. An audiometer, a machine that measures the intensity of sounds, plots test results on an audiogram, a sheet on which hearing impairment is classified on a scale from mild to profound.
A person with normal hearing can pick up sounds that range between 0 to 20 db. A person who is unable to hear sounds below 20 to 45 db is classified as having suffered a minor hearing loss. Moderate loss involves sounds between 45 and 60 db and moderately severe, between 60 and 75 db. Individuals with severe hearing loss are unable to hear sounds ranging from 75 to 90 db, and people with profound hearing loss do not hear sounds as loud as 90 db and above. With the audiogram results and other tests, the audiologist determines the degree of hearing loss and recommends appropriate treatment.
Treating hearing loss
Treatment for hearing loss can range from the removal of earwax to corrective surgery. Physicians use a syringe and warm water to remove a build-up of earwax, which can cause temporary conductive hearing loss. When otitis media causes conductive hearing loss, resulting in a collection of sticky fluid in the middle ear, the individual may need an operation to drain the fluid through a hole created in the eardrum. If there is no build-up of fluid, antibiotics may be given to clear the infection.
Surgical procedures for hearing loss include tympanoplasty, to repair perforated eardrums, and stapedectomy, to remove a bone damaged by otosclerosis and replace it with an artificial bone. Physicians also recommend hearing aids in some cases of otosclerosis.
Hearing aids are battery-operated electronic instruments that collect sound waves, amplify them electronically, and aim the sound into the ear. They are most often used to treat sensorineural hearing loss. They do not cure the loss but increase the volume of the sound that reaches the inner ear. The components of most hearing aids include an amplifier, receiver, microphone, earpiece, and batteries.
There are essentially three types of hearing aids available—the behind-the-ear type; in the ear; and in the canal. The behind-the-ear type has an amplification device with a microphone that fits in back of the ear. Amplified sound travels through a flexible plastic tube to a small plastic earmold in the ear itself. Behind-the-ear hearing aids can also be mounted on eyeglasses.
The in-the-ear type of hearing aid is the most commonly used type. This hearing aid has an amplifier, microphone, and speaker contained in a shell-shaped container that is custom fitted to the shape of an individual’s ear. It sits on the opening to the ear canal.
The in-the-canal style of hearing aid, which fits down in the lower portion of the ear canal, is considerably smaller and less powerful than the in-the-ear style. One type of in-the-canal device can be placed deeply in the ear canal. Only a tiny portion of it shows at the opening to the ear canal. The in-the-canal styles are popular because they are the least visible of all external hearing aids.
Hearing aids are equipped with a variety of electric circuitry. The majority of hearing aids are made with analog circuits, which is the same technology used to transmit television signals. When sound waves enter analog hearing aids, they are amplified across the entire spectrum of sound.
Hearing aids are also made with digital circuits, which convert incoming sound to binary numbers that are processed by a computer chip. Digital devices separate background noise from speech, eliminating some of the noise distortion that may accompany analog units.
A third type of hearing-aid circuit is a programmable or combined digital/analog circuit. They are programmed with digital circuits to adapt to a wide range of hearing loss but amplify the sound using analog circuitry. The duel technology allows the user to change settings in order to adjust to various environments.
A cochlear implant, which can be helpful to people with profound sensorineural hearing loss, is an electronic device that is surgically implanted into the inner ear. Cochlear implants compensate for the missing function of dead sensory hair cells in the inner ear. The implant consists of a small external microphone, worn behind the ear, that picks up sound. The sound travels through a wire to a speech or signal processor that converts speech into digital signals.
The best way for an individual to improve his or her hearing, however, is to avoid situations that may inflict damage. Not all types of hearing loss can be prevented, but with a little caution, the individual can help preserve his or her hearing for a long time.