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Audiometry

Audiometry

Definition

Audiometry encompasses those procedures used to measure hearing thresholds.

Purpose

The purpose of audiometry is to establish an individual's range of hearing. It is most often performed when hearing loss is suspected. Audiometry can establish the extent as well as the type of a hearing loss. Audiometric techniques are also used when an individual has vertigo or dizziness , since many hearing and vestibular or balance problems are related. Since those with facial paralysis may also have hearing loss, audiologic testing may be performed on these individuals as well.

Description

The primary purpose of audiometry is to determine the frequency and intensity at which sounds can be heard. Humans can hear sounds in the frequency or pitch range of 20 to 20,000 Hertz (Hz), but most conversations occur between 300 and 3000 Hz. Audiometric testing is done between 125 and 8000 Hz. The intensity levels or degree of loudness at which sounds can be heard for most adults is between 0 and 20 decibels (dB).

Both air conduction and bone conduction of sounds are evaluated by audiometry. Air conduction establishes the extent of sound transmission through the bones of the middle ear. The results of a bone conduction test determine how soft a sound an individual can hear over several frequencies or pitches. Bone conduction audiometry determines the extent to which there is neurosensory hearing loss. An individual with a neurosensory loss may be able to hear sounds but not understand them. Since those with hearing losses often cannot hear sounds at normal decibel levels, intensities as high as 115 dB are used to assess the extent of air conduction loss and as high as 70 dB for bone conduction loss. The difference between bone conduction loss and neurosensory hearing loss is called the air-bone gap.

The most common method of assessing hearing ability is with the audiometer. Audiometric testing with the audiometer is performed while the patient sits in a soundproof booth and the examiner outside the booth communicates to the patient with a microphone. The patient wears headphones when air conduction is tested and a vibrating earpiece behind the ear next to the mastoid bone or along the forehead when bone conduction is tested. One ear is tested at a time, and a technique called masking, in which noise is presented to the ear not being tested, assures the examiner that only one ear is tested at a time. Through the headphones or earpiece pure sounds in both frequency and intensity are transmitted to the patient and the threshold at which the patient can hear for each frequency is established. The patient signals an ability to hear a sound by raising a hand or finger.

When the child is capable of understanding and responding to words, speech discrimination is also assessed as part of audiometry. Speech discrimination establishes one's ability to understand consonant sounds. In speech discrimination testing, two syllable words are read to and then repeated by the patient. This is an important part of audiometry, since much of a child's learning depends on the ability to discriminate speech. Older children of ten to 12 years of age have speech recognition comparable to adults and do well with speech discrimination testing. To insure that speech discrimination only is being assessed, this part of the hearing test is done at decibel levels of 30 to 40 decibels, higher than that of everyday conversation. By age five most children can do some type of speech discrimination testing.

Speech discrimination in the child of three to six years of age may be tested by having the child look at pictures of common objects as a monosyllabic word is read to him or her. The child indicates comprehension of the word by pointing to the corresponding object.

When evaluating infants, rather than testing of threshold levels, the examiner establishes the minimum response level at which the child responds to auditory stimuli. The minimum intensity level at which a neonate responds to sound is 25 dBs. This minimum level gradually decreases through infancy and at 36 months most children respond to sound intensities of less than 10 dBs.

For the young infant under four months of age, audiologists employ behavioral observation audiometry (BOA). The audiologist observes startle responses and motor reflex changes in the child as various noisemakers are employed to elicit these responses. The difficulty with this test is that the noises used are not standardized in frequency or intensity.

Visual reinforcement audiology (VRA) testing evaluates the hearing of infants from six months to two years. Sounds of varying intensity are presented to one of two speakers as the child sits on a parent's lap. If a sound is heard by the child, then he or she turns toward the appropriate speaker and is rewarded by a visual stimulus, such as an animated toy or a flashing light, although video images have been used for older children.

As the child gets older, condition play audiometry (CPA) is useful. The child is instructed to listen for a sound and to respond when a sound is heard by doing varying tasks, such as placing a ball in a cup or placing a peg in a pegboard, when the auditory stimulus is heard. Headphones may be worn by the child for this type of testing.

Because a reliable subjective response is difficult or impossible in a young patient electrophysiological testing is often performed. Electrophysiological testing is a reliable and nonbehavioral method to assess hearing loss in infants and young children and can be done while the child is either sleeping or under sedation. Some electrophysiological tests are the auditory brainstem response (ABR) test, auditory steady-state response (ASSR) testing, electroencephalic audiometry (EEG) test, and otoacoustic emission testing (OAE).

To perform the auditory brainstem response (ABR) test, headphones are placed on the infant or child and electrophysiological responses from the scalp and ears are recorded in response to tones sent through the headphones. A computer compiles the findings into a waveform that gives the examiner information about the location of a hearing problem anywhere along this pathway from the ear canal to the brainstem. This test is also called the brainstem auditory evoked response.

Auditory steady-state response (ASSR) testing also involves monitoring recorded responses from the scalp of tones at varying frequencies. This test is a more sensitive test than the ABR and can also measure residual hearing better. The EEG or electroencephalic audiometry test measures tone loss but cannot locate the site of a hearing loss. Otoacoustic emission testing (OAE) records spontaneous emissions from the ear and can detect middle ear problems. It is simpler than ABR, and it can be used to screen infants for severe hearing losses, since if hearing loss of greater than 40 dBs exist, no emission will be recorded.

An adjunct test of audiometry is acoustic immitance testing which assesses the facility with which sound can travel from the external ear to the cochlea inside the ear. The most familiar of this type of testing is the tympanogram, which determines if fluid has built up behind the eardrum.

Precautions

Audiometry is a safe procedure to which there are rarely contraindications.

Preparation

For most audiometric testing no special preparation is required, although the first time that hearing testing is done on a child the procedure should be explained as clearly as possible. If ABR or ASSR testing is done under sedation, then the child may not eat for several hours prior to administration of the drugs.

Aftercare

Audiometric testing, except when sedation is involved, requires no special aftercare.

Risks

If the ABR is used under sedation then the side effects of sedatives must be considered. Otherwise there are no risks associated with audiometry.

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.

Cochlear implantation A surgical procedure in which a small electronic device is placed under the skin behind the ear and is attached to a wire that stimulates the inner ear, allowing people who have hearing loss to hear useful sounds.

Decibel A unit of the intensity of sound or a measure of loudness. Normal speech is typically spoken in the range of about 2050 decibels.

Frequency Sound, whether traveling through air or the human body, produces vibrationsmolecules bouncing into each otheras the sound wave travels along. The frequency of a sound is the number of vibrations per second. Within the audible range, frequency means pitchthe higher the frequency, the higher a sound's pitch.

Parental concerns

Audiometry should be performed on all infants and children since unidentified hearing loss can delay speech and language skills. The earlier that a child with a hearing problem can be identified, the sooner the child's communication skills will develop. The audiometry available as of 2004 can determine the type and extent of a hearing loss as well as identify the location of the hearing problem. The results of audiometric testing can help determine if a hearing aid or cochlear implant may help a child. Audiometric testing can also be an adjunct to diagnosis of more serious problems related to hearing loss such a related syndrome or a tumor.

Parents of a child diagnosed with a hearing loss must be prepared to bring the child back for follow-up evaluations to monitor the hearing loss every three months for the first year after diagnosis and at least annually through the remainder of childhood. As the child gets older, more extensive audiometry testing can be performed.

Resources

BOOKS

Beasley, Donald J., and Ronald G. Amedee. "Hearing Loss." In Expert Guide to Otolaryngology, edited by Karen H. Calhoun. Philadelphia: American College of Physicians, 2001.

Miller, Andre J., and Gernard J. Gianoli. "Dizziness." In Expert Guide to Otolaryngology, edited by Karen H. Calhoun. Philadelphia: American College of Physicians, 2001.

Turkington, Carol, and Allen E. Sussman. Deafness and Hearing Disorders, 2nd ed. New York: Facts On File, 2004.

PERIODICALS

Firszt, Jill B., et al. "Auditory Sensitivity in Children Using the Auditory Steady-State Response." Archives of OtolaryngologyHead & Neck Surgery 130 (May 2004): 53640.

Schmida, Milton J., et al. "Visual Reinforcement Audiometry Using Digital Video Disc and Conventional Reinforcers." American Journal of Audiology 12, no. 1 (June 2003): 3540

Martha Reilly, OD

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"Audiometry." Gale Encyclopedia of Children's Health: Infancy through Adolescence. . Encyclopedia.com. 21 Aug. 2017 <http://www.encyclopedia.com>.

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"Audiometry." Gale Encyclopedia of Children's Health: Infancy through Adolescence. . Retrieved August 21, 2017 from Encyclopedia.com: http://www.encyclopedia.com/medicine/encyclopedias-almanacs-transcripts-and-maps/audiometry-0

Audiometry

Audiometry

Definition

Audiometry is the testing of a person's ability to hear various sound frequencies. The test is performed with the use of electronic equipment called an audiometer. This testing is usually administered by a trained technician called an audiologist.

Purpose

Audiometry testing is used to identify and diagnose hearing loss. The equipment is used in health screening programs, for example in grade schools, to detect hearing problems in children. It is also used in the doctor's office or hospital audiology department to diagnose hearing problems in children, adults, and the elderly. With correct diagnosis of a person's specific pattern of hearing impairment, the right type of therapy, which might include hearing aids, corrective surgery, or speech therapy, can be prescribed.

Precautions

Testing with audiometry equipment is simple and painless. No special precautions are required.

Description

A trained audiologist (a specialist in detecting hearing loss ) uses an audiometer to conduct audiometry testing. This equipment emits sounds or tones, like musical notes, at various frequencies, or pitches, and at differing volumes or levels of loudness. Testing is usually done in a soundproof testing room.

The person being tested wears a set of headphones that blocks out other distracting sounds and delivers a test tone to one ear at a time. At the sound of a tone, the patient holds up a hand or finger to indicate that the sound is detected. The audiologist lowers the volume and repeats the sound until the patient can no longer detect it. This process is repeated over a wide range of tones or frequencies from very deep, low sounds, like the lowest note played on a tuba, to very high sounds, like the pinging of a triangle. Each ear is tested separately. It is not unusual for levels of sensitivity to sound to differ from one ear to the other.

A second type of audiometry testing uses a headband rather than headphones. The headband is worn with small plastic rectangles that fit behind the ears to conduct sound through the bones of the skull. The patient being tested senses the tones that are transmitted as vibrations through the bones to the inner ear. As with the headphones, the tones are repeated at various frequencies and volumes.

The results of the audiometry test may be recorded on a grid or graph called an audiogram. This graph is generally set up with low frequencies or tones at one end and high ones at the other end, much like a piano keyboard. Low notes are graphed on the left and high notes on the right. The graph also charts the volume of the tones used; from soft, quiet sounds at the top of the chart to loud sounds at the bottom. Hearing is measured in units called decibels. Most of the sounds associated with normal speech patterns are generally spoken in the range of 20-50 decibels. An adult with normal hearing can detect tones between 0-20 decibels.

Speech audiometry is another type of testing that uses a series of simple recorded words spoken at various volumes into headphones worn by the patient being tested. The patient repeats each word back to the audiologist as it is heard. An adult with normal hearing will be able to recognize and repeat 90-100% of the words.

Preparation

The ears may be examined with an otoscope prior to audiometry testing to determine if there are any blockages in the ear canal due to ear wax or other material.

Normal results

A person with normal hearing will be able to recognize and respond to all of the tone frequencies administered at various volumes in both ears by the audiometry test. An adult with normal hearing can detect a range of low and high pitched sounds that are played as softly as between nearly 0-20 decibels. Normal speech is generally spoken in the range of 20-50 decibels.

Abnormal results

Audiometry test results are considered abnormal if there is a significant or unexplained difference between the levels of sound heard between the two ears, or if the person being tested is unable to hear in the normal range of frequencies and volume. The pattern of responses displayed on the audiogram can be used by the audiologist to identify if a significant hearing loss is present and if the patient might benefit from hearing aids or corrective surgery.

Resources

ORGANIZATIONS

American Academy of Audiology. 8201 Greensboro Drive, Suite 300, McLean, VA 22102. (703) 610-9022. http://audiology.org.

Audiology Awareness Campaign. 3008 Millwood Ave., Columbia, SC 29205. (800) 445-8629.

OTHER

"How to Read Your Hearing Test." Hearing Alliance of America. http://www.earinfo.com.

"Understanding Your Audiogram." The League for the Hard of Hearing. http://www.lhh.org.

KEY TERMS

Audiogram A chart or graph of the results of a hearing test conducted with audiographic equipment. The chart reflects the softest (lowest volume) sounds that can be heard at various frequencies or pitches.

Decibel A unit of measure for expressing the loudness of a sound. Normal speech is typically spoken in the range of about 20-50 decibels.

Otoscope A hand-held instrument with a tiny light and a funnel-shaped attachment called an ear speculum, which is used to examine the ear canal and eardrum.

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Audiometer

Audiometer

An audiometer is an instrument used to measure how well a person hears. The ear is a complex organ. It receives sound in the form of vibrations that strike the eardrum. These vibrations move from the eardrum through the bones of the middle ear to the cochlea (a spiral-shaped organ filled with fluid). The vibration sets the fluid in motion and sensory cells along the cochlea's basilar (at the bottom or base of) membrane (a thin covering through which things can pass) send messages of the sound to the brain.

The brain distinguishes many distinct sounds. Pitch music. Sounds of over 140 decibels, such as those made by a jet aircraft, can damage hearing.

The Audiometer Test

An audiometer consists of four parts. These parts are the oscillator (used to change the frequency of sounds heard), an audio amplifier, an attenuator (used to control volume loudness), and a pair of headphones. The person being tested wears the headphones. The amplitude of a tone is slowly increased until the person hears the sound. The lowest decibel level at which a sound is heard is called the threshold. The oscillator is used to change pitch so a range of sounds can be tested. When manufacturing audiometers and performing audiometer testing, care is taken to eliminate background noise.

The result of a hearing test using an audiometer is called an audiogram. The audiogram is a graph that shows the lowest decibel level at which each frequency is heard. The graph gives a profile of the person's threshold of hearing. It compares the profile to a line representing normal hearing in order to detect hearing loss. Using the audiometer, frequency is varied from 64 hertz to over 8,000 hertz. Amplitude can be varied in five decibel increments. In addition to pure tones, speech sounds are sometimes used as test signals. Hearing is considered good if every tone sounded between 64 and 8,192 hertz is heard at a volume of 20 decibels. Hearing loss is generally greatest at the high frequencies. This seems to occur in many people over fifty.

Békésy's Invention

The pure-tone audiometer was invented by Georg von Békésy (1899-1972; winner of the Nobel Prize), a Hungarian-American physicist. His machine was a patient-operated instrument released in 1946. Békésy studied the transmission of sound for a Hungarian telephone company. The testing the telephone lines was routinely carried out and often done with pure tones (tones of one frequency). Bekesy listened to everything he heard over the telephone lineshe even listened to the clicks when phones were being connected and disconnected! He started using the clicks as test signals. The clicks themselves were a combination of many pure tones that came along the telephone lines in a single short pulse. Bekesy's early experiences helped him study hearing in great detail and arrive at his audiometer design.

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audiometry

au·di·om·e·try / ˌôdēˈämitrē/ • n. measurement of the range and sensitivity of a person's sense of hearing. DERIVATIVES: au·di·om·e·ter / -itər/ n. au·di·o·met·ric / -əˈmetrik/ adj.

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electrocochleography

electrocochleography (ECoG) (i-lek-troh-kok-li-og-răfi) n. a test to measure electrical activity produced within the cochlea in response to a sound stimulus. It is used in the diagnosis of Ménière's disease and other forms of sensorineural deafness.

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audiometer

audiometer (awdi-om-it-er) n. an apparatus for testing hearing at different sound frequencies, so helping in the diagnosis of deafness.
audiometry n.

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audiometer

audiometer An instrument that generates a sound of known frequency and intensity in order to measure an individual's hearing ability.

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audiogram

audiogram (aw-di-oh-gram) n. the graphic record of a test of hearing carried out on an audiometer.

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