Index
It covers the procedures used to measure hearing thresholds.
Purpose
The goal of audiometry is to establish an individual’s hearing range. Generally, it is done when hearing loss is suspected.
Audiometry can establish the extent and hearing loss. Audiometric techniques are also used when a person has vertigo or dizziness since many hearing and vestibular or balance problems are related.
Since people with facial paralysis can also have hearing loss, audiological tests can also be done on these people.
Description
The primary purpose of audiometry is to determine the frequency and intensity with which sounds are heard.
Humans can hear sounds in the 20 to 20,000 Hertz (Hz) frequency or pitch range, but most conversations occur between 300 and 3000 Hz. The audiometric test is performed between 125 and 8000 Hz.
Intensity levels, or the degree of intensity with which sounds are heard for most adults, are between 0 and 20 decibels (dB).
Both air conduction and bone conduction of sounds are assessed 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 the sound is that an individual can hear at various frequencies or pitches. Bone conduction audiometry determines the degree of sensorineural hearing loss.
An individual with sensorineural loss may hear sounds but not understand them.
Since people with hearing loss often cannot hear sounds at normal decibel levels, intensities as high as 115 dB are used to assess the degree of air conduction loss and as high as 70 dB for bone conduction loss.
The difference between bone conduction loss and sensorineural hearing loss is the air-bone gap.
The most common method of assessing hearing ability is with the audiometer.
The audiometric test with the audiometer is performed while the patient sits in a soundproof booth and the examiner outside the booth communicates with the patient with a microphone.
The patient wears hearing aids when testing air conduction and a vibrating hearing aid behind the ear next to the mastoid bone or across the forehead when testing bone conduction.
One ear is tested at a time, and a technique called masking, in which noise is presented in the ear that is not being tested, assures the examiner that only one ear is tested at a time.
Through headphones or earphones, pure sounds in 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 the ability to listen to a sound by raising a hand or finger.
Speech discrimination is also assessed as part of audiometry when the child can understand and respond to words.
Speech discrimination establishes one’s ability to understand consonant sounds. In speech discrimination tests, the patient reads and repeats two-syllable words.
This is an essential part of audiometry, as much of a child’s learning depends on the ability to discriminate speech.
Children older than 10 to 12 years of age have speech recognition comparable to adults and do well with speech discrimination tests.
To ensure that speech discrimination is only being assessed, this part of the listening test is performed at decibel levels of 30 to 40 decibels, higher than those of daily conversation.
By the age of five, most children can take some speech discrimination test.
Speech discrimination in the 3- to a 6-year-old child can be tested by having the child look at pictures of everyday objects as a monosyllabic word is read to him. The child indicates the understanding of the word by pointing to the corresponding object.
In evaluating infants, the examiner establishes the minimum response level at which the infant responds to auditory stimuli rather than testing threshold levels.
The minimum intensity level at which a newborn responds to sound is 25 dB. This minimum level gradually decreases during infancy, and by 36 months, most children respond to sound intensities below 10 dB.
Audiologists use behavioral observation audiometry (BOA) for babies younger than four months old.
The audiologist observes the child’s startle responses and changes in motor reflexes, as various noise factors are used to elicit these responses.
The difficulty with this test is that the noises used are not standardized in frequency or intensity.
Visual reinforcement audiology tests (VRAs) evaluate babies’ hearing from six months to two years. Sounds of varying intensity are presented to one of the two speakers while the child sits on the lap of one of the parents.
If the child hears a sound, they turn to the appropriate speaker and are rewarded by a visual stimulus, such as an animated toy or flashing light. However, video images have been used for older children.
As the child grows, play condition audiometry is helpful. The child is instructed to listen to a sound and respond when a sound is heard by doing variable tasks, such as placing a ball in a cup or placing a peg on a board, when the auditory stimulus is heard.
The child can use headphones for this type of test.
Electrophysiological testing is often performed because a reliable subjective response is difficult or impossible in a young patient.
Electrophysiological testing is a reliable, non-behavioral method of evaluating hearing loss in infants and young children and can be performed while the child is sleeping or under sedation.
The tests are:
- The Auditory Brainstem Response (ABR) test.
- The Auditory Steady-State Response (ASSR) test.
- The Electro-brain Audiometry (EEG) test.
And Otoacoustic Emission (OAE) tests.
To perform the Auditory Brainstem Response (ABR) test, headphones are placed on the infant or child. The electrophysiological responses of 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 an auditory brainstem evoked response.
The Auditory Steady-State Response Test (ASSR) also involves monitoring responses recorded from the scalp to tones at varying frequencies.
This test is more sensitive than ABR and can better measure residual hearing. The EEG or electro-brain audiometry test measures the loss of tone but cannot locate the site of a hearing loss.
An otoacoustic emission (OAE) test records spontaneous ear emissions and can detect middle ear problems.
It is simpler than ABR and can be used to detect severe hearing loss in children since if there is a hearing loss greater than 40 dB, no emission will be recorded.
An adjunct audiometry test is the acoustic immunity test that evaluates the facility with which sound can travel from the outer ear to the cochlea within the ear.
The most familiar of this type of test is the tympanogram, which determines whether fluid has collected behind the eardrum.
Precautions
Audiometry is a safe procedure for which there are rarely contraindications.
Preparation
No special preparation is required for most audiometric tests, although the first time a hearing test is performed on a child, the procedure should be explained as clearly as possible.
If the ABR or ASSR test is performed under sedation, then the child is unable to eat for several hours before administration of the medications.
Aftercare
Audiometric tests, except for sedation, do not require special aftercare.
Risks
If ABR is used under sedation, the side effects of sedatives should be considered. Otherwise, there are no risks associated with audiometry.
Key terms
Audiologist – A person with a degree and certification in hearing impairment identification and measurement and the rehabilitation of the hearing impaired.
Cochlear implant: A surgical procedure in which a small electronic device is placed under the skin behind the ear and connected to a wire that stimulates the inner ear, allowing people with hearing loss to hear valuable sounds.
Decibel: a unit of sound intensity or a measure of loudness. Everyday speech is typically spoken in about 20-50 decibels.
Frequency: Sound, whether through the air or the human body, produces vibrations, molecules that combine as the sound wave advances.
The frequency of a sound is the number of vibrations per second. Within the audible range, frequency means pitch: the higher the frequency, the higher the pitch of the sound.
Parental concerns
Audiometry should be performed on all infants and children as unidentified hearing loss can delay speech and language skills.
The sooner a child with a hearing problem can be identified, the sooner the child’s communication skills will develop.
Audiometry available as of 2004 can determine the type and extent of a hearing loss and identify the location of the hearing problem.
Audiometric test results can help determine if a hearing aid or cochlear implant can help your child.
Audiometric tests can also be an adjunct to diagnosing more severe problems related to hearing loss, such as a related syndrome or tumor.
Parents of a child diagnosed with hearing loss should be prepared to take the child for follow-up evaluations to monitor hearing loss every three months for the first year after diagnosis and at least annually for the remainder of childhood.
