Audiology > Audiology & Vestibular tests
Auditory brainstem response testing uses computer equipment to record the auditory nerve’s response to sounds delivered to the ears via headphones. The response is recorded from recording disks placed on the patient’s head. This testing is used primarily to diagnose hearing loss in infants and very young children who can’t reliably respond to testing or in adults for site-of-lesion testing.
Auditory brainstem response testing is also used to determine the function of the auditory nerve in adults. This type of testing is often called site-of-lesion testing, and is similar to the auditory brainstem response testing of infants and young children.
An electronystagmogram (VNG) measures normal eye movement and involuntary rapid eye movements called nystagmus. It also checks the muscles that control eye movements. ENG checks how well the eyes, inner ears, and brain help you keep your balance and position (such as when you change from lying down to standing).
There is an interaction between the eyes, eye muscles and the inner ear balance system. During an electronystagmography or ENG test, eye movements are recorded by electrodes placed around the eyes or by special video cameras fitted on goggles placed over the eyes. A computer analyzes the eye movements and provides information about the kind of messages the inner ear is sending to control the movement of the eyes through the central nervous system. This is currently the best way to check how well the inner ear balance mechanism works.
During the first part of the test, the patient stares at a spot or a light. Next, they watch a light moving on a bar. The third part of the test records eye movements as the patient lies on a bed in different positions (lying on right side, left side, etc.). During the final portion of the test, warm and/or cool water or air will be placed in the outer ear canals.
Why It Is Done
An electronystagmogram (VNG) is done to:
• Find where the problem is in the inner ear, brain, or nerves connecting them that is causing dizziness, vertigo, or a loss of balance.
• Find any damage to structures or nerves in the inner ear, brain, or nerves connecting them.
An audiogram is graphical representation of a hearing test that is generally performed in a sound suite using sophisticated, calibrated equipment. A certified audiologist administers the test. Headphones are placed over or in the person's ears, and tones are presented to each ear, one at a time. The softest level at which the sounds can be heard is recorded as the threshold of hearing.
ECOG is a variant of brainstem auditory evoked response (BAER) where the recording electrode is placed on the tympanic membrane (ear drum). It is intended to diagnose Meniere's disease, and particular, hydrops (swelling of the inner ear). ECOG may also be abnormal in perilymph fistula and in sudden hearing loss. The cochlear microphonic of ECOG may be normal in auditory neuropathy as well as other disorders in which the cochlea is preserved but the auditory nerve is damaged. ECOG's have also been used to as a indicator of the temporary threshold shift that may follow noise injury.
The technique involves placing the electrode on the tympanic membrane, a location across the middle ear from the cochlea. The ear is stimulated with alternating polarity clicks (although tone bursts can also be used). The objective is to record wave-1 (there are 5 waves), with greater accuracy and to detect the "summating potential", which is a shoulder on wave 1. In some instances, the cochlear microphonic is inspected. A person with an intact cochlear microphonic but reduced or absent wave 1, might have a 8th nerve site of lesion. In other words, the sound gets to the cochlea (creating the microphonic), but doesn't make it into the brainstem (i.e. no waves 1-5)
ECOG results are reported as an SP/AP ratio, for which a ratio of 0.5 or greater is considered abnormal. While some labs use 0.35 instead, The sensitivity of the SP/AP ratio to Meniere's disease 60-71%. The sensitivity is said to be higher if it is performed during a symptomatic period), but it is difficult to get patients scheduled for the test when they are symptomatic. Also, some authors disagree that sensitivity is increased when patients are symptomatic.
Both hearing and balance occur within the ear.
In hearing, sound waves pass from the outer ear into the auditory canal. They strike the eardrum, making it vibrate.
These vibrations travel to the middle ear, setting into motion three tiny bones: the hammer, anvil, and stirrup.
The vibrations continue through the cochlea and deep into the inner ear, which contain a fluid reservoir.
As fluid ripples across membranes, it stirs tiny hairs connected to nerve endings. The stimulated nerve endings carry impulses into the brain where they are interpreted as sound.
Also located in the inner ear is the equilibrium, or balance center. The center sends continuous messages about the body's position to the brain. This information helps us maintain balance.
The primary purpose of otoacoustic emission (OAE) tests is to determine cochlear status, specifically hair cell function. This information can be used to (1) screen hearing (particularly in neonates, infants, or individuals with developmental disabilities), (2) partially estimate hearing sensitivity within a limited range, (3) differentiate between the sensory and neural components of sensorineural hearing loss, and (4) test for functional (feigned) hearing loss. The information can be obtained from patients who are sleeping or even comatose because no behavioral response is required.
The normal cochlea does not just receive sound; it also produces low-intensity sounds called OAEs. These sounds are produced specifically by the cochlea and, most probably, by the cochlear outer hair cells as they expand and contract. The presence of cochlear emissions was hypothesized in the 1940s on the basis of mathematical models of cochlear nonlinearity. However, OAEs could not be measured until the late 1970s, when technology created the extremely sensitive low-noise microphones needed to record these responses.
The 4 types of otoacoustic emissions are as follows:
Tympanometry
Tympanometry is a test where air pressure in the ear canal is varied to test the condition and mobility (movement) of the ear drum (tympanic membrane) and is useful in detecting disorders of the middle ear.
Tympanometry determines the functionality of the tympanic membrane by observing its response to waves of pressure, and measuring the air pressure of the middle ear.
The normal air pressure inside the middle ear is 100 (a very small amount). The tympanic membrane motion should appear smooth and symmetrical.
Abnormal Tympanometry results may be indicative of any of the following:
The test is initiated by performing a visual inspection of the external auditory canal of the patient with an otoscope to evaluate the ear canal of the patient and to ensure that there is a clear path to the ear drum. A probe tip then is inserted into the ear of the individual that will change the air pressure in the patient’s ear, produce a pure tone, and measure the body's responses to the sound and different pressures.
During the test, it is important for the patient not to speak, move, swallow, or startle. All these actions can alter the pressure in the middle ear and invalidate the test results. The sounds heard during the test may be loud and potentially startling, so a conscious effort of the patient is required to avoid a startle reflex.