An ABR (Auditory Brainstem Response test) is not a hearing test, but rather a test of auditory function above the level of the ear (from the auditory nerve through the brain stem to higher brain regions). When sound enters the ear and stimulates the cochlea in the inner ear, the cochlea produces an electrical response to the sound along the nerve pathways. This electrical response is the same type of response that is measured in an Electroencephalogram (EEG), a study of brain waves that may be more familiar to you. ABR waveforms (the electrical “waves” of nerve/brain activity in response to sound) can be measured on your skin using measurement electrodes. The responses can be interpreted to yield valuable information about the function of the auditory pathways. In analyzing the ABR, the audiologist and physician look at the presence of the various waveforms, at how long it takes each wave to occur, the distance between certain waves and the shape and height of the waves. The waves or responses of the two ears are compared to each other to further aid diagnosis.
Most commonly, the test is used to verify normal function of auditory pathways. ABRs are often ordered by your physician when there is greater loss of hearing in one ear or if you have complaints of dizziness or tinnitus (ringing). It can also be used to help determine the degree of hearing loss in infants, young children and other patients who are otherwise unable to provide reliable responses through traditional behavioral hearing tests or when additional confirmation of behavioral test results is needed. The ABR requires no active participation on the part of the patient and can provide reliable information whether the patient is awake or asleep.
We sometimes refer to the ABR as the “La-Z-Boy Test” because during the test the patient sits in a comfortable recliner and is instructed to just sit back, relax, and go to sleep if desired while the lights are turned down low. Prior to starting the test, one of our ACENTA audiologists will clean your skin on the forehead area and in the outermost part of your ear canals with gauze or a cotton swab. Electrodes are then applied to your forehead and earphone-electrodes (like little earplugs) are inserted in each ear. The ear canal electrode doubles as an earphone, producing a clicking sound once the test begins. A fairly loud clicking sound is presented to each ear. Muscle tension and muscle movement can interfere with measurement and cause the test to be prolonged or even decrease its accuracy. Patients are therefore encouraged to relax, especially in the jaw, face and neck. Sleeping is fine as long as the patient does not begin to snore. This test is quick and painless and for many people it is a fairly relaxing experience. The test lasts approximately 30 minutes when patients are fully relaxed and still.
ABR testing for infants often takes more time than when testing adults. Infants are required be asleep during testing since they are not capable of relaxing and lying motionless. Sometimes young infants are able to sleep naturally during the test, but other infants require a mild oral sedative such as chloral hydrate. This prescription is ordered by your physician and is based upon the weight of your child. Chloral hydrate is typically administered by ACENTA’s nurse and your child’s breathing and pulse are monitored throughout the test. Parents should ensure that their child is somewhat sleep deprived and should prevent the child from napping prior to the test to increase the likelihood that the child will sleep throughout the test. Testing time depends upon how quickly your child goes to sleep, but most tests are scheduled for an hour-and-a-half. Parents are also encouraged to bring a bottle or sippy cup to the appointment as well as a pacifier when appropriate. Feel free to let your child wear pajamas or other warm, cozy clothes and do not hesitate to bring a blanket and favorite stuffed animal or quiet toy that relaxes the child.