Electrophysiological Evaluations including Auditory Brainstem Response and Otoacoustic Emissions
Auditory Brainstem Response (ABR) is a measurement used on hard to test patients. It can also be used diagnostically to locate lesions along the auditory nerve and help the physician diagnose auditory pathologies. Commonly, an ABR will be obtained if an infant did not pass their newborn hearing screening and follow-up testing in one or both ears. This test is the most reliable way to determine the quietest sounds (threshold) the infant can hear.
While the infant is sleeping little electrodes are placed on their head and earphones cover their ears. For example, a normal hearing infant will hear the sound (clicks) which will stimulate the cochlea, which will then stimulate the brain. The electrode picks up on the stimulation from the brain and traces it on a computer in the form of a wave. If the waves are still there, even when the sounds get quiet, it can be assumed that the infant has normal hearing. If the infant has a hearing loss, then the Audiologist will raise the level of the clicks until the waves can be seen.
Distortion Product Otoacoustic Emissions (DPOAEs) is a measurement that is used on hard-to-test patients. This test is currently the preferred test used to test newborns. It is also used as part of test battery for differential diagnosis in adults. The test is conducted by inserting a small rubber probe into the patient’s ear. The test will produce two distorted sounds which stimulate certain hair cells in the cochlea. Once the hair cells are stimulated, if they are healthy, they will send back an echo sound which is picked up by a sensitive microphone in the probe. DPOAEs are used as a test of inner ear function and are not a measure of hearing.