Brain Stem Electric Response Audiometry: A Clinical and Theoretical Analysis, including and Experimental Study of the Effect of Ear Canal Collapse on BERA Testing
Harrington, Mary E.
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Over the past decade the technique of Brain Stem Electric Response Audiometry (BERA) has grown to assume a prominent position in the fields of Audiology and Otolaryngology. Its role in both of these fields is seen by examining the two major functions of the test. The primary function of BERA is to evaluate the operability of the auditory nerve in the brain stem. This particular nerve, the eighth nerve or "hearing" nerve, carries information from the inner ear to the brain. Any obstruction in the pathway from the auditory nerve to the brain can cause problems for the patient. Such problems include ringing in the ears, equilibrium distortion, hearing loss and pain in the head region. These problems may result from: a build-up, such as a tumor or blood clot, on the auditory nerve, from the presence of diminished brain stem circulation, or from demyelinization of the brain stem. It is very important that the cause of these problems be identified quickly as a rapid diagnosis will diminish the side effects of correction procedures. BERA serves as an objective diagnostic tool allowing for speedier detection of auditory nerve damage with virtually no discomfort for the patient. In this way it serves as a valuable tool for the otolaryngologist (ear, nose and throat physician). The secondary function of BERA testing is to evaluate a patient's auditory threshold (lowest level at which the patient responds to auditory stimuli). In the past, brain stem audiometry has been limited in its ability to assess a patient's auditory threshold. The mechanics of the technique limit the test region to the higher frequencies (basal region of the cochlea). BERA is functional in measuring a patient's threshold in the higher frequencies. Unfortunately, when testing neonates (infants) and young children it is necessary to know the functioning of the lower frequency (apical) regions of the cochlea as well. Numerous studies have attempted to include low frequency stimuli in BERA techniques. Though these studies have led to successful advancements in the area of low frequency testing, the results have not been consistent enough or reliable enough for benefit in the clinical setting. Enhancing the response characteristics of low frequency stimuli in BERA testing would provide a further diagnostic tool for the clinical audiologist. The purpose of this project is to present an overview of Brain Stem Electric Response Audiometry. with an emphasis on its clinical advantages. and then to focus on a related experiment designed to enhance the diagnostic functions of the test. The latter experiment will be treated as an individual unit within the context of brain stem audiometry.