Bera test or Bera test for hearing or Brainstem evoked potentials or Brainstem evoked response Audiometry or abr hearing restore ABR hearing restore auditory brainstem response or auditory brainstem response interpretation or auditory brainstem response pathway or auditory brainstem response waves or auditory neuropathy or auditory neuropathy spectrum disorder or abr test for hearing
BERA test is an objective test of hearing. Auditory brainstem responses (ABR) were initially described in 1971 by Jewett and Wilson. he described it to be a fascinating study of the neurological transmission of an auditory stimulus from the ear to the brain. When electrodes are placed over the scalp and auditory stimulus is given, seven waveforms are recorded which happens sequentially in a certain time frame and these seven waveforms represent auditory brainstem responses. Seven waves represent a particular area of the hindbrain. For a few waves, certain areas are not very clearly defined. so, to keep it simple we will just name the probable sites. so, Wave I come from the distal portion of the eighth nerve. Wave II comes from the proximal portion of the eighth nerve. Wave III comes from the cochlear nucleus. Wave IV comes the superior Olivatory complex then the wave V formation happens at the level of lateral lemniscus termination in the inferior colliculus. For wave VI and VII formation, sites are poorly understood but may come from the medial Geniculate body (MGB). The entire waveform should be completed within 5 to 7 milliseconds following the onset of the stimulus. Let's see how these waves are recorded. There are three surface electrodes used at a time. The first electrode is placed over the forehead, known as the ground electrode. The second electrode is placed over the vertex and the third electrode is placed behind the pinna or over the mastoid bone, the stimulus is presented to the patient through standard headphones and sometimes through the use of an insert earphone. The stimulus used is mostly click, which occurs at a rate of 11 to 25 clicks per second. Now we see the application of auditory brainstem responses in our clinical practice.
Establishing the hearing threshold by BERA test gives a piece of very important information which is a hearing threshold in a newborn baby, uncooperative children, difficult to test patients, or a malingering patient. ABR threshold assessment is generally done with either click or tone-burst stimuli. The stimulus is initially presented at a level of 75 decibels and Wave V is identified and its latency measured. if no waves are present at this level the intensity of stimuli is increased by 10 decibels until all reliable and repeatable waveforms are generated. the test then proceeds by reducing the intensity of stimuli by 10 decibels and again measuring and recording the latency of Wave V. As the intensity of stimuli is reduced, the latency of wave V will increase and the amplitude of the wave V will decrease. When wave V can no longer be seen, this intensity level may be taken as the threshold of hearing, which is usually within 10 decibels of actual hearing.
since the threshold search is commonly done using click stimuli, it may be noted that frequency-specific information is not accurate in this test because click stimuli normally stimulate the cochlea between 1500 and 4000 hertz. hence this test can underestimate or misidentify a patient as normal, who manifests a low-frequency hearing loss or even it may overestimate the hearing loss in a high-frequency hearing deficit patient. For frequency-specific information, middle latency responses (MLR) may be used with tone burst stimuli at 500, 1000, 2000, and 4000 Hz. So BERA test has to be interpreted carefully having scientific knowledge of click and tone burst stimuli contemplating the sites of waveform generation and in context with reports of other tests and clinical judgment of the clinician.
Apart from hearing threshold estimation in the above category patients, the other uses of ABR include neurodiagnostic especially in cases of asymmetrical hearing loss, tinnitus, and vertigo. ABR is also used in a special group of patients who have normal Otoacoustic emissions (OAEs) still is not able to hear the sound and there might be a problem in the auditory nerve pathways and this kind of hearing loss can be explained by Auditory neuropathy. Auditing neuropathy is a group of disorder where there is some lesion in the auditory nerve or auditing nerve pathways but the cochlea and the conductive Apparatus of hearing is normal and these patients, though, forms a very less number but sometimes it comes as a surprise when pure tone audiometry is normal yet the patient claims he has not heard. In such cases, diagnosis of Auditory neuropathy should be considered
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17 июл 2024
