Vertigo? Look between your ears Dr. David, M.D. and Dr. Shahnaz, PhD, Associate Professor of Audiology, gathering data in the auditory vestibular lab. Eytan A. David, M.D., F.R.C.S.C. Dr.EytanDavidisasubspecialistearsurgeonandOtolaryngologyconsultant at Lions Gate Hospital, British Columbia. He completed Neurotology- Skull Base Surgery Fellowship training at the University of Toronto. His practice is restricted to hearing and balance related disorders. He has been published in international peer-reviewed journals and is a consultant to the Worker’s Compensation Board Appeal Tribunal. He is a past president of the British Columbia Otolaryngology Society and a Clinical Instructor in the Department of Surgery at the University of British Columbia. The Vancouver Auditory Vestibular Clinic The inner ear is the chief organ of the human balance system. Each inner ear is comprised of three semicircular canals defined by their orientation in space as angle accelerometers, and two further receptors contained in the otolith; the utricle and saccule. The utricle and saccule convey horizontal acceleration and downward pull of gravity information. These balance portions of the inner ear are dynamic, in that they respond to linear and angular accelerations in real time. The change over time of their activity is the chief determinant of move- ment perception. There is a dynamic equilibrium that exists between the inner ears in which a constant resting pattern of signals from each side reaches the brain and is usually equal and opposite in nature, effectively ren- dering a stable “no significant difference” pattern deep in the brain, in an area called the pre pontine reticular formation. Motion produces a change in this dynamic equilibrium, with the pattern of discharge that is dis- tributed to the brain travelling via direct “hardwired” connections to the muscles governing eye position change. The brain interprets the unequal input as a con- dition of motion, which fits our definition of“vertigo”. When there is a change in the function of one of the organs of the vestibular system, the unequal intensity of discharges from the inner ear is detected by the brain as an imbalance, and the manifestation of this is typi- cally a sensation of rotary hallucination because the eye muscles are reflexively directed to deviate in a certain direction. The result of this eye position change is called nystagmus.Objectivebalancetestingholdsauniqueplace in the diagnosis and treatment of patients with dizziness because nystagmus can be recorded and measured. In our vestibular lab, we are able to test patients with the use of state-of-the-art four-channel video nystag- mography in order to record the function of the lateral semicircular canal in its slow wave velocity function and the subserving superior vestibular nerve. The two-camera system allows us to control for unrelated eye muscle abnormalities such as strabismus or convergence insufficiency. This represents the gold standard of objec- tive vestibular testing with a long established track record. More recent technology is used in our lab to help to determine dysfunction in all three semicircular canals in the fast wave component of their action, which may be more physiologically pertinent in dizzy patients. This testing is done via video head impulse testing (vHIT), which can measure visual gain in the presence of covert, or hidden, eye position changes (saccades). Our lab is at the forefront in the use of vestibular evoked myogenic potential testing (VEMPs). We will be publishing one of the largest series of normative data in both cervical and ocular VEMP tracings that can delineate abnormalities in inner ear gravity sensor (otolith) function. Our lab is also investigating the reemergence of electrocochleography (ECOG) in assessing patients with seemingly normal hearing who are unable to hear or understand speech in certain circumstances, known as“hidden hearing loss”. Finally, our auditory vestibular lab offers state-of-the-art hearing assessments for the delineation of central auditory processing disorders (CAPD) using behavioral audiomet- ric and objective electrophysiologic testing. Taken together, with a detailed history and directed neuro-otologic clinical examination, an experienced neuro-otologist and auditory vestibular team can reasonably be expected to evaluate the integrity of the inner ear hearing and balance system with an unprec- edented level of medical evidence. This is especially important because we know that the self report of imbalance symptoms is imprecise. For example, in a multicenter review of over 9000 patients presenting with symptoms of imbalance, less than one third of these patients were found to have an inner ear disorder. The term“vertigo”has also been shown to have diverse meaning for patients, general physicians and otolaryngologists. Identifying and diagnosing auditory vestib- ular disorders can now be reliably attained to the highest standards of evidence based medicine using the expertise and technolo- gy at theVancouver AuditoryVestibular Clinic. 27 | HEARING TODAY