2013 BC Balance and Dizziness Disorders Society Awards
A total of $10,000 in grants for research into improving treatment of balance and dizziness disorders was awarded in the second year of our awards program. To a research group at the University of British Columbia (UBC) went $5000; an equal amount was awarded to a group at St. Paul’s Hospital in Vancouver.
Read about the 2013 projects:
Led by Dr. Mark Carpenter, Canada Research Chair Physical Activity and Health, School of Kinesiology, UBC. Other researchers: Dr. Jane Lea and Dr. Brian Westerberg, St. Paul’s Hospital, Vancouver; Dr. John Allum, University of Basel, Switzerland; Dr. Tim Inglis and graduate students Taylor Cleworth and Eduardo Naranjo, School of Kinesiology, UBC.
Summary of project: Growing evidence suggests that the vestibular system can be influenced by fear and anxiety. Studies have shown that a fear of falling is frequently reported with vestibular disorders. Research also suggests that there are significant relationships between anxiety and common vestibular symptoms – increases in both balance instability and vertigo are reported in those that have high fear of falling.
The mechanisms for such an anxiety and fear interaction are currently unknown. Some evidence from studies in animals suggests a direct connection from the areas in the brain that process fear, anxiety and arousal to the vestibular nuclei. There is, therefore, the potential that as humans become more fearful, there may be an influence on the vestibular reflexes. These include the:
- vestibulo-ocular reflex (VOR) – reflex pathway that goes to the muscles of the eyes and allows you to maintain your gaze on a fixed target as you move your head; and
- vestibulo-spinal reflex (VSR) – the reflex pathway that goes via the spinal cord to the muscular system below the neck.
The functioning of these reflex pathways can be measured by the vestibular-evoked myogenic potential (VEMP) test. During the VEMP test, headphones are worn and small electrodes are attached to the skin over the:
- cervical (neck) muscles – cVEMP test;
- ocular (eye) muscles – oVEMP test; or
- leg muscles – leg VEMP test (not commonly used as a clinical test).
A series of high-intensity clicks or tones is transmitted through the headphones in a number of presentations. Each individual sound will activate the vestibular organ as projected along the vestibular nerves, resulting in a tiny twitch of the muscles over which the electrode is placed.
Dr. Carpenter's research group used VEMP tests to ask their first question: Can fear influence the gain or size of the response going through the vestibular reflex pathways? To determine an answer, they compared the VEMP responses in the eye, neck and leg muscles under fearful and non-fearful conditions to see if they change. Twenty-five young healthy adults, known to have normally functioning vestibular systems, were asked to stand on a hydraulic lift that could be raised to initiate a fear of falling. VEMP tests were done when the subjects were not fearful – standing near ground height and away from the edge of the lift platform. The same tests were repeated when the subjects became fearful – standing at the edge of the platform at a height of 3.2 metres.
The body undergoes physiological changes when standing at high heights – fear, anxiety and physiological arousal all increase. At the same time, confidence and perceived stability decrease. These changes are measurable by electrodes placed on the skin, similar to a lie-detector test: by measuring them as the VEMP tests were performed, the researchers were able to verify that the subjects were fearful, anxious and aroused when the lift was at height. It is very difficult to suppress our natural fear of falling a distance: even though the subjects wore a safety harness and knew they could not fall, they still had a strong fear response.
The results of the experiment showed a significant increase in the amplitude of the vestibular-evoked response when the subjects were fearful. And those that were more highly aroused had a higher vestibular response to the same stimulus.
The second question asked: Can fear influence the gain of the vestibular reflex pathways? To find an answer, the vestibulo-ocular reflex (VOR) was measured using the video head impulse test (vHIT). The VOR stabilizes the gaze on a target as the head is moved. During the vHIT test, special goggles are worn that measure both head velocity and eye velocity. The clinician provides a quick rotation of the head and looks for the opposite movement of the eyes. In a normal functioning vestibular system, the ratio between these movements should be close to one.
The vHIT test was done in a similar manner to the VEMP test, with the subjects standing at a low height, then raised to 3.2 metres. The head was rotated both horizontally (back-and-forth) and vertically (up-and-down). In both cases, there was a significant gain in the vestibulo-ocular reflex when the subjects were fearful. Again, those with a larger arousal response had a larger vHIT.
The third question asked: Does Fear Influence Eye Movements Independently? To find an answer, three different types of eye movements were tested to compare changes under non-fearful and fearful conditions:
- eye saccades – rapid eye movements that allow the eye to “jump” from one fixed target to another;
- smooth pursuit – smooth movements that allow the eye to track a moving target; and
- optokinetic reflex – a combination of eye saccade and smooth pursuit movements that enables following a moving object with the eyes and, when it moves out of the field of vision, automatically moves the eye back to the position it was in when the object was first seen.
Eye saccades and smooth pursuit movements do not involve the vestibular system; they just involve the use of brainstem nuclei that control eye muscles. The optokinetic reflex, however, relies on the vestibular system.
The subjects were tested wearing electrodes around the eye to measure accurately these three types of eye movements under non-fearful conditions (standing close to ground level) and fearful conditions (standing on a raised platform).
The outcome of the tests changed when people were fearful:
- the velocity and accuracy of eye movement increased during the eye saccade task;
- eye movement was faster during the smooth pursuit task; and
- a higher gain of the movement of the eye to the target during the optokinetic test.
The results of the project indicate that both of the reflex pathways involved in vestibular function are influenced by fear. In addition, fear seems to influence the reflexive eye movements that rely on vestibular function as well as those that do not.
The tests done on healthy young subjects for this project are the same as those commonly used in diagnostic clinics to sort out if someone with a balance problem has an issue involving vestibular function or some other central deficit. It is useful for clinicians to know that the emotional state of the individual being tested may influence the clinical vestibular assessment outcome.
The results of this project will help guide the development of new treatment
St. Paul’s Group
Led by Dr. Jane Lea, otologist/neurotologist and pediatric otolaryngologist. Other researchers: Dr. Maggie Aaron and Dr. Brian Westerberg of St. Paul's, and Dr. Mark Carpenter of UBC.
Summary of project: There are two main vestibular components in the inner ear: the semicircular canals and the otolithic organs (utricle and saccule). The otolithic organs tell us whether we are accelerating or decelerating (speeding up or slowing down), whereas the semi-circular canals tell us whether we are turning. Unlike the semicircular canals, the function of the utricle and saccule is less understood, and diagnostic tests for disorders involving these organs are not well established.
Current methods for otolithic testing involve a number of limitations that may be improved upon by using a technique called translational vestibulo-ocular reflex (tVOR) testing. This involves using a motorized sled to rapidly shift the whole body of the patient in different directions while examining the resulting reflexive movements of the eyes. This study was designed to examine the effectiveness of tVOR tests to detect different types of otolith dysfunction, compared with other more common clinical tests of otolith function, including subjective visual vertical and vestibular-evoked myogenic potential tests.
Significance of research: Our current understanding of certain inner ear disorders is lacking, especially when it comes to the otolithic organs. Although we currently have several tests of these important end organs, the diagnostic utility of these tests is subject to great controversy. There is uncertainty about what the tests actually mean, and this subsequently affects our ability to properly diagnose, counsel and treat patients.
This study of tVOR will enhance our ability to properly diagnose and treat this largely misunderstood cause of balance disorders. Given that tVOR more closely mimics how we actually use our otolithic organs on a day-to-day basis, we hypothesize that this test will provide a better assessment. In addition, tVOR may shed light on the currently used otolithic tests (SVV and VEMPs) in terms of deciphering the site of lesion and improving diagnostic utility. Improved diagnostic utility will ultimately enhance patient care with more accurate diagnosis, counselling and treatment.