Tracking the progress of peripheral Vestibular disease with the video Head Impulse Test

While the introduction of the video Head Impulse Test (vHIT) in 2009 revolutionized the diagnosis of vestibular disease, providing a measurement of the function of all six semicircular canals, this thesis aimed to determine the utility of tracking peripheral vestibular disease over time. Initial requirements were to analyze the factors affecting the quantitative output of the vHIT test and to develop practical techniques to ensure the output reflects the function of the tested canal. This included recognizing and avoiding artefacts, and an analysis of the interacting 3-D factors contributing to the 1-D output. Then, testing a cohort of normal subjects produced the age-matched range of normal vestibular ocular reflex (VOR) gain values for comparison against patient results. Subsequently, the vHIT and caloric responses of patients with Ménière's disease were examined, showing a dissociation between the tests. A thermo-fluid model was developed to explain this dissociation. Long-term vHIT tracking of a patient following sequential neuritis showed his peripheral function recovery took longer than expected, with a time constant of 150 days for the recovery of high-head-velocity horizontal responses. These results also suggested a way to tease out the relative contributions of peripheral gain change and central compensation to the patient’s overall functional VOR recovery. Finally, for patients requiring systemic gentamicin, the vHIT tracking data showed that early, often-repeated testing is necessary to detect the onset of vestibulo-toxic damage. If damage does occur, it is then necessary to continue vHIT tracking after the dosage regime has stopped, as function may continue to deteriorate. Thus, this thesis concluded unequivocally that tracking the progress of peripheral vestibular disease with correctly performed video Head Impulse Tests is both practical and extremely useful

Reduction of ocular counter-rolling by adaptation to space

We studied the three-dimensional vestibulo-ocular reflex (VOR) of rhesus monkeys before and after the COSMOS Biosatellite 2229 Mission of 1992-1993. This included tests of ocular counter-rolling (OCR), the gain of the vestibulo-ocular reflex (VOR), and spatial orientation of velocity storage. A four-axis vestibular and oculomotor stimulator was transported to the Institute of Biomedical Problems in Moscow for the pre- and postflight ground-based testing. Twelve normal juvenile male rhesus monkey were implanted surgically with eye coils and tested 60-90 days before spaceflight. Two monkey (7906 and 6151), selected from the twelve as flight animals, flew from 12/29/92 to 1/10/93. Upon recovery, they were tested for 11 days postflight along with three control animals. Compensatory ocular torsion was produced in two ways: (1) Lateral head tilts evoked OCR through otolith-ocular reflexes. OCR was also measured dynamically during off-vertical axis rotation (OVAR). (2) Rotation about a naso-occipital axis that was either vertical of horizontal elicited torsional nystagmus through semicircular canal-ocular reflexes (roll VOR). OCR from the otoliths was substantially reduced (70 percent) for 11 days after reentry on both modes of testing. The gain of the roll VOR was also decreased, but less than OCR. These data demonstrate that there was a long-lasting depression of torsional or roll eye movements after adaptation to microgravity in these monkeys, especially those movements produced by the otolith organs

The Video Head Impulse Test

In 1988, we introduced impulsive testing of semicircular canal (SCC) function measured with scleral search coils and showed that it could accurately and reliably detect impaired function even of a single lateral canal. Later we showed that it was also possible to test individual vertical canal function in peripheral and also in central vestibular disorders and proposed a physiological mechanism for why this might be so. For the next 20 years, between 1988 and 2008, impulsive testing of individual SCC function could only be accurately done by a few aficionados with the time and money to support scleral search-coil systems-an expensive, complicated and cumbersome, semi-invasive technique that never made the transition from the research lab to the dizzy clinic. Then, in 2009 and 2013, we introduced a video method of testing function of each of the six canals individually. Since 2009, the method has been taken up by most dizzy clinics around the world, with now close to 100 refereed articles in PubMed. In many dizzy clinics around the world, video Head Impulse Testing has supplanted caloric testing as the initial and in some cases the final test of choice in patients with suspected vestibular disorders. Here, we consider seven current, interesting, and controversial aspects of video Head Impulse Testing: (1) introduction to the test; (2) the progress from the head impulse protocol (HIMPs) to the new variant-suppression head impulse protocol (SHIMPs); (3) the physiological basis for head impulse testing; (4) practical aspects and potential pitfalls of video head impulse testing; (5) problems of vestibulo-ocular reflex gain calculations; (6) head impulse testing in central vestibular disorders; and (7) to stay right up-to-date-new clinical disease patterns emerging from video head impulse testing. With thanks and appreciation we dedicate this article to our friend, colleague, and mentor, Dr Bernard Cohen of Mount Sinai Medical School, New York, who since his first article 55 years ago on compensatory eye movements induced by vertical SCC stimulation has become one of the giants of the vestibular world

A review of the geometrical basis and the principles underlying the use and interpretation of the video head impulse test (vHIT) in clinical vestibular testing

This paper is concerned mainly with the assumptions underpinning the actual testing procedure, measurement, and interpretation of the video head impulse test—vHIT. Other papers have reported in detail the artifacts which can interfere with obtaining accurate eye movement results, but here we focus not on artifacts, but on the basic questions about the assumptions and geometrical considerations by which vHIT works. These matters are crucial in understanding and appropriately interpreting the results obtained, especially as vHIT is now being applied to central disorders. The interpretation of the eye velocity responses relies on thorough knowledge of the factors which can affect the response—for example the orientation of the goggles on the head, the head pitch, and the contribution of vertical canals to the horizontal canal response. We highlight some of these issues and point to future developments and improvements. The paper assumes knowledge of how vHIT testing is conducted

The Video Head Impulse Test

In 1988, we introduced impulsive testing of semicircular canal (SCC) function measured with scleral search coils and showed that it could accurately and reliably detect impaired function even of a single lateral canal. Later we showed that it was also possible to test individual vertical canal function in peripheral and also in central vestibular disorders and proposed a physiological mechanism for why this might be so. For the next 20 years, between 1988 and 2008, impulsive testing of individual SCC function could only be accurately done by a few aficionados with the time and money to support scleral search-coil systems—an expensive, complicated and cumbersome, semi-invasive technique that never made the transition from the research lab to the dizzy clinic. Then, in 2009 and 2013, we introduced a video method of testing function of each of the six canals individually. Since 2009, the method has been taken up by most dizzy clinics around the world, with now close to 100 refereed articles in PubMed. In many dizzy clinics around the world, video Head Impulse Testing has supplanted caloric testing as the initial and in some cases the final test of choice in patients with suspected vestibular disorders. Here, we consider seven current, interesting, and controversial aspects of video Head Impulse Testing: (1) introduction to the test; (2) the progress from the head impulse protocol (HIMPs) to the new variant—suppression head impulse protocol (SHIMPs); (3) the physiological basis for head impulse testing; (4) practical aspects and potential pitfalls of video head impulse testing; (5) problems of vestibulo-ocular reflex gain calculations; (6) head impulse testing in central vestibular disorders; and (7) to stay right up-to-date—new clinical disease patterns emerging from video head impulse testing. With thanks and appreciation we dedicate this article to our friend, colleague, and mentor, Dr Bernard Cohen of Mount Sinai Medical School, New York, who since his first article 55 years ago on compensatory eye movements induced by vertical SCC stimulation has become one of the giants of the vestibular world

Modified head impulse procedure for vertical semicircular canals.

<p>Head impulses for RALP (right anterior – left posterior), LARP (left anterior – right posterior) and lateral canal stimulation (arrows), as viewed from the fixation point. For testing the vertical canals, a modified procedure has been used, which elicits mainly vertical eye movements to dispense with complex video processing of torsional eye movements <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0061488#pone.0061488-Migliaccio1" target="_blank">[7]</a>: The person's head is positioned turned with respect to the body, so that gaze is directed along the plane of head rotation in the direction of the named canals as represented by the vertical arrows. For testing horizontal canals the movement is in the plane of the horizontal canals as shown. These images are modified from the free iPhone or iPad app ‘aVOR’ developed by the first author <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0061488#pone.0061488-MacDougall3" target="_blank">[19]</a>. For the examination procedure, see also accompanying <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0061488#pone.0061488.s004" target="_blank">Video S1</a>.</p

VOR regression plots from coils vs. video for lateral, anterior and posterior canals.

<p>The coefficients of determination (R²) for each regression are listed. In each case the correspondence is extremely strong as shown by both graphical data and statistical analysis.</p