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