Clinical application of the head impulse test of semicircular canal function

Abstract

Objective: To review the theory, the validity and the clinical application and the new developments of the video head impulse test (vHIT) of semicircular canal function. vHIT has now superseded the caloric test as the first-line clinical test for vestibular patients. Outcomes: This review examines the origin and rationale for vHIT: how it is carried out; pitfalls in testing; the validation of the test; the interpretation of overt and covert compensatory saccades in patients with vestibular loss; how the area VOR gain is calculated. Results: The advantages of the test are considered: it is so innocuous that it can be given to patients even during acute vertigo attacks, and given repeatedly at short intervals; it is very successful for testing young children; it tests all six semicircular canals, and, unlike the caloric test, provides measures of the absolute level of canal function and so is valuable for monitoring the effect of ototoxic antibiotics as well as identifying bilateral vestibular loss. Patients with Meni ere's disease have normal canal function, although their caloric results generally indicate otherwise, with hydrops being the possible cause for that divergence. vHIT has shown the new vestibular syndrome of bilateral loss of vertical canal function and it is now being used for identifying the likely cause of vertigo of patients arriving at a hospital Emergency Roomnormal semicircular canal function in such patients indicating increased probability of a stroke. The theory and application of the new, but already widely used, variant called the suppression head impulse test (SHIMPs) is explained. SHIMPs is even simpler and more intuitive than the standard vHIT test and probably even better for testing children. Conclusion: This review provides the theoretical foundations for the practical application of the clinical vHIT test which has revolutionized the clinical testing of semicircular canal function. Abbreviations: VOR: vestibulo-ocular reflex; HIT: head impulse test; vHIT: video head impulse testthe technology; HIMP: the head impulse testthe procedure; SHIMP: the suppression head impulse testthe procedure;

Functional Head Impulse Test in Professional Athletes: Sport-Specific Normative Values and Implication for Sport-Related Concussion

“…Accordingly, an optimal testing strategy would be to start testing the highest acceleration bin and, only if a deficit is present, progressively decrease the acceleration to identify where the pathological behavior stops. With such strategy, a handball player would require a minimum of 17 head impulses at 7,000 deg/s 2 (the maximum acceleration currently displayed on the fHIT interface) per semicircular canal to be identified as healthy, i.e., comparable to the number of impulses used in a valid head impulse test (51, 54, 55).…”

What Bárány’s Caloric Test Might Have Overlooked: The Primary Factor May Be the Middle Ear Muscles

“…Another drawback of the Bárány model is inconsistency with the other standard vestibular test, the video head impulse test (vHIT). The test was devised a decade or more ago and involves monitoring a subject's eye movements with a camera located inside a set of goggles while the head is given a sudden jerk in the plane of the horizontal canal [11]. The speed of the eyes' response, mediated by the vestibulo-ocular reflex (the eye muscles are aligned in the same plane as the semicircular canals), gives a measure of how well the horizontal canals are functioning.…”

“…The interesting point, however, is that the results of the caloric and vHIT tests often disagree, even though they are both supposed to be testing the integrity of the semicircular canals [11]. There are various degrees of dissociation.…”

“…Such nystagmus is called "paradoxical" because nystagmus is still elicited by warm and cold water. However, the most clear-cut separation between the two tests is seen in Meniere's patients, who may have greatly reduced or absent semicircular canal function as indicated by the caloric test, but have normal canals as shown by the vHIT test [11,[29][30].…”

“…Although in modern times the caloric test has become less common -it is unpleasant and takes much clinical time -it is still the gold standard for assessing balance problems [10]. Nowadays the vHIT test (the video Head Impulse Test) is more often employed because it is quicker, easier, and better tolerated, even though it cannot determine the side of weakness [11,12]. Bárány explained his findings in terms of circulation cells set up by a thermal gradient in the horizontal canal (the semicircular canal closest to the outer ear), likening endolymph in the canal to water heated by a hot stove [1,3,7].…”