What are the possible causes of variations in the caloric, rotational chair, and vHIT test results?

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It is likely that caloric, rotational chair, and vHIT (video head impulse test) test results may differ depending on the site. Patients with vestibular dysfunction symptoms often undergo a detailed diagnostic workup. Caloric testing can assess and quantify the functional status of the individual's vestibular systems. The test utilizes the mechanics of the vestibular-ocular reflex (VOR) to test for a unilateral peripheral deficit. These levels of stimulation are significantly lower than those experienced by the VOR system daily and may not identify dysfunction at higher frequencies. The rotational chair test commonly stimulates frequencies in the range of 0.01 to 1.28 Hz.

Head autorotation, an alternative method of testing VOR, stimulates frequencies of 1 to 6 Hz. The rotational chair test has primarily been used for analyzing horizontal canal VOR. Video Head Impulse Test (vHIT) is now widely used to test the function of each of the six semicircular canals individually by measuring the eye rotation response to an abrupt head rotation in the plane of the canal. The main measure of canal adequacy is the ratio of the eye movement response to the head movement stimulus, that is, the gain of the vestibular-ocular reflex (VOR). vHIT and caloric evaluate the vestibular system in different frequency ranges.

Dissociation in test findings may be related to changes in measurable vHIT results as compensation progresses, whereas the caloric asymmetry remains more stable. If, after the initial history and physical exam, acute vestibular neuritis is in the differential but is not certain, vHIT should be considered as part of the diagnostic workup. Further vestibular testing is unnecessary if that proves to be abnormal in the acute setting.

For chronic patients, vHIT is still an appropriate first test. However, if, after the acute phase, the vHIT results normalize, caloric testing should be performed to rule out ongoing peripheral disease. For fluctuating vestibulopathy, the literature suggests preferentially doing caloric testing. However, for pathologies such as BPPV, that adds minimal diagnostic value.

I hope this helps.