Abstract

The semicircular canals sense angular acceleration and are arranged in roughly parallel pairs. The vestibuloocular reflex (VOR) is responsible for maintaining binocular fixation and stabilizing binocular foveal images during head movements. The VORs are divided into two types: angular and linear. Angular reflexes are initiated by activation of the semicircular canals. There are several kinds of test for semicircular canal function such as caloric test, rotation test, and pulse step sine test. Caloric testing remains the most useful laboratory test in determining the responsiveness of a labyrinth. It is one of the few tests that allow one labyrinth to be studied independently of the other. The stimulus can be applied relatively easily with techniques that are commonly available. Caloric testing relies on stimulating or cooling the vestibular system by alternately heating and cooling the external auditory canal with water or air. Rotational tests analyze the responses of both labyrinths together. They require a high-torque motor-driven chair and relatively advanced software to analyze the results. Rotatory chair testing is useful in assessing vestibular function in patients with suspected bilateral vestibular hypofunction and children. Step changes in head velocity can be used instead of sinusoidal rotations to identify vestibular hypofunction. Time constant are determined by the time after onset of the stimulus at which slow phase eye velocity has decreased by 67% of its initial value. The use of a novel “pulse-step-sine” (PSS) rotational stimulus can identify abnormal function of the horizontal semicircular canals in human subjects with unilateral and bilateral vestibular deficits. Research in Vestibular Science 2009;8(2 suppl 1):S22-S30