Semicircular canal plane head impulses detect absent function of individual semicircular canals

Abstract

We studied the human vestibulo-ocular reflex (VOR) in response to head 'impulses': brief, unpredictable, passive, high-acceleration (up to 4000 degrees/s2), low-amplitude (20-30 degrees) head rotations. We delivered the head impulses approximately in the plane of the semicircular canal (SCC) being tested. To test the anterior and posterior SCCs, the head impulses were delivered in a diagonal plane, midway between the frontal (roll) and sagittal (pitch) planes. We recorded head and eye position in three dimensions with scleral search coils in nine normal subjects, seven patients following unilateral surgical vestibular neurectomy and three patients following unilateral posterior SCC occlusion. In the post-surgical patients we demonstrated a severe, permanent VOR gain deficit (0.2-0.3) for head impulses directed toward any single non-functioning SCC. The sensitivity of the test depends on the physiological properties of primary vestibular afferents, and its specificity depends on the anatomical orientation of the SCCs. The diagonal head impulse is the first test of individual vertical SCC function in humans, and together with the horizontal head impulse, forms a comprehensive battery of SCC-plane tests. These canal-plane impulses could be useful in evaluating patients with vertigo or other vestibular disorders.

Dynamic Visual Acuity during Passive Head Thrusts in Canal Planes

“…We recommend using this cutoff as the criterion reference point for abnormal htDVA. The similarity in htDVA score across canals is in contrast to the difference between vertical and horizontal canal plane VOR gains during passive headthrust testing (Cremer et al 1998). One possible explanation for the difference is that the htDVA test allows subjects multiple opportunities to identify the optotype with multiple trials for each acuity level.…”

“…For example, when testing the LA and RP canal pair, the sensor was placed at 45-right (subject's perspective) off the midsagittal line bisecting the skull, after pitching the head to bring Reid's line õ20-nose down ( Fig. 1; Cremer et al 1998;Della Santina et al 2005). Horizontal head thrusts to assess horizontal canal function were performed first, followed by either RALP or LARP head thrusts.…”

Changes in the Three-Dimensional Angular Vestibulo-Ocular Reflex following Intratympanic Gentamicin for Ménière's Disease

“…The positive ends of these axes pointed out the nose, left ear, and top of the head, respectively. We then rotated the coordinate system + 45°around the z-axis so that the new coordinate axes roughly aligned with the axes of head rotation, axes that lay perpendicular to the canal planes (Cremer et al 1998). The 3D eye and head velocity vectors then had components corresponding to each of the three canal planes.…”

“…Subjects with SUVD indeed have markedly diminished gains for head thrusts that would excite the canals on the lesioned side (Aw et al 1996b). Head thrusts in the planes of the vertical semicircular canals likewise demonstrate hypofunction and can even isolate hypofunction affecting only one canal (Aw et al 1995a,b;Cremer et al 1998Cremer et al , 2000Minor et al 2001).…”

Video Head Impulse Test (vHIT): Main Concepts

“…The possibility of examining each of the six semicircular canals separately introduces a revolutionary change in clinical neurotology and may in time contribute to newer diagnostic possibilities, particularly when associated with the electrical responses of the saccule and utricle (cervical and ocular VEMP) [5][6][7][8]. But, is important to salient that, vHIT is a complementary test, which adds information for the vestibular evaluation.…”