Abstract
Harmonic acceleration tests in the yaw plane with the head centered or in an eccentric position 90cm from the axis of rotation were performed in 41 patients with unilateral canal paresis due to vestibular neuronitis and sudden deafness, Meniere's disease and benign paroxysmal positional vertigo (BPPV). In the eccentric VOR at 0.32 and 0.6Hz, gain enhancement and phase lead were observed in the normal subjects. In the eccentric VOR, subjects were stimulated both by angular acceleration, as well as linear centrifugal and tangential acceleration, which act on the otolith organs. At 0.32 and 0.64Hz in this position, tangential acceleration showed a higher value than centrifugal acceleration. Therefore, we concluded that the gain enhancement and phase lead in the eccentric VOR were derived from tangential acceleration acting on the utriculus.
The patients with vestibular disorders other than BPPV showed normal gain enhancement and phase lead at 0.32 and 0.64Hz. However, patients with BPPV, showed no gain enhancement or phase lead in 53.3% and 73.3% of the patients, respectively.
It is suggested that BPPV results from incorrect response of the cupola in the posterior semicircular canal to gravitational changes due to otolithiasis. Therefore, the loss of gain enhancement and phase lead in the eccentric VOR in the patients with BPPV may be the result of utricular dysfunction.
