Theoretical models for the mechanisms of benign paroxysmal positional vertigo.

Benign paroxysmal positional vertigo (BPPV) is a common vestibular disorder resulting from a malfunction of the semicircular canal. Prior studies attempting to elucidate the mechanics of BPPV have focused on clinical and laboratory findings, and have discussed theoretical aspects only in qualitative terms. The goal of this study is to create a mathematical description of BPPV mechanics based on biophysical principles, in order to improve the physiopathological understanding of the most common varieties of the disorder, canalithiasis and cupulolithiasis. First, the abnormal stimulus being applied to the vestibular system during BPPV episodes is estimated by an analysis of the vestibulo-ocular reflex (VOR) response of clinical BPPV patients. The magnitude and time course of the head motion stimulus that would, in a normal test subject, produce a VOR response similar to that observed during BPPV nystagmus are inferred from eye motion data using an inverse transfer function approach. Next, physicomathematical models to describe the mechanics of the abnormal stimulations of the crista are created: the cupulolithiasis model is based on the principle that dense particulate matter becomes attached to the cupula of affected patients and effectively changes the specific gravity of the cupula; the canalithiasis model is based on the hydrodynamic effects from a cluster of particles falling within the canal endolymph. The stimuli predicted by these two models are compared to the stimuli estimated from physiological and clinical studies. The model predictions are found to be consistent with the empirical evidence for a reasonable set of model parameters. The cupulolithiasis model predicts a value of 0.69 micro g as the mass of particles contributing to the disorder. The canalithiasis model predicts a value of 0.087 micro g. These results support and expand our understanding of the mechanisms underlying the production of the cupulolithiasis and canalithiasis varieties of vertigo in humans. On the basis of these models, several predictions that can help the clinician improve the evaluation of BPPV patients are discussed.