Impaired Vestibular Function affects Orthostatic Cerebral Blood Flow Response

Abstract

Introduction: Falls in the elderly remain an important and poorly understood problem. Vestibular function that can directly affect autonomic and blood pressure regulation is lost with aging. Thus we hypothesized that impaired vestibular function produces greater cerebral hypoperfusion in the upright posture. Methods: Based on ocular torsion, subjects were classified as having normal (C) or impaired (I) vestibular function (I: 74 + 2; C: 73 + 1 years old). Subjects underwent a 30-min tilt test while blindfolded. Cerebral flow velocity (CFV), by TCD, blood pressure (Finapres) and end-tidal CO2 were measured continuously. Results: The impaired subjects had a greater decrease in CFV during the first min of tilt (I: −26 ± 5; C: −4 ± 2 %, P<0.05) compared to the controls, with no significant changes in blood pressure. This was associated with a significantly greater hypocapnia in the impaired group (I, −5.2 ± 0.8; C, −3.0 ± 0.5%), however using individual cerebrovascular reactivity, only 9 of the 26% decrease in CFV in the impaired group could be explained by hypocapnia while all of the cerebral hypoperfusion could be explained in the normal group. Thus the vestibularly impaired group demonstrated a ~17% decrease in CFV unrelated to hypocapnia or blood pressure. Consistent with a role for vestibular inputs, CFV changes were strongly correlated to ocular torsion (R2=0.94). Discussion: These data demonstrate that otherwise healthy elderly subjects with impaired vestibular function demonstrate an impaired cerebral blood flow response to the upright posture, suggesting an important role for vestibular function in cerebral orthostatic response. Supported by NASA.