Decreases in Cerebral Blood Flow When Upright Are Related to Vestibular Function Regardless of Age

Abstract

IntroductionDecreases in cerebral blood flow occur when moving from the supine to upright posture, yet the cause remains unclear. We hypothesized that impaired vestibular function would produce greater drops in cerebral blood flow in the upright posture.Methods155 subjects were screened for otolith function and based on ocular counter‐roll (OCR), 21 were classified as either young low (YL), young high (YH), old low (OL) or old high (OH). Mean OCR ‐ YL & OL ‐ 0.08±0.05; YH & OH 0.22±0.05. Age for young 33±12, old 69±6 years. Subjects underwent two 30‐min tilt tests on separate days. Cerebral flow velocity (CFV), by TCD, blood pressure (Finapres) and end‐tidal CO2 were measured continuously.ResultsReduced otolith function was associated with significantly greater drops in CFV at all ages (YL: ‐20±4%; OL: ‐22±3%) as compared to normal function (YH: ‐8±2%; OH: ‐13±2%), despite the fact that blood pressure changes were similar in all groups. The reduced OCR groups also demonstrated greater postural hypocapnia (YL: ‐3±1mmHg; OL: ‐4±1mmHg) vs (YH: ‐1±1mmHg; OH: ‐2±1mmHg), however this hypocapnia could only explain ~9‐12% of the 20‐22% decrease in CFV..DiscussionThese data demonstrate that otherwise healthy subjects of all ages with impaired vestibular function demonstrate greater decreases in cerebral blood flow when upright. Thus, vestibular function may play an important role in cerebral orthostatic response.