THE ROLE OF VENOUS BLOOD POOLING DURING PROLONGED SITTING ON CEREBRAL BLOOD FLOW

Abstract

PURPOSE: A primary risk factor for dementias is atherosclerosis of the cerebral arteries. Prolonged sitting has been associated with precursors of atherosclerosis, including acute reductions in cerebral blood flow (CBF) and concomitant reductions in shear stress, but the mechanism for cerebral hemodynamic changes is unclear. Venous blood pooling (VBP) in the calves due to gravity has been suggested as a potential cause for acute hemodynamic changes in the central vasculature, but the claim hasn’t been evaluated in the cerebral vasculature. METHODS: 5 participants (n = 5, 23.6 [5.3] y, 55% F, 23.1 [3.2] kg/m2) underwent two conditions, both with a two-hour sitting bout: CUFF, where bilateral occlusive cuffs were applied to the legs to induce venous pooling and NON-CUFF, which was a control condition. CBF was measured with mean volumetric blood flow through the common carotid artery measured with doppler ultrasound. Shear rate was measured to determine changes in shear stress. Results were analyzed using a random-effects mixed model and Cohen’s d for effect size. RESULTS: The interaction effect between time and condition was significant (ß = 35.91, ES = 1.00) for CBF. CBF decreased 3.71% in the CUFF condition on average, whereas it increased 19.50% on average in the NON-CUFF condition. There was a significant main effect for time for positive shear rate (ß = 36.5, ES = 0.72), but the main effect for condition was not statistically significant (p = 0.396). CONCLUSIONS: CBF decreased in the CUFF condition more than in the NON-CUFF condition over time, so VBP may be a driver of hemodynamic changes in the cerebral vasculature. These changes occurred in the presence of decreased positive shear rate over time in both conditions, indicating the effect may be independent of shear stress-mediated hemodynamic changes.