Alex N. Pomeroy, Katie Stanford, Lee Stoner, FACSM. University of North Carolina at Chapel Hill, Chapel Hill, NC.

PURPOSE: A primary risk factor for dementias is atherosclerosis of the cerebral arteries. Prolonged sitting has been associated with precursors to 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 is a plausible pathway. The purpose of this study was to investigate the relationship between VBP and changes in CBF. METHODS: Five participants (n = 5, 23.6 [5.3] y, 40% F, 23.1 [3.2] kg/m2) underwent two conditions in a randomized cross-over trial, both with a two-hour sitting bout: CUFF, where bilateral occlusive cuffs were applied to the legs to induce venous pooling and NON-CUFF, where occlusive cuffs were applied, but not inflated as a control condition. CBF was measured with mean volumetric blood flow through the common carotid artery using duplex Doppler ultrasound. Shear rate was calculated to determine changes in forces on the cerebral arteries. Results were analyzed using a random-effects mixed model, and effect sizes were reported using Cohen’s d. RESULTS: The interaction effect between time and condition was significant (ß = 35.91 ml/min, ES = 1.00) for CBF. CBF decreased 3.7% for CUFF and increased 19.5% in the NON-CUFF condition. Similarly, there was a significant interaction effect between time and condition for shear rate (ß = 62.9 s-1, ES = 0.72). Shear rate increased 1.9% in the CUFF condition and increased 25.8% in the NON-CUFF condition. CONCLUSIONS: CBF decreased in the CUFF condition, while increasing in the NON-CUFF condition over time. Positive shear rate increased slightly in the CUFF condition, but increased greatly in the NON-CUFF condition. These effects indicate VBP may be a driver of CBF and shear stress changes in the cerebral vasculature.

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