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The impact of shear rate and prolonged sitting on endothelial function in children Armstrong, Victoria

Abstract

Prolonged sitting has been shown to impair endothelial function in children, yet the mechanisms underlying this remain unclear. In adults, there is a decline in endothelial function, indexed using flow-mediated dilation (FMD), after 1 hour of sitting. When localized heating was used to increase shear stress, the sitting-induced reduction in FMD can be prevented, confirming this decline was shear-stress mediated. The relationship between FMD and shear stress is weaker in children and whether limb heating increases shear stress and FMD in children is unknown. We therefore examined the time-course of changes in FMD with sitting and whether increasing shear stress during sitting would prevent reductions in FMD. Sixteen children completed measurements of superficial femoral artery (SFA) FMD in both legs before and after a 3-hour sitting period, with a subgroup of 7 children completing additional measures after 1 and 2 hours of sitting. In one leg, the calf was heated with an electronic heat pad at 42°C (i.e. heated condition), while the contralateral leg served as an internal control (i.e., non-heated condition). Heart rate and blood pressure were unchanged throughout the 3 hours confirming the heating was localized. Following 3 hours of sitting, antegrade shear rate was unchanged in the non-heated leg (pre-sit: 102.0 ±43.7 s-¹, 3 hr sit: 126 ±40.1 s-¹; P>0.05), but increased significantly in the heated leg (pre-sit:102.2 ±33.6 s-¹, 3 hr sit: 216.2 ±47.3 s-¹; P

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