Impact of prolonged sitting on lower and upper limb micro- and macrovascular dilator function

Abstract

What is the central question of this study? The prevalence of sedentary behaviour in the workplace and increased daily sitting time have been associated with the development of cardiovascular disease; however, studies investigating the impact of sitting on vascular function remain limited. What is the main finding and its importance? We demonstrate that there is a marked vulnerability of the vasculature in the lower and upper limbs to prolonged sitting and highlight the importance of physical activity in restoring vascular function in a limb-specific manner. Sedentary behaviour in the workplace and increased daily sitting time are on the rise; however, studies investigating the impact of sitting on vascular function remain limited. Herein, we hypothesized that 6 h of uninterrupted sitting would impair limb micro- and macrovascular dilator function and that this impairment could be improved with a bout of walking. Resting blood flow, reactive hyperaemia to 5 min cuff occlusion (microvascular reactivity) and associated flow-mediated dilatation (FMD; macrovascular reactivity) were assessed in popliteal and brachial arteries of young men at baseline (Pre Sit) and after 6 h of uninterrupted sitting (Post Sit). Measures were then repeated after a 10 min walk (~1000 steps). Sitting resulted in a marked reduction of resting popliteal artery mean blood flow and mean shear rate (6 h mean shear rate, -52 ± 8 s(-1) versus Pre Sit, P < 0.05). Interestingly, reductions were also found in the brachial artery (6 h mean shear rate, -169 ± 41 s(-1) versus Pre Sit, P < 0.05). Likewise, after 6 h of sitting, cuff-induced reactive hyperaemia was reduced in both the lower leg (-43 ± 7% versus Pre Sit, P < 0.05) and forearm (-31 ± 11% versus Pre Sit, P < 0.05). In contrast, popliteal but not brachial artery FMD was blunted with sitting. Notably, lower leg reactive hyperaemia and FMD were restored after walking. Collectively, these data suggest that prolonged sitting markedly reduces lower leg micro- and macrovascular dilator function, but these impairments can be fully normalized with a short bout of walking. In contrast, upper arm microvascular reactivity is selectively impaired with prolonged sitting, and walking does not influence this effect.

Figure 1

Schematic illustrating overall design of experimental protocol. Measurements taken at the time points of 2, 4, and 6 hours were made while the subject was in the seated position whereas the Pre Sit, Post Sit, and Post Walk measurements were taken while the subject was in a semi-recumbent position.

Figure 2

Mean resting blood flow of the popliteal (A) and brachial (B) arteries at experimental time points. Popliteal and brachial artery blood flow was reduced by sitting. However, popliteal, but not brachial, artery blood flow was restored after 10min of walking. Values are means ± SEM. *p<0.05 vs. Pre Sit; †p<0.05 vs. Post Walk.

Figure 3

Time course and area under the curve of hyperemic blood flow responses in the popliteal (A) and brachial (B) arteries at baseline (Pre Sit), after sitting (Post Sit) and after walking (Post Walk). Hyperemic blood flow responses to cuff occlusion, indicative of microvascular reactivity, were blunted by sitting. However, popliteal, but not brachial, artery hyperemic blood flow was restored after 10min of walking. Values are means ± SEM. *p<0.05 vs. Pre Sit; †p<0.05 vs. Post Walk.

Figure 4

Popliteal (A) and brachial (B) artery %FMD and FMD corrected for shear rate AUC at time points Pre Sit, Post Sit, and Post Walk. Popliteal, but not brachial, artery %FMD, indicative of macrovascular dilator function, was reduced with sitting and restored after a 10min walk. The effect of sitting on popliteal artery FMD remained after correcting for shear rate with ANCOVA analysis. Values are means ± SEM. *p<0.05 vs. Pre Sit; †p<0.05 vs. Post Walk.