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

Abstract

Sedentary behavior 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 hours of uninterrupted sitting would impair limb micro- and macrovascular dilator function and this impairment could be improved with a bout of walking. Resting blood flow, reactive hyperemia to 5 min cuff occlusion (microvascular reactivity) and associated FMD (macrovascular reactivity) were assessed in popliteal and brachial arteries of young men at baseline (Pre Sit) and after 6 hours 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-hr mean shear rate, −52±8 s−1 vs. Pre Sit, p<0.05). Interestingly, reductions were also found in the brachial artery (6-hr mean shear rate, −169±41 s−1 vs. Pre Sit, p<0.05). Likewise, following 6 hours of sitting, cuff-induced reactive hyperemia was reduced in both the lower leg (−43±7% vs. Pre Sit, p<0.05) and forearm (−31±11% vs. Pre Sit, p<0.05). In contrast, popliteal, but not brachial, artery FMD was blunted with sitting. Notably, lower leg reactive hyperemia 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.

Prolonged sitting-induced leg endothelial dysfunction is prevented by fidgeting

“…Our previous findings (19,20) and findings from others (15,26) that sitting causes endothelial dysfunction in the leg, but not the arm, fuel the idea that increased susceptibility of the leg vasculature to atherosclerosis may be, in part, attributable to the direct detrimental effects of prolonged sitting on that vasculature. Strategies such as fidgeting can offset the decay in leg blood flow and shear stress during sitting, thus preventing the consequent impairment of endothelial function and potentially providing important vascular benefits in the long term.…”

“…Along these lines, we (19,20) and others (15,25) have observed that during prolonged sitting, there is a marked reduction in blood flow and shear stress in the lower extremities that subsequently leads to leg endothelial dysfunction. We recently conducted a study designed to prevent the reduction in leg blood flow and thus shear stress during prolonged sitting with local heating of the foot (20).…”

“…Sample volume was adjusted to encompass the entire lumen of the vessel without extending beyond the walls, and the cursor was set at midvessel. Popliteal artery FMD was assessed in both legs in the supine position as previously described (2,19,20). Briefly, a rapid inflating cuff was placed on the lower leg.…”

“…Indeed, studies in cultured endothelial cells as well as in vivo studies in animals and humans demonstrate that low shear stress impairs endothelial function and instigates atherosclerosis (4,9,10,16,22,24,27). Notably, arteries of the lower limbs are exposed to marked reductions in blood flow and shear stress during sitting, and this in turn leads to transient endothelial dysfunction (15,19,20,25). Consistent with the notion that sitting-induced leg endothelial dysfunction is mediated by a reduction in shear stress, we recently found that preventing the reduction of shear stress during prolonged sitting using local heating to increase blood flow abolished the impairment in popliteal artery endothelial function (20).…”

Determinants of microvascular function in individuals with and without type 2 diabetes

“…Second, habitual sedentary time was not associated with skin microvascular function. This may be explained by frequent transient interruptions of habitual sedentary behavior by walking and/or standing, in such a way that detrimental effects did not appear 87,88 . Such interruptions have also been shown to be beneficial for cardiovascular risk 89 .…”