Acute impact of retrograde shear rate on brachial and superficial femoral artery flow-mediated dilation in humans

Abstract

Retrograde shear rate (SR) in the brachial artery (BA) is associated with endothelial dysfunction; a precursor to atherosclerosis. The BA does not typically manifest clinical atherosclerosis, whereas the superficial femoral artery (SFA) is more prone to developing plaque. Examine whether the impact of incremental levels of retrograde SR differs between atherosclerosis‐prone (i.e., SFA) and ‐resistant vessels (i.e., BA) in healthy men. Thirteen healthy young men reported three times to the laboratory. We examined BA flow‐mediated dilation (FMD) before and after 30‐min exposure to cuff inflation around the forearm at 0, 30, and 60 mmHg, to manipulate retrograde SR. Subsequently, the 30‐min intervention was repeated in the SFA, using the same cuff pressure as in the forearm. Order of testing (vessel and intervention) was randomized among subjects. We found a dose‐dependent increase in retrograde SR with 30 and 60 mmHg cuff inflation, which was present in both the BA and SFA (all P < 0.05). BA and SFA FMD decreased after the 30‐min intervention (“time”: P = 0.012), and this was dependent on cuff pressure (“cuff × time”: P = 0.024). A significant decrease in FMD was observed after 60 mmHg only and this change was similarly present in both arteries (“time × artery”: P = 0.227). Moreover, the BA and SFA demonstrate a similar relationship between changes in retrograde SR and FMD (r = 0.498 and 0.475, respectively). Our study demonstrates that acute exposure to an increase in retrograde shear leads to comparable decreases in FMD in atherosclerotic‐prone and ‐resistant conduit arteries in humans.

Impact of 2‐Weeks Continuous Increase in Retrograde Shear Stress on Brachial Artery Vasomotor Function in Young and Older Men

“…In this manner, this study successfully introduced compression sleeves as a method to manipulate retrograde SR, both acutely and chronically in men in vivo. Although a nonsignificant increase was found in antegrade SR in both young and older men, the main observation was that we (in line with our previous work) successfully manipulated retrograde shear 2, 12, 39. Although we only explored the impact of the sleeve intervention on resting levels of retrograde shear, we are confident that increased levels of retrograde SR were also present during various activities of daily living.…”

“…In previous studies, we used pneumatic cuffs to manipulate retrograde shear acutely 2, 12. For chronic shear manipulation, however, blood pressure cuffs are impractical.…”

“…In contrast, elevation in retrograde shear stress may be potentially detrimental 2, 10, 11. For example, an inverse and dose‐dependent relationship is described between acute increases in retrograde shear rate (SR) and brachial artery endothelial function in young men 2, 12…”

Influence of sympathetic vasoconstrictor tone on conduit artery retrograde and oscillatory shear: Effects of habitual aerobic exercise in middle-aged and older adults

“…Conduit artery shear rate patterns are affected by downstream vascular resistance 2,11,12) . Previous research has demonstrated that acute elevations in vascular resistance that occur via an increase in muscle sympathetic nerve activity (MSNA) with lower body negative pressure (LBNP) are associated with an increase in conduit artery retrograde and oscillatory shear 12) Moreover, Casey et al reported that α-adrenergic vasoconstriction of the downstream resistance vessels is a major contributor to agerelated increases in conduit arteries retrograde and oscillatory shear at rest 8) .…”

“…Shear stress demonstrates a typical pattern (i.e., antegrade and retrograde shear) in conduit arteries. Elevation in retrograde and oscillatory shear may have pro-atherogenic effects [1][2][3][4][5][6] . Aging causes increased retrograde shear and oscillatory shear in peripheral conduit arteries [7][8][9][10] .…”