Abstract
INTRODUCTION: Whilst the impact of changes in blood flow and shear stress on artery function are well documented, the acute effects of increases in arterial pressure are less well described. The aim of this study was to assess the effect of 30-minutes of elevated blood pressure, in the absence of changes in shear stress or sympathetic nervous system (SNS) activation, on conduit arterial diameter. METHODS: Ten male subjects undertook 3 sessions of 30-minutes unilateral handgrip (HG) exercise at 5, 10 and 15% of maximal voluntary contractile (MVC) strength. Brachial artery shear and flow were measured simultaneously during exercise in the active and contralateral resting, arms. Bilateral brachial artery diameter was simultaneously assessed prior to- and immediately post-exercise. In a second experiment, 6 subjects repeated the 15% MVC condition whilst continuous vascular measurements were collected along with measures of muscle sympathetic nerve activity (MSNA). RESULTS: Unilateral HG exercise at all intensities induced step-wise elevations in blood pressure (P<0.01). Whilst step-wise increases were evident in shear rate in the exercising arm (P<0.001), no changes were apparent in the non-exercising limb (P=0.42). Brachial diameter increased in the exercising arm (P=0.02), but significantly decreased in the non-exercising arm (P=0.03). At 15% MVC, changes in diameter were significantly different between arms (interaction-effect P=0.01), with no significant changes in MSNA. CONCLUSION: Acute increases in transmural pressure, independent of shear and SNS activity, reduce arterial calibre in normotensive humans in vivo. These changes in diameter were mitigated by exercise-induced elevations in shear rate in the active limb.
