The effect of oral antioxidants on brachial artery flow-mediated dilation following 5 and 10 min of ischemia

In light of the current methodological developments in flow-mediated dilation (FMD) testing and the recognition that oxidative stress may play an important role in regulating this process, the present study sought to: (1) compare flow-mediated dilation (FMD) following 5 and 10 min of forearm cuff occlusion, and (2) evaluate the role of oxidative stress on vasodilation, both distal and proximal to the cuff. Of the 14 subjects studied, 6 partook solely in a validation study of the antioxidant cocktail (AOC; vitamins C, E, and α-lipoic acid), while the remaining 8 subjects underwent FMD assessment in response to 5 and 10 min of forearm occlusion following ingestion of AOC or placebo. Although the efficacy of the AOC was clearly documented by elevated plasma ascorbate levels (~95%) and a reduced free radical concentration (~65%), no effects of acute oral antioxidants were observed. FMD was significantly augmented in response to 10 min of forearm occlusion when compared to 5 min, whether expressed as % change (10.1 ± 2 vs. 4.5 ± 1%, respectively) or absolute change in diameter (0.035 ± 0.005 vs. 0.018 ± 0.005 cm, respectively). Additionally, post-occlusion shear rate (28,640 ± 2,799 vs. 18,629 ± 1,724/s, AUC), FMD/shear rate (~50%), and time to peak dilation (68 ± 7 vs. 53 ± 8 s) were greater following 10 min of occlusion. In contrast to previous studies, this investigation has identified a greater brachial artery FMD in response to 10 versus 5 min of forearm ischemia, which appears to be unexplained by oxidative stress.