The relationship between shear rate and flow-mediated dilation is altered by acute exercise

Endothelial function is a predictor of cardiovascular health and is improved with exercise training. However, it is not clear how exercise acutely affects endothelial function. Previous studies present conflicting results, resulting from varied exercise protocols and ambiguity in data analysis after exercise. The aims of this study were to compare brachial artery endothelial function at rest and post-exercise in and to compare the data expressed as a percent change and normalized to shear rate (SR).

Fifteen young, healthy subjects completed flow-mediated dilation (FMD) tests at rest and immediately after a continuous 30-min treadmill exercise session. Flow-mediated dilation was calculated as percent change in diameter and also normalized for SR.

Flow-mediated dilation was reduced after exercise (8.9 ± 4.3 to 5.8 ± 3.9%, P<0.05), but normalizing for SR nullified this difference (3.6 × 10(-4) ± 1.8 × 10(-4) to 2.7 × 10(-4) ± 2.4 × 10(-4) %, P=0.25). Baseline SR was significantly greater after exercise than at rest (224 ± 72 to 354 ± 158 s(-1) , P<0.05). Baseline diameter, time to peak diameter, and SR area under the curve were not different between the two conditions. The relationship between SR and FMD was strong at rest (r=0.82, P<0.001), but weak post-exercise (r=0.16, P=0.6).

The weak relationship in FMD and SR after exercise suggests that these data should not be normalized following aerobic exercise. Thus, endothelial function was attenuated after a continuous 30-min aerobic exercise session.