The Impact of Chronic E-Cigarette Use on Flow- Mediated Dilation Elicited by a Sustained Shear Stress Stimulus

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Curd, Evan D.
E-Cigarette , Endothelial Function , Flow Mediated Dilation
E-cigarettes, are popular electronic nicotine delivery devices. Acute human, animal and in-vitro models of e-cigarette exposure, have identified significant impairments in vascular endothelial cell (EC) function. The endothelium is a single layer of cells lining the arteries and is crucial to the regulation of vascular health and function, and impairments are known to increase risk for cardiovascular disease. ECs are stimulated by increases in blood flow-associated forces on the arterial walls (known as shear stress), which cause dilation. The standard test of endothelial function in humans involves creating a transient increase in blood flow in a large artery and measuring the endothelial dependent dilation, this is known as reactive hyperemia flow-mediated dilation (RH-FMD). Three previous studies have assessed the impact of chronic e-cigarette use on human endothelial function all using RH-FMD, with only one finding a significant impairment between users and controls. Endothelial function can also be tested by creating sustained increases in blood flow with handgrip exercise, known as sustained stimulus FMD (SS-FMD). There is evidence suggesting that SS-FMD may detect endothelial dysfunction missed by the standard RH-FMD test. The impact of chronic e-cigarette use on SS-FMD has never been investigated. It was hypothesized that e-cigarette users would display significant impairments in endothelial function assessed by SS-FMD regardless of what is observed for RH-FMD. Ten participants were recruited (4 e-cigarette users, 19 ±1 years; 6 control, 21 ± 2 [mean ± SD]) and participated in two laboratory visits in which the endothelial function of the brachial artery was assessed by both RH- and SS-FMD. Data are [mean ± SD]. RH-FMD was significantly impaired in the e-cigarette group (5.25 ± 1.3%, control: 8.85 ± 3.6%; p=0.010). Similarly, SS-FMD was also lower in e-cigarette users, however, while this was a large effect size the difference between groups did not reach significance (e-cigarettes: 5.99 ± 2.61, control 8.54 ± 3.51; p=0.268; Cohen’s d: 0.82). These results suggest that chronic e-cigarette use has the potential to cause endothelial dysfunction when assessed with standard (RH-FMD) and handgrip exercise (SS-FMD) tests. Contrary to our hypothesis, the SS-FMD test appears not to be a more sensitive detector of e- cigarette induced endothelial dysfunction.
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