Effect of acute changes in oxygen tension on flow-mediated dilation. Relation to cardiovascular risk

Objective. Oxygen-dependent changes in vascular diameters may be detrimental when the endothelium is dysfunctional. Design. Endothelial responsiveness was evaluated by brachial ultrasound and flow-mediated/nitroglycerin-mediated dilation (FMD/NMD). FMD/NMD was investigated in males with increased risk of cardiovascular disease (mean age 44 +/- 2 years, n =10) and matched controls without risk factors (44 +/- 2 years, n =10). FMD/NMD was assessed during normoxia (21% O-2, 79% N-2), while inhaling hypoxic gas (12.5% O-2, FMDHyp/NMD), and 100% O-2 supplementation (FMDO2/NMD). In a second study we addressed the effect of lipid lowering. Twenty persons with cardiovascular risk (mean age 50 +/- 2 years) were treated with atorvastatin (80 mg/day) and FMD/NMD was measured during normoxia, hypoxia and oxygen supplementation before, after 1 day and 3 months. Results. Oxygen supplementation evoked vasoconstriction, while FMDHyp/NMD was reduced compared to FMD/NMD. Atorvastatin significantly lowered total cholesterol, LDL cholesterol, and ADMA after 1 day of treatment, while triglycerides, ApoB and hsCRP were lowered after 3 months. Atorvastatin did not change FMD/NMD irrespective of oxygen tension. Conclusion. Irrespective of risk factors or atorvastatin, hypoxia reduced endothelial vasodilation while oxygen supplementation evoked vasoconstriction.