Flow-Mediated Dilation Decreases in Women, but not Men, Following Mild Acute Intermittent Hypoxia.

Acute, intermittent exposure to mild hypoxia increases sympathetic nervous system activity, decreases arterial shear rate, and increases blood pressure (BP) in young men. Given the BP raising effects of intermittent hypoxia (IH) are less evident in young women, we sought to examine the influence of sex on macro- and microvascular function following IH. BP, macrovascular function (brachial artery flow-mediated dilation [FMD]), microvascular function (reactive hyperemia area under the curve [RHAUC]), and brachial artery shear rate (shear rate area under the curve [SRAUC]) were measured before and following 30 minutes of IH in 18 young adults (8 women, 23±5y). IH elicited an average nadir blood oxygen saturation (SpO) of 92±3% (p<0.0001 vs baseline). In men, brachial systolic (bSBP; 116±6 to 122±7 mmHg, p=0.001) and diastolic (bDBP; 116±6 to 122±7 mmHg, p=0.001) BPs increased from baseline following IH. bSBP (110±8 to 111±7 mmHg, p=0.67) and bDBP (64±7 to 68±7 mmHg, p=0.12) were unchanged in women after IH. Men maintained macrovascular function after IH (ΔFMD: 0.75±2.44%) while women exhibited a decline (ΔFMD: -3.09±2.64%, p=0.006 vs men). Microvascular function and shear rate declined following IH independent of sex (RHAUC: 597±306 to 467±205ml/min, p=0.049; SRAUC: 1772±907 to 1439±596s, p=0.040). Acute mild IH increases BP in healthy men, but not women. In women, both micro- and macrovascular function are lower following acute mild IH; in contrast, only micro-vascular function is lower in men. The sex-specific effects of IH on BP and macrovascular function may have important implications for potential beneficial effects of IH.