Macrovascular Function Preserved In Men, But Not Women, Following Acute Intermittent Hypoxia

Acute, intermittent exposure to hypoxia increases sympathetic nervous system activity and blood pressure in young, healthy men. Similarly, arterial shear rate increases during intermittent hypoxia (IH) but falls below baseline levels afterward. Given the blood pressure raising effects of IH are less evident in young, healthy women, we sought to examine the influence of sex on macro- and microvascular responses to IH. PURPOSE: To evaluate macro- and microvascular function before and after acute IH in young, healthy men and women. METHODS: Blood pressure, macrovascular function (brachial artery flow-mediated dilation [FMD]), and microvascular function (reactive hyperemia area under the curve [RH AUC]) were measured before and 30 minutes after acute IH in 18 young, healthy adults (10 M/8F, 23 ± 5y). Acute IH consisted of 16 cycles of breathing 25 seconds (s) of low oxygen (5%) air followed by 90s of room air (30 minutes total). Sex-related differences in the effect of IH on main outcome variables were assessed via 2-way repeated measures ANOVA. Absolute changes from baseline values were compared between the sexes via unpaired t-tests. RESULTS: During IH, all participants achieved an average nadir blood oxygen saturation (SpO2) of 92% (p < 0.0001 as compared to resting SpO2). In men, brachial systolic (bSBP) and diastolic blood pressures (bDBP) increased from baseline following IH (bSBP: 116 ± 6 to 122 ± 7 mmHg, p = 0.001; bDBP: 64 ± 8 to 71 ± 8 mmHg, p = 0.003). However, bSBP and bDBP were unchanged in women after IH (bSBP: 110 ± 8 to 111 ± 7 mmHg, p = 0.67; bDBP: 64 ± 7 to 68 ± 7 mmHg p = 0.12). While men maintained macrovascular function after IH (ΔFMD: 0.75 ± 2.44%), women exhibited a significant decline (ΔFMD: -3.09 ± 2.64% ; p = 0.006 as compared to men). All participants exhibited a decline in microvascular function following IH, independent of sex (RHAUC: 35847 ± 18334 to 28039 ± 12284; p = 0.049). CONCLUSION: Present data confirm the blood pressure raising effects of IH are observed primarily in men. Despite this, macrovascular function is preserved in men, yet reduced in women, following exposure to acute IH. These data highlight the potentially beneficial role of blood pressure and shear rate increases on macrovascular function during hypoxia, particularly in men.