Sex differences in macro- and microvascular reactivity - a systematic review and meta-analysis.

Introduction: Sex differences in cardiovascular disease are well recognized, but underlying vascular mechanisms remain unclear. This meta-analysis investigates whether young adult healthy males and females differ in macro- and microvascular reactivity, via flow-mediated dilation (FMD) and post-occlusive reactive hyperemia (PORH). Methods: A systematic search of MEDLINE, Embase, and Central identified eligible studies meeting the criteria: FMD or PORH test assessment; Ultrasound or Laser Doppler was used on the brachial artery or the skin; including both sexes under the mean age of <40 years and a mean BMI of <30. We performed a quantitative analysis for baseline artery diameter (BAD), FMD, wall shear rate (WSR), relative change in blood flow on the brachial artery (ΔBF) and microcirculation (microΔBF), and time-to-peak (TTP). Random-effects model was used for synthesis with sex as a predictor and age and BMI as moderators. Results: A total of 51 eligible articles comprising 2426 subjects were included. Without adjustment for age and BMI (studies: 48), females had smaller BAD and TTP but higher FMD and WSR compared with males. No significant differences were found for ΔBF or microΔBF. After adjustment for age and BMI and inclusion of studies using forearm occlusion (studies: 23), FMD differences between sexes were no longer significant. Conclusion: While WSR was consistently higher in young females than in males, there was no clear evidence that females exhibit higher FMD after forearm occlusion. Likewise, greater vascular reactivity in microcirculation could not be statistically confirmed.