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

Area of Science:

• Cardiovascular physiology
• Vascular biology
• Sex differences in health

Background:

• Sex disparities in cardiovascular disease are established, yet the underlying vascular mechanisms require further elucidation.
• Understanding vascular reactivity differences between young males and females is crucial for identifying early risk factors.

Purpose of the Study:

• To investigate sex-based differences in macrovascular and microvascular reactivity in young, healthy adults.
• To compare flow-mediated dilation (FMD) and post-occlusive reactive hyperemia (PORH) between young males and females.

Main Methods:

• A systematic meta-analysis of studies measuring FMD or PORH using ultrasound or laser Doppler in individuals under 40 years old and with a BMI under 30.
• Quantitative analysis of baseline artery diameter, FMD, wall shear rate (WSR), blood flow changes (ΔBF), and time-to-peak (TTP).
• Random-effects modeling was employed, with sex as a predictor and age and BMI as moderators.

Main Results:

• Across 51 studies (2426 subjects), females showed smaller baseline artery diameter and time-to-peak but higher FMD and WSR compared to males, without adjustment for age/BMI.
• After adjustment for age and BMI, and including studies with forearm occlusion, significant FMD differences between sexes were no longer observed.
• No significant sex differences were found in brachial artery or microcirculation blood flow changes (ΔBF, microΔBF).

Conclusions:

• Young females consistently demonstrate higher WSR than males, but evidence for superior FMD after forearm occlusion is not conclusive.
• Statistically significant enhanced vascular reactivity in the microcirculation of young females could not be confirmed.
• The findings suggest nuanced sex differences in vascular reactivity, with WSR being a key differentiator, while FMD and microvascular responses require further investigation.