Flow-mediated dilatation of the brachial artery in pregnancy at high altitude

Abstract

Objective Pregnancy at high altitude has been associated with increased prevalence of pre-eclampsia and reduced maternal oestrogen levels, factors that have been associated with endothelial dysfunction. The aim of this study was to examine the effect of high altitude (4370 m above sea level) on endothelial function during pregnancy as assessed by a non-invasive method. Design Cross-sectional study.Setting Two maternity units providing routine antenatal care: one at high altitude (District General Hospital -IPSS in Cerro de Pasco, Peru) and one at sea level (Instituto Materno-Perinatal in Lima, Peru). Population Sixty pregnant women at 6 -42 weeks of gestation resident at high altitude (Cerro de Pasco, Peru, 4370 m above sea level) and 54 at sea level (Lima, Peru). Comparisons were performed also in 11 and 14 non-pregnant women at each altitude, respectively. Methods Endothelial function was assessed by flow-mediated dilatation of the brachial artery using highresolution ultrasound. Main outcome measures Differences in flow mediated dilatation of the brachial artery in two groups of pregnant women, one at high altitude and one at sea level. Results Both at high altitude and sea level flow-mediated dilatation of the brachial artery increased in the first two trimesters to levels 32% higher than non-pregnant controls. However, in the third trimester, flowmediated dilatation of the brachial artery was lower than non-pregnant levels. Resting vessel size increased during pregnancy by 15% compared with non-pregnant controls at term, with no difference between the two populations at high and low altitude. Pregnancy at high altitude, compared with sea level, was associated with 59% lower baseline blood flow and 76% higher reactive hyperaemia. Similarly, non-pregnant controls at high altitude compared with sea level demonstrated similar flow-mediated dilatation of the brachial artery and 40% lower resting blood flow of the brachial artery. However, the difference in reactive hyperaemia did not reach statistical significance. Conclusion These data suggest that, during pregnancy at high altitude, endothelial function, as assessed by flow-mediated dilatation of the brachial artery, is not impaired.

Acute dietary nitrate supplementation improves arterial endothelial function at high altitude: A double-blinded randomized controlled cross over study

“…However, no significant changes in velocity of blood flow during rest were found in this study. This is similar to previous findings for velocity of blood flow, however is in contrast to volumetric blood flow (mL$min À1 ) that is reported as decreased in the brachial artery at HA, compared to both measurements at sea level and at 1310 m [1,47].…”

Greater uterine artery blood flow during pregnancy in multigenerational (Andean) than shorter-term (European) high-altitude residents

“…The Andean women's lower blood pressures and calculated uterine vascular resistances at week 36 were consistent with a reduction in afterload. Lower blood pressures and greater flow-induced systemic vasodilation has been observed previously in long-compared with shorter-term high-altitude residents (18,36), as well as in pregnant high-compared with low-altitude Andeans, perhaps due to greater nitric oxide production (13). Viewed conversely, the Europeans' CI flows may also have been limited by relative systemic vasoconstriction resulting from greater sympathetic activity, as suggested by their higher heart rates.…”

The impact of hypoxaemia on vascular function in lowlanders and high altitude indigenous populations

“…Pregnant Andean highlanders have lower blood viscosity and haematocrit compared to non‐pregnant female Andeans (Kametas et al . , ), and do not present impairments in endothelial function during pregnancy. These data indicate that in healthy Andean highlanders, endothelial function does not appear compromised by hypobaric hypoxia; however, more work is required to determine this since the authors of these studies did not control or correct for between‐group differences in shear stress stimuli.…”