The microcirculation: master in normal pregnancy, puppet in preeclampsia

The microcirculation is studied sparsely in the field of maternal hemodynamics. With nailfold video capillaroscopy, further insight is possible in this interesting field within maternal hemodynamics.

This study aimed to investigate the association between functional parameters of the microcirculation and the systemic cardiovascular system in pregnant women at risk for gestational hypertension disorders.

For this observational study, women with high cardiovascular risk according to maternal anthropometrics and obstetrical and medical history were recruited at random gestational ages, depending on the time of referral to the outpatient clinic for high-risk prenatal care at Ziekenhuis Oost-Limburg, Genk, Belgium. After birth, data on maternal and neonatal outcomes were obtained from hospital records, and only women with normal pregnancy (n=142) and preeclampsia (n=34) were included in this analysis. Nailfold video capillaroscopy measurements were performed in the first, second, and/or third trimesters. Video magnification of 200× was used for all fingers except the thumbs, and the stored images were analyzed offline. Capillary density was quantified (n/mm²), mean capillary diameter measured (μm), and capillary bed surface calculated as density × diameter. Cardiac output and total peripheral resistance were measured using impedance cardiography, together with sphygmomanometric blood pressure measurement. A linear mixed model for repeated measures was used to investigate the association between the microvascular and macrovascular parameters. No corrections for multiple testing were applied.

In normal pregnancies, a positive association was observed between the capillary bed surface and total vascular resistance (1.807; P=.01) and a negative association between capillary density and cardiac output (-0.269; P=.037). In preeclampsia, a negative association was observed between capillary density and mean arterial pressure (-0.5649; P=.010), and between capillary diameter and cardiac output (-0.165; P=.032).

The finding of a reduction in capillary density with an increase in blood pressure in preeclampsia is similar to observations in chronic hypertension. This is considered to be the result of capillary closure after the constriction of the precapillary arterioles. However, in normal pregnancy, the increase in capillary bed surface with rising vascular resistance can only be explained by the primary role of microcirculation in preventing capillary overflow via stimulation of arteriolar constriction. These observations elucidate the earliest hemodynamic origins of hypertension at the microcirculatory level in preeclampsia.