Normal human pregnancy requires a dramatic increase in uteroplacental blood flow which is achieved by a transformation in the geometry of uterine spiral arteries, a key element in this blood supply system. The transformation is mediated by trophoblast invasion directed at converting a portion of the spiral artery into an open funnel, thereby greatly reducing resistance to flow. The converted portion lies within the depth of the decidua and part of the myometrium. Insufficient depth of trophoblast invasion in early pregnancy predisposes to inadequate perfusion of the developing placenta andfetus and may lead to preeclampsia, fetal growth restriction and preterm delivery, sometimes referred to as the "Great Obstetrical Syndromes". We examine the hemodynamic consequences of spiral artery transformation in human pregnancy and the relationship between the degree of transformation and the corresponding change in flow rate and resistance to flow. We identify two key variables in determining the hemodynamic change: the longitudinal converted fraction of the spiral artery and the relative downstream diameterof the open funnel. Our results indicate that there is a critical threshold in the value of the converted fraction required to achieve the marked increase in uteroplacental blood flow in normal pregnancy. This finding validates common clinical observations that the depth of trophoblast invasion reflects the "adequacy" of the increase in uteroplacental blood supply required in normal human pregnancy. Our results provide a quantitative measure of that adequacy and may serve as a future diagnostic marker for high-risk pregnancy.

中文翻译：

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人体妊娠中不完全的子宫螺旋动脉转化的血流动力学后果，对胎盘功能障碍和先兆子痫的影响。

正常人的怀孕需要子宫胎盘血流量的急剧增加，这是通过改变子宫螺旋动脉的几何形状来实现的，子宫螺旋动脉是血液供应系统中的关键要素。转化是由滋养细胞入侵介导的，该滋养细胞入侵旨在将一部分螺旋动脉转化为开放漏斗，从而大大降低了流动阻力。转化的部分位于蜕膜的深度和子宫肌层的一部分内。妊娠早期滋养细胞的浸润深度不足，容易导致发育中的胎盘和胎儿的灌注不足，并可能导致先兆子痫，胎儿生长受限和早产，有时被称为“大产科综合症”。我们检查了人类妊娠中螺旋动脉转化的血液动力学后果，以及转化程度与相应的流速变化和流动阻力之间的关系。我们确定了确定血液动力学变化的两个关键变量：螺旋动脉的纵向转换分数和开放漏斗的相对下游直径。我们的结果表明，正常妊娠中实现胎盘胎盘血流量显着增加所需的转换分数的值存在一个临界阈值。这一发现证实了常见的临床观察结果，即滋养层细胞浸润的深度反映了正常人妊娠所需子宫胎盘血液供应增加的“充分性”。