Wilke D J, Denier J P, Khong T Y, Mattner T W
School of Mathematical Sciences, The University of Adelaide, Australia.
Department of Mathematics, Macquarie University, Australia.
J Biomech. 2018 Oct 5;79:78-87. doi: 10.1016/j.jbiomech.2018.07.044. Epub 2018 Aug 10.
A fluid dynamic study of blood flow within the umbilical vessels of the human maternal-fetal circulatory system is considered. It is found that the umbilical coiling index (UCI) is unable to distinguish between cords of significantly varying pressure and flow characteristics, which are typically determined by the vessel curvature, torsion and length. Larger scale geometric non-uniformities superposed over the inherent coiling, including cords exhibiting width and/or local UCI variations as well as loose true knots, typically produce a small effect on the total pressure drop. Crucially, this implies that a helical geometry of mean coiling may be used to determine the steady vessel pressure drop through a more complex cord. The presence of vessel constriction, however, drastically increases the steady pressure drop and alters the flow profile. For pulsatile-flow within the arteries, the steady pressure approximates the time-averaged value with high accuracy over a wide range of cords. Furthermore, the relative peak systolic pressure measured over the period is virtually constant and approximately 25% below the equivalent straight-pipe value for a large range of non-straight vessels. Interestingly, this suggests that the presence of vessel helicity dampens extreme pressures within the arterial cycle and may provide another possible evolutionary benefit to the coiled structure of the cord.
本文对人类母胎循环系统脐带血管内的血流进行了流体动力学研究。研究发现，脐带盘绕指数（UCI）无法区分压力和血流特征差异显著的脐带，这些特征通常由血管曲率、扭转和长度决定。叠加在固有盘绕之上的较大尺度几何不均匀性，包括宽度和/或局部UCI变化的脐带以及松散的真结，通常对总压降影响较小。至关重要的是，这意味着平均盘绕的螺旋几何形状可用于确定通过更复杂脐带的稳定血管压降。然而，血管狭窄的存在会大幅增加稳定压降并改变血流分布。对于动脉内的脉动流，在广泛的脐带范围内，稳定压力在高精度下近似于时间平均值。此外，在该时间段内测量的相对收缩压峰值实际上是恒定的，并且在大范围的非直管血管中比等效直管值低约25%。有趣的是，这表明血管螺旋性的存在会抑制动脉周期内的极端压力，并且可能为脐带的盘绕结构提供另一种可能的进化益处。
