Pennati G, Bellotti M, De Gasperi C, Rognoni G
Laboratory of Mechanics of Biological Structures, Department of Bioengineering, Politecnico di Milano University of Milan, Milan, Italy.
Ultrasound Obstet Gynecol. 2004 Feb;23(2):131-7. doi: 10.1002/uog.938.
Several studies have assumed a parabolic velocity profile through the umbilical vein (UV) to derive the mean spatial velocity that is indispensable for flow rate calculations. However, the structure and arrangement of the umbilical cord suggest that velocity profiles may vary. The aim of this study was to evaluate UV spatial flow velocity profiles at different sites along the umbilical cord.
Ten singleton pregnancies with a gestational age between 26 and 34 weeks were included in the study. Ultrasound equipment with an inbuilt function for analysis of the spatial velocity profile along a line located in a fixed plane was used to obtain UV velocity profiles. Velocity profiles were obtained at the placental insertion and in a free intra-amniotic loop of the cord. Two-dimensional (2D) velocity distribution coefficients were evaluated as ratios between mean and maximum velocities along the investigated lines.
2D velocity distribution coefficients at the placental insertion (0.85 +/- 0.03) were significantly higher (P < 0.00001) than those obtained from a free loop of cord (0.76 +/- 0.03). Values indicated that velocity profiles are approximately flat at the placental insertion and become more parabolic moving downstream. Moreover, profiles become skewed in association with cord curvature and show peculiar biphasic shapes immediately downstream from the placenta.
Flow velocity profiles in the UV are not perfectly parabolic and modify along the cord. These characteristics may affect the evaluation of UV blood flow rate.
多项研究假定脐静脉（UV）内的速度分布呈抛物线形，以推导流量计算中不可或缺的平均空间速度。然而，脐带的结构和排列表明速度分布可能存在差异。本研究的目的是评估沿脐带不同部位的脐静脉空间流速分布。
本研究纳入了10例单胎妊娠，孕周在26至34周之间。使用具有沿固定平面内一条线分析空间速度分布功能的超声设备来获取脐静脉速度分布。在胎盘附着处和脐带的羊膜腔内游离段获取速度分布。二维（2D）速度分布系数被评估为沿研究线的平均速度与最大速度之比。
胎盘附着处的二维速度分布系数（0.85±0.03）显著高于脐带游离段（0.76±0.03）（P<0.00001）。这些值表明，在胎盘附着处速度分布近似平坦，向下游移动时变得更呈抛物线形。此外，速度分布会随着脐带弯曲而出现偏斜，并在胎盘下游紧邻处呈现出特殊的双相形状。
脐静脉内的流速分布并非完美的抛物线形，且沿脐带会发生变化。这些特征可能会影响对脐静脉血流速度的评估。
