Bennett S H, Eldridge M W, Zaghi D, Zaghi S E, Milstein J M, Goetzman B W
Department of Pediatrics, Division of Neonatology, University of California Davis, Davis, California 95616, USA.
Am J Physiol Heart Circ Physiol. 2000 Dec;279(6):H3047-57. doi: 10.1152/ajpheart.2000.279.6.H3047.
Bifurcation is a basic form of vascular connection. It is composed of a parent vessel of diameter d(0), and two daughter vessels, d(1) and d(2), where d(0) > d(1) >/= d(2). Optimal values for the bifurcation area ratio, beta = (d(1)(2) + d(2)(2))/d(0)(2), and the junction exponent, x, in d(0)(x) = d(1)(x) + d(2)(x), are postulated to be universal in nature. However, we have hypothesized that the perinatal pulmonary arterial circulation is an exception. Arterial diameters were measured in pulmonary vascular casts of a fetal lamb (140 days gestation/145 days term) and a neonatal lamb (1 day old). The values for beta and x were evaluated in 10,970 fetal and 846 neonatal bifurcations sampled from the proximal and intermediate arterial regions. Mean values and confidence intervals (CI) for the fetus were beta = 0.890 (0.886-0.895 CI) and x = 1.75 (1.74-1.76 CI); and for the newborn were beta = 0.913 (0.90-0.93 CI) and x = 1. 79 (1.75-1.82 CI). These values are significantly different from Murray's law (beta > 1, x = 3) or the West-Brown-Enquist law (beta = 1, x = 2). Therefore, perinatal pulmonary bifurcation design appears to be distinctive and exceptional. The decreasing cross-sectional area with branching leads to the hemodynamic consequence of shear stress amplification. This structural organization may be important for facilitating vascular development at low flow rates; however, it may be the origin of unstable reactivity if elevated blood flow and pressure occurs.
分叉是血管连接的一种基本形式。它由直径为d(0)的母血管以及两条子血管d(1)和d(2)组成，其中d(0) > d(1) ≥ d(2)。分叉面积比β = (d(1)² + d(2)²)/d(0)²以及d(0)^x = d(1)^x + d(2)^x中的连接指数x的最优值被假定在本质上是通用的。然而，我们推测围产期肺动脉循环是个例外。在一只胎羊（妊娠140天/足月145天）和一只新生羊（1日龄）的肺血管铸型中测量了动脉直径。从近端和中间动脉区域采集了10970个胎儿分叉和846个新生儿分叉，评估了β和x的值。胎儿的平均值和置信区间（CI）为β = 0.890（0.886 - 0.895 CI），x = 1.75（1.74 - 1.76 CI）；新生儿的为β = 0.913（0.90 - 0.93 CI），x = 1.79（1.75 - 1.82 CI）。这些值与默里定律（β > 1，x = 3）或韦斯特 - 布朗 - 恩奎斯特定律（β = 1，x = 2）显著不同。因此，围产期肺部分叉设计似乎是独特且异常的。随着分支而减小的横截面积导致了剪切应力放大的血流动力学后果。这种结构组织对于在低流速下促进血管发育可能很重要；然而，如果出现血流和压力升高，它可能是不稳定反应性的根源。
