Glenny R W, Robertson H T
Department of Medicine, University of Washington, Seattle 98195, USA.
J Appl Physiol (1985). 1995 Jul;79(1):357-69. doi: 10.1152/jappl.1995.79.1.357.
Pulmonary perfusion is spatially correlated with neighboring regions of lung having similar magnitudes of flow and distant pieces exhibiting negative correlation. Although local correlation has been noted in a wide variety of natural processes, negative correlation has not and it may be unique to organ blood flow. We investigate the regional perfusion predicted by a three-dimensional branching vascular model to determine whether such a model can create negative correlation of perfusion. The distribution of flows is modeled by a dichotomously branching tree in which the fraction of flow from parent to daughter branches is gamma and 1-gamma at each bifurcation. The flow asymmetry parameter (gamma) is randomly chosen for each bifurcation from a normal distribution with a mean of 0.5 with an SD of sigma. The branches branch along one of three orthogonal directions to assure a space-filling structure. This model produces flow distributions similar to those observed in experimental animals, with perfusion being positively correlated locally and negatively correlated at distance. The model is refined by incorporating an effect of gravity, which redirects a fraction (delta), of the flow against gravity to the companion daughter branch in the gravitational direction. A flow bias in the "dorsal" direction is also introduced to account for differences in supine-prone perfusion gradients. In its final form, this three-dimensional branching model accounts for previously observed 1) spatial correlation of regional perfusion with negative correlation over distance, 2) isogravitational perfusion heterogeneity, 3) differences in supine and prone perfusion gradients, 4) positive correlation of flows between supine and prone postures, 5) relatively small contributions of gravity to perfusion heterogeneity, and 6) fractal distributions of flow. This three-dimensional branching vascular model relates the function and structure of the pulmonary vascular tree, offering an explanation for both heterogeneous and spatially correlated regional flows.
肺灌注与肺的相邻区域在空间上相关，这些相邻区域具有相似的血流大小，而远处的区域则呈现负相关。尽管在各种各样的自然过程中都已注意到局部相关性，但负相关性尚未被发现，它可能是器官血流所特有的。我们研究了三维分支血管模型预测的区域灌注，以确定这样的模型是否能产生灌注的负相关性。血流分布由二叉分支树建模，在每个分支点，从父分支到子分支的血流分数分别为γ和1 - γ。每个分支点的血流不对称参数（γ）从均值为0.5、标准差为σ的正态分布中随机选取。分支沿着三个正交方向之一进行分支，以确保形成空间填充结构。该模型产生的血流分布与实验动物中观察到的相似，灌注在局部呈正相关，在远处呈负相关。通过纳入重力效应来改进该模型，重力效应会使一部分血流（δ）逆着重力方向流向重力方向的伴随子分支。还引入了“背侧”方向的血流偏向，以解释仰卧位和俯卧位灌注梯度的差异。在其最终形式中，这个三维分支模型解释了先前观察到的1）区域灌注的空间相关性以及远距离的负相关性，2）等重力灌注异质性，3）仰卧位和俯卧位灌注梯度的差异，4）仰卧位和俯卧位姿势之间血流的正相关性，5）重力对灌注异质性的贡献相对较小，以及6）血流的分形分布。这个三维分支血管模型将肺血管树的功能和结构联系起来，为不均匀且空间相关的区域血流提供了解释。
