Schmid Franca, Reichold Johannes, Weber Bruno, Jenny Patrick
Institute of Fluid Dynamics, ETH Zurich, Zurich, Switzerland; and
Institute of Fluid Dynamics, ETH Zurich, Zurich, Switzerland; and.
Am J Physiol Heart Circ Physiol. 2015 Apr 1;308(7):H733-42. doi: 10.1152/ajpheart.00335.2014. Epub 2015 Jan 23.
Recent studies suggest that pericytes around capillaries are contractile and able to alter the diameter of capillaries. To investigate the effects of capillary dilation on network dynamics, we performed simulations in artificial capillary networks of different sizes and complexities. The unequal partition of hematocrit at diverging bifurcations was modeled by assuming that each red blood cell (RBC) enters the branch with the faster instantaneous flow. Network simulations with and without RBCs were performed to investigate the effect of local dilations. The results showed that the increase in flow rate due to capillary dilation was less when the effects of RBCs are included. For bifurcations with sufficient RBCs in the parent vessel and nearly equal flows in the branches, the flow rate in the dilated branch did not increase. Instead, a self-regulation of flow was observed due to accumulation of RBCs in the dilated capillary. A parametric study was performed to examine the dependence on initial capillary diameter, dilation factor, and tube hematocrit. Furthermore, the conditions needed for an efficient self-regulation mechanism are discussed. The results support the hypothesis that RBCs play a significant role for the fluid dynamics in capillary networks and that it is crucial to consider the blood flow rate and the distribution of RBCs to understand the supply of oxygen in the vasculature. Furthermore, our results suggest that capillary dilation/constriction offers the potential of being an efficient mechanism to alter the distribution of RBCs locally and hence could be important for the local regulation of oxygen delivery.
最近的研究表明，毛细血管周围的周细胞具有收缩性，能够改变毛细血管的直径。为了研究毛细血管扩张对网络动力学的影响，我们在不同大小和复杂度的人工毛细血管网络中进行了模拟。通过假设每个红细胞（RBC）以更快的瞬时流速进入分支，对分叉处血细胞比容的不均等分配进行了建模。进行了有无红细胞的网络模拟，以研究局部扩张的影响。结果表明，当考虑红细胞的影响时，由于毛细血管扩张导致的流速增加较小。对于母血管中有足够红细胞且分支中流量几乎相等的分叉，扩张分支中的流速并未增加。相反，由于红细胞在扩张的毛细血管中积累，观察到了流量的自我调节。进行了参数研究，以检验对初始毛细血管直径、扩张因子和管内血细胞比容的依赖性。此外，还讨论了有效自我调节机制所需的条件。这些结果支持了以下假设：红细胞在毛细血管网络的流体动力学中起重要作用，并且考虑血流速度和红细胞分布对于理解脉管系统中的氧气供应至关重要。此外，我们的结果表明，毛细血管扩张/收缩具有局部改变红细胞分布的潜在有效机制，因此可能对局部氧气输送调节很重要。
