The brain lacks a conventional lymphatic system to remove metabolic waste. It has been proposed that directional fluid movement through the arteriolar paravascular space (PVS) promotes metabolite clearance. We performed simulations to examine if arteriolar pulsations and dilations can drive directional CSF flow in the PVS and found that arteriolar wall movements do not drive directional CSF flow. We propose an alternative method of metabolite clearance from the PVS, namely fluid exchange between the PVS and the subarachnoid space (SAS). In simulations with compliant brain tissue, arteriolar pulsations did not drive appreciable fluid exchange between the PVS and the SAS. However, when the arteriole dilated, as seen during functional hyperemia, there was a marked exchange of fluid. Simulations suggest that functional hyperemia may serve to increase metabolite clearance from the PVS. We measured blood vessels and brain tissue displacement simultaneously in awake, head-fixed mice using two-photon microscopy. These measurements showed that brain deforms in response to pressure changes in PVS, consistent with our simulations. Our results show that the deformability of the brain tissue needs to be accounted for when studying fluid flow and metabolite transport.

中文翻译：

---

功能性充血驱动血管旁间隙的液体交换

大脑缺乏传统的淋巴系统来清除代谢废物。有人提出，通过小动脉血管旁间隙（PVS）的定向液体运动可促进代谢物清除。我们进行了模拟来检查小动脉搏动和扩张是否可以驱动 PVS 中的定向 CSF 流动，并发现小动脉壁运动不会驱动定向 CSF 流动。我们提出了一种从 PVS 清除代谢物的替代方法，即 PVS 和蛛网膜下腔 (SAS) 之间的液体交换。在顺应性脑组织的模拟中，小动脉搏动并没有驱动 PVS 和 SAS 之间明显的液体交换。然而，当小动脉扩张时，如功能性充血期间所见，会出现明显的液体交换。模拟表明功能性充血可能有助于增加 PVS 的代谢物清除率。我们使用双光子显微镜同时测量了清醒、头部固定的小鼠的血管和脑组织位移。这些测量结果表明，大脑会因 PVS 中的压力变化而发生变形，这与我们的模拟结果一致。我们的结果表明，在研究液体流动和代谢物运输时需要考虑脑组织的变形性。