Fluid-dynamic models of the flow of cerebrospinal fluid in the brain have treated the perivascular spaces either as open (without internal solid obstacles) or as porous. Here, we present experimental evidence that pial (surface) periarterial spaces in mice are essentially open. (1) Paths of particles in the perivascular spaces are smooth, as expected for viscous flow in an open vessel, not diffusive, as expected for flow in a porous medium. (2) Time-averaged velocity profiles in periarterial spaces agree closely with theoretical profiles for viscous flow in realistic models, but not with the nearly uniform profiles expected for porous medium. Because these spaces are open, they have much lower hydraulic resistance than if they were porous. To demonstrate, we compute hydraulic resistance for realistic periarterial spaces, both open and porous, and show that the resistance of the porous spaces are greater, typically by a factor of a hundred or more. The open nature of these periarterial spaces allows significantly greater flow rates and more efficient removal of metabolic waste products.

中文翻译：

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小鼠大脑的表面动脉周围空间是开放的，而不是多孔的

脑中脑脊液流动的流体动力学模型将血管周围空间视为开放（没有内部固体障碍）或多孔。在这里，我们提出实验证据表明小鼠的软脑膜（表面）动脉周围空间基本上是开放的。(1) 血管周围空间中颗粒的路径是光滑的，正如开放血管中的粘性流动所预期的那样，而不是多孔介质中流动所预期的扩散。(2) 动脉周围空间的时间平均速度分布与现实模型中粘性流的理论分布非常吻合，但与多孔介质预期的几乎均匀分布不符。因为这些空间是开放的，所以它们的水阻力比多孔的要低得多。为了演示，我们计算了真实动脉周围空间的水阻力，包括开放的和多孔的，并表明多孔空间的阻力更大，通常是一百倍或更多。这些动脉周围空间的开放性质允许显着更大的流速和更有效地去除代谢废物。