A valve mechanism for artery motion to drive cerebrospinal fluid into brain tissue

Metabolic waste is cleared from the brain in part by the flow of cerebrospinal fluid (CSF) fluid through perivascular spaces (PVSs) that surround blood vessels. Experiments show that global oscillations in vessel diameter increase CSF inflow. How those oscillations cause net flow into -- not out of -- brain tissue is not well understood, however. A valve mechanism is needed, but no valves are found inside the PVS space. We hypothesize that the gaps in the outer PVS boundary change size as pressure varies, altering tissue permeability and functioning like valves. Simulating flow driven by vessel wall motion in the presence of pressure-dependent permeability, we found that inflow can be promoted over outflow. We will discuss the range of parameters that allow valve-like action and their relevance to the real brain.