# Dynamics of brain valves: ostensible rectification mechanisms for cerebrospinal fluid flow

## TL;DR

This study explores how astrocyte endfeet might act as valves to control cerebrospinal fluid flow in the brain.

## Contribution

The paper introduces a fluid–structure interaction model to investigate how astrocyte endfeet could rectify oscillatory CSF flow.

## Key findings

- Astrocyte endfeet can rectify CSF flow at frequencies linked to brain activity and respiration.
- Three idealized geometric arrangements of endfeet gaps were found to effectively rectify fluid flow.
- Oscillatory pressures can drive net CSF flow through these modeled valve-like structures.

## Abstract

The flow of cerebrospinal fluid (CSF) through perivascular spaces (PVSs) is an important part of the brain’s system for clearing metabolic waste. Astrocyte endfeet ensheath the PVSs of penetrating arteries, separating them from brain extracellular space (ECS). Gaps between astrocyte endfeet could provide a low-resistance pathway for fluid transport across the endfoot wall. Recent research suggests that the astrocyte endfeet may also function as valves that rectify the CSF flow, allowing oscillatory pressures to drive net flows like those observed in experiments. In this study, we employ fluid–structure interaction modelling to investigate the endfoot valve mechanism. Due to the unavailability of precise in vivo measurements of gap shape and size, we explore three possible, though idealized, geometric arrangements: wedge-shaped gaps, overlapping endfeet of different sizes and curvature of the endfoot wall. For each, we quantify the dependence of net flow on oscillatory pressure amplitude, frequency and other key parameters. For all three, our simulations demonstrate effective flow rectification at frequencies associated with functional hyperaemia, respiration and cardiac pulsation.