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.
|Original language||English (US)|
|Journal||Journal of the Royal Society Interface|
|State||Published - Nov 1 2020|
Bibliographical noteFunding Information:
This work was supported by the NIH/National Institute of Aging (grant no. RF1AG057575) and by the US Army Research Office (grant no. MURI W911NF1910280). J.T. is partially supported by a Career Award at the Scientific Interface from Burroughs Wellcome Fund.
© 2020 The Author(s).
- brain clearance system
- cerebrospinal fluid
- fluid dynamics
- glymphatic system
- hydraulic network models
- perivascular spaces