On the appropriateness of modelling brain parenchyma as a biphasic continuum

We carried out a series of simple experiments using lamb and sheep brain tissue to establish the rate at which cerebrospinal fluid moves through the brain parenchyma. Mindful of possible variations in hydraulic conductivity with tissue deformation, our intention was to carry out our experiments on brain tissue subjected to minimal deformation. This has enabled us to compare the rate of flow with values predicted by some of the theoretical values of hydraulic conductivity from the literature. Our results indicate that the hydraulic conductivity of the brain parenchyma is consistent with the lowest theoretical published values. These extremely low hydraulic conductivities lead to such low rates of CSF flow through the brain tissue that in effect the material behaves as a single-phase deformable solid.