Figure 3.

(A) Comparison of theoretical estimates and experimental data relating the combined tortuosity λ to the effective radius of diffusing molecules. Circles, experimental estimates of the extracellular tortuosity in the rat cortex for four different dextrans (Stokes radii R are shown on the abscissa) by Tao and Nicholson (29, 30). Dashed line, theoretical prediction based on Eq. 9 with no adjustable parameters. (B) Comparison of theoretical estimates and experimental data relating the combined tortuosity λ to the extracellular volume fraction α. Filled circles, experimental estimates of α and λ measured with TMA⁺ diffusion in the turtle cerebellum by Krizaj et al. (21), perfused with solutions of different osmolarities. Open circles, estimates of α and λ obtained in the rat neocortex by Pérez-Pinzón et al. (13) and Voříšek and Syková (15) in conditions of induced ischemia (combined data). Curves, corresponding theoretical estimates of λ(α), in accordance with Eq. 10 with one adjustable parameter, φ, the volume fraction occupied by large extracellular macromolecules.