Figure 3.

Simulations of arterial pulsations in a model with an elliptic PVS show that observed fluid flows are inconsistent with a peristaltic pumping mechanism. (a) The 3D geometry of the PVS used in our simulations replicates the PVS geometry observed in vivo in mice. The figure in top-left is taken from Mestre et al.⁷ and the figure on the bottom-right shows the 3D geometry used in our calculations. (b) The dimensions and boundary conditions used in 3D fluid dynamics simulations. The wall movement on the arterial side (orange) is given by a travelling wave with a realistic waveform observed in vivo in mice⁷ (inset). The wall on the brain tissue side is fixed (green). The parameters (R₁, R₂, λetc are given in Table 1). (c) Plots showing the arterial wall velocity and the centerline velocity of the fluid taken at the same axial (z) location. While the wall velocity profile and magnitude are very similar to what was observed in vivo⁷, the oscillatory fluid velocity is ~1000x higher than the values observed in vivo^6,7. Moreover, the peak fluid velocity is not in phase with the wall velocity. These discrepancies were predicted by our simplified model (Fig. 2). (d) The colors show axial velocity profile at the mid-section of the PVS (XZ plane at y = 0) throughout the cardiac cycle. Arrows are provided to make the interpretation of flow easier. The fluid velocity profile agrees with our expectations from the mechanism of peristalsis (Fig. 2b) and our simplified model (Fig. 2c). The deformations are increased by a factor of 50 in post-processing to clearly show the arterial wall movement. (e) Corresponding pressure profile at the mid-section of the PVS (XZ plane at y = 0) throughout the cardiac cycle. The deformations are scaled by a factor of 50 in post-processing to clearly show the arterial wall movement. All the subplots were generated with COMSOL Multiphysics 5.4(http://comsol.com), with the exception of the top left image in a (citation provided).