Peristaltic pumping in short annular geometries: An experimental approach for studying Glymphatic flow

Abstract: Peristaltic pumping is hypothesized to drive fluid transport in several physiological systems, including cerebrospinal fluid flow through cerebral perivascular spaces (PVSs). Cerebral PVSs are unique in the context of peristaltic pumping because they have annular geometry and are orders of magnitude shorter than the peristaltic wavelength. Due to these features, questions were raised as to whether peristaltic pumping is possible under such conditions, and experimental tests for this concept are lacking. This work presents a novel experimental setup that enables direct, detailed measurements of peristaltic flow in short annular channels formed between a compliant inner tube and a rigid outer tube. A propagating pulse wave along the inner tube generates back and forth fluid motion in the annular gap, which we measure using particle tracking velocimetry in a refractive-index matched setup. Despite the instantaneous back and forth motion, net axial fluid transport in the direction of wave propagation is observed, and the resulting net velocity profiles collapse across a range of wall deformation amplitudes. These results provide experimental evidence for net transport induced by long wave length peristaltic deformations in a physiologically relevant flow regime.