Pumping dynamics of a single lymphangion

We develop a three-dimensional fluid–structure interaction (FSI) computational model to investigate lymphatic pumping in a single lymphangion, a contractile segment of a lymphatic vessel bounded by elastic unidirectional valves. We model fluid pumping in a lymphangion undergoing periodic contractions with a prescribed amplitude. To establish a reference for pumping performance, we compare the simulation results with those of an idealized lymphangion model in which valves open and close instantaneously to enable unidirectional flow. Using our computational model, we quantify the effects of valve deformation and delayed closure on fluid transport and pumping efficiency. We show that elastic valves open and close gradually in response to flow, introducing a delay that leads to transient backflow. The delay is the most significant at higher Womersley numbers relating unsteady forces and viscous forces in oscillating flows. We find that the period-averaged flow rate remains largely independent of applied pressure gradients, confirming that prescribed wall contractions dominate net fluid transport. We also find that longer lymphangions provide more efficient fluid transport due to a reduced contribution of valve-related losses. We show that valve strain increases with lymphangion length, suggesting a physiological limit on lymphangion length to prevent valve degradation under excessive mechanical load.