Pump efficacy in a fluid-structure interaction model of a chain of contracting lymphangions

TL;DR

This study presents a computational fluid-structure interaction model of lymphangion chains, revealing how chain length, contraction style, and pressure differences influence lymph flow efficiency and valve dynamics.

Contribution

The paper introduces a 2D Navier-Stokes based model with immersed boundary method to analyze lymph flow in contracting lymphangions, highlighting effects of chain length and contraction timing.

Findings

Longer lymphangion chains produce higher flow rates.

Simultaneous contractions generate larger flow rates than non-simultaneous.

Higher adverse pressure differences reduce flow in longer chains.

Abstract

The transport of lymph through the lymphatic vasculature is the mechanism for returning excess interstitial fluid to the circulatory system, and it is essential for fluid homeostasis. Collecting lymphatic vessels comprise a significant portion of the lymphatic vasculature and are divided by valves into contractile segments known as lymphangions. Despite its importance, lymphatic transport in collecting vessels is not well understood. We present a computational model to study lymph flow through chains of valved, contracting lymphangions. We used the Navier-Stokes equations to model the fluid flow and the immersed boundary method to handle the two-way, fluid-structure interaction in 2D, non-axisymmetric simulations. We used our model to evaluate the effects of chain length, contraction style, and adverse axial pressure difference (AAPD) on cycle-mean flow rates (CMFRs). In the model, longer lymphangion chains generally yield larger CMFRs, and they fail to generate positive CMFRs at higher AAPDs than shorter chains. Simultaneously contracting pumps generate the largest CMFRs at nearly every AAPD and for every chain length. Due to the contraction timing and valve dynamics, non-simultaneous pumps generate lower CMFRs than the simultaneous pumps; the discrepancy diminishes as the AAPD increases. Valve dynamics vary with the contraction style and exhibit hysteretic opening and closing behaviors. Our model provides insight into how contraction propagation affects flow rates and transport through a lymphangion chain.