Optimal Lymphatic Vessel Structure

Abstract

Lymphatic vessels transport excess interstitial fluid from the low-pressure tissues to the higher pressure veins. The basic structural unit of lymphatic vessels is the lymphangion, a segment of the vessel separated by two unidirectional valves. Lymphangions cyclically contract like ventricles and can actively pump lymph. Lymphangions, as conduit vessels, also can act as arteries, and resist lymph flow. Functional parameters such as pressures, flow, and efficiency are determined by structural parameters like length, radius, and wall thickness. Since these structural parameters are unalterable experimentally, we developed a computational model to study the effect of a particular structural parameter, lymphangion length, to a particular functional variable, lymph flow. The model predicts that flow is a bimodal function of length, exhibiting an optimal length in the same order of magnitude as that observed experimentally. In essence, when the length to radius ratio is small, lymphangions act more like ventricles, where longer lengths yield greater chamber volume and thus lymph pumped. When the length to radius ratio is large, lymphangions act more like arteries, where longer lengths yield greater resistances to flow. This approach provides the means to explore how lymphatic vessel structure is optimized in a variety of conditions.

Optimal postnodal lymphatic network structure that maximizes active propulsion of lymph

“…This study revealed that the average flow through a lymphatic vessel remained unaffected by the propagation direction of its contractile waves. Although these models were evaluated numerically, they allowed manipulation of parameters, such as length and contractility, that cannot be experimentally controlled (32). The complexity of numerical solutions, however, increases dramatically when an attempt is made to model more than a few lymphangions because of the large number of required parameters.…”

A multiscale sliding filament model of lymphatic muscle pumping

“…While there have been multiple computer models phenomenologically incorporating both phasic and tonic contractions of lymphatic muscle (Caulk et al 2016;Caulk et al 2015;Kunert et al 2015;Razavi et al 2020;Razavi et al 2017), the different effects of the contraction types were the focus of only one series of computational modelling papers. This model used the time-varying elastance model of the heart combined with the transmission line equations for blood vessels (Quick et al 2008;Venugopal et al 2007;Venugopal et al 2010;Venugopal et al 2004;Venugopal et al 2003).…”