Applying the time-varying elastance concept to determine the optimum coordination of lymphangion contraction in a lymphatic vessel

The lymphatic system acts to return fluid from the interstitial space back into the blood circulation. In normal conditions, lymphangions, the segment of lymphatic vessel in between valves, cyclically contract and can pump lymph from low-pressure tissues to the higher-pressure veins of the neck. With edema, however, this pressure gradient can reverse, and the role of contraction is less clear. Like ventricles, lymphangions are sensitive to both preload and afterload. Unlike ventricles, lymphangions are arranged in series, so that the outlet pressure of one lymphangion becomes the inlet pressure of another. Anything that alters the relative timing of adjacent lymphangions alters both preload and afterload of each lymphangion and thus mean lymph flow. To explore the effect of timing of contraction on lymph flow, we developed a computational model of a lymphatic vessel with lymphangions described by classic description of time-varying elastance. When pumping up a pressure gradient, as in normal conditions, or when pumping down a pressure gradient, as in edema, we found that flow was optimized when the lymphangions in the vessel were pumping with a very little time delay between their cycles. However the flow was reduced when the time delay between the contractions was reduced to zero. This preliminary work provides evidence for a critical role for coordination of lymphatic contraction.