Estimation of lymph flow by relating lymphatic pump function to passive flow curves.

Active pumping in postnodal lymphatic vessels is an important factor influencing lymph flow. However, the output of the lymphatic pump also depends on the rate of flow into the pump. This arrangement is similar to the blood circulation where cardiac output depends on the rate of blood flow through the veins into the heart (venous return) and on the pumping characteristics of the heart itself (cardiac function curves). One common way to analyze the blood circulation rate is to interrelate venous return and cardiac function curves. In this study, we used a similar technique to analyze lymph flow. We used lymphatic flow vs. outflow pressure (passive flow) relationships for nonpumping lymphatics to represent the inflow of lymph to the lymphatic pump. We used data on the pumping characteristics of postnodal lymphatic vessels to generate relationships between lymphatic pump outflow and pump inflow pressure (pump function curves), and then interrelated these curves. The results were not only similar to previously measured lymph flow data obtained from experimental animals, but also support the observation that under normal circumstances lymph flow is periodic and in surges (active pumping) but in edematogenic states lymph flows more continuously (i.e., passively).