A discrete model of the lymphatic system

This investigation establishes a theoretical base for studying the mechanisms of lymph propulsion from the periphery through the thoracic duct into the venous system. A discrete model of a lymph vessel is developed using the current concept that a lymph vessel consists of a number of compartments called lymphangions which are separated by valves. With the aid of the fundamental conservation laws, the equations governing the lymph flow in a lymph vessel are next identified. The model specifically considered the active contractibility of the walls of the lymphangions. The lymph vessel model is then used to develop a discrete model of the whole body human lymphatic system. The model is then coupled to a model of the interstitial fluid dynamics. The pressures in the arterial and venous ends of the capillaries, the external pressures on the walls of the lymphangions and the jugular venous pressure form the boundary conditions of the present model. The equations of the model are translated into a set of Fortran statements for the digital computer simulation of the model. The simulation results are in agreement with the available experimental results. The theory of lymphangion co-ordination is confirmed and extended. It is shown that the distention of the lymphangion wall plays a key role in activation and co-ordination of the lymphangion chains. This analysis further confirms the importance of the intrinsic contractibility in propelling lymph fluid form the periphery through the thoracic duct into the venous system. The flows in the lymphatic vessels are found to be intermittent. The frequency of the intrinsic contractions is found to depend on the inflow and accumulation of fluid in the lymphangions. Furthermore, it is found that if the outflow from a compartment is obstructed, the lymphangion pressure rises considerably due to the fluid accumulation in the lymphangions. Finally, the present analysis indicates that the lymph flow in the lymphatic system is achieved through a multi-stage pumping by the lymphangions