Computational simulation of diaphragmatic lymphatics' intrinsic activity

Spontaneous contractile activity has been observed in FITC-dextran-filled lymphatic vessels located along the peripheral margin of the pleural diaphragm in anesthetized adult Wistar rats. Based on their contractile behavior, individual lymphatic segments were grouped into four functional categories: active spontaneously contracting, stretch-responsive, passive, and non-contractile. Unlike central collectors, the most peripheral loops of the diaphragmatic lymphatic network, located in the muscle adjacent to the abdominal wall, depend on an intrinsic mechanism to drive lymph propulsion. Using ex vivo video microscopy, fluorescent particle motion was tracked along one such spontaneously contracting vessel, and a representative active segment was modeled in COMSOL Multiphysics. From the experimentally derived changes in vessel diameter, parameters such as transported volume and inlet-outlet flow rates were quantitatively estimated.