The lymphatic system is an important vascular network that plays a vital role in physiologic function. The lymphatics are generally tubular vessels segmented by bi-leaflet valves. These vessels are small (~100 µm diameter) with low flow-rates, making them a challenge to investigate experimentally. Their resistance to flow, an important parameter in determining pumping function, is thus extremely difficult to estimate. We are thus constructing computational fluid and solid mechanics models of lymphatic valves to facilitate a more complete characterisation.
Idealised Geometry: Confocal images of isolated rat mesenteric lymphatic vessels were used to aid in the construction of an, “idealised,” lymphatic vessel geometry that consists of a sinus region encapsulating a set of lymphatic valves.
Solid Mechanics Modeling: A Finite Element Analysis (FEA) was performed to simulate the opening behaviour of the valve from an initially closed configuration using a uniform pressure of 4 dyne/cm^2. The coordinates of the leaflet surfaces of the deforming valve were extracted every 0.01 s until they were in the fully open state.
CFD Modeling: The initial valve coordinates were used to create a polyhedral volume mesh in STAR-CCM+. The morphing option in the solver was activated and the nodal coordinates obtained throughout the FEA simulation were used as boundary conditions for the geometry. Constant pressure boundary conditions were applied at the inlet and outlet. Mesh refinement showed less than 1% root-mean-square difference in wall shear stress using 655,846 elements.The axial pressure drop across the leaflets was calculated to generate resistance data over time. After the orifice area reaches one-third of its maximum value (time~0.05s), the valve resistance to flow is between 3.41 X 10^6 and 4.22 X 10^6 g/cm^4/s. This work forms the basis of further studies building towards a more strongly coupled fluid/solid model.