IN-VITRO ASSESSMENT OF THE HEMODYNAMIC-EFFECTS OF A PARTIAL OCCLUSIONIN A VENA-CAVA FILTER

Purpose: Flow fields surrounding a vena cava filter were studied with a noninvasive method of flow visualization to examine the underlying h emodynamic factors that contribute to its function and patency. Method s: The photochromic technique was used to measure axial velocity profi les and wall shear stress distributions in a 12F titanium Greenfield f ilter partially occluded with a simulated volume of entrapped thrombi. These results were compared with similar measurements obtained for an unoccluded filter and with a theoretic prediction of the velocity pro file and wall shear stress without a vena cava filter. Shear stress di stributions were obtained along the vessel wall and for the partially occluded filter along the surface of the simulated clot. Results: The unoccluded filter was observed to have little effect on the flow field . In the case of the partially occluded filter, the results of these m easurements show that caval blood flow is preserved by the creation of an annular region of increased flow around the periphery of the clot. Within this region high shear stresses that develop as a result of th e increased flow are observed along the vessel wall and along the surf ace of the simulated clot. No vortices or turbulence were observed wit h either the unoccluded or the partially occluded filter. Conclusions: The elevated levels of shear stress may be a factor in the lysis of t rapped clots observed in vivo. Although increased shear stress is repo rted to cause thrombogenesis in an in vivo study in canines, particula rly under turbulent flow conditions, the levels of shear measured in t his study around the simulated clot were well below such values.