An in vitro comparison of the hemodynamics of two inferior vena cava filters

Purpose: The effectiveness of an inferior vena cava (IVC) filter in prevent ing pulmonary embolism while preserving caval flow is significantly affecte d by its hemodynamic characteristics. Flow fields surrounding two types of IVC filters were compared to assess how the design of a filter may influenc e performance. Methods: The 12F Titanium Greenfield and VenaTech LGM inferior vena cava fi lters were studied in vitro with a noninvasive flow visualization technique , the photochromic flow visualization and measurement technique. Axial velo city profiles and wall shear stress distributions were measured. These resu lts were compared with analytical data corresponding to the flow field in t he absence of a filter to determine the relative extent of the flow disturb ances. Results: The reductions in near-wall axial velocity and wall shear stress c aused by the VenaTech filter were more extensive and severe than those caus ed by the Greenfield filter. These changes were the consequence of differen ces in the geometry and dimensions of the struts of the two filters. The me asurements showed the flow fields to be laminar, with no evidence of turbul ence in both cases. Conclusion: Two factors that have been linked to thrombogenesis, near-wall velocity and wall-shear stress, were significantly affected by the larger f rontal profile area of the VenaTech filter. Although a larger area may incr ease clot-trapping efficiency, as shown by previous studies, the reduced ne ar-wall velocities and wall shear stresses may increase the potential for t hrombogenesis and, thus, caval occlusion. In contrast to other in vitro flo w visualization studies, no turbulence was observed with either filter.