title: In vitro evaluation of a new temporary venous filter: the Spring filter.
abstract: OBJECTIVE
  To evaluate in vitro the function efficacy of a new variable-sized, temporary venous filter, the Spring filter (SF).
  
  
  METHODS
  The SF was tested in a flow phantom, using flexible, thin-walled polyethylene tubes 12, 14, and 16 mm in diameter to simulate veins. Clots of three sizes were used: 6 x 10 mm, 6 x 20 mm, 9 x 20 mm. Filter deployment was performed, ensuring that its functional diameter after placement was a predetermined multiple of the radius 'r' of the tube: 3.0r, 2.8r, 2.6r, 2.4r. The terminal coil was visually examined for changes in configuration. Clot retention by the filter for a period of 3 min was recorded as a success. The baseline intraluminal pressure and the maximum pressure reached after clot introduction were recorded. The trapping ability was calculated from the results for 10 clots. The effect of the following parameters on filter function were studied: size of embolus, caliber of simulated vein, and functional diameter of filter.
  
  
  RESULTS
  The filter configuration was stable. Not a single instance of axial tilting occurred on deployment. Functional diameter was the major determinant of filter function. One hundred percent of clots were trapped irrespective of clot size and tube caliber when the functional diameter was 3.0r. Only 73% (95% confidence interval (CI): 57% - 88%) and 77% (95% CI: 61% - 92%) of small emboli were held up by the filter when the functional diameters were 2.6r and 2.4r, respectively (p = 0.0001). A significant reduction in clot trapping was encountered even with medium clots when the functional diameter was 2.4r (p = 0.02).
  
  
  CONCLUSIONS
  Against the background of available data on retrievable vena caval filters, the current model of SF warrants further investigation.
authors.affiliation: Institute for Surgical Research, National Hospital (University of Oslo), Norway.
authors.forename: Z Y
authors.initials: ZY
authors.lastname: Xian
authors.forename: S
authors.initials: S
authors.lastname: Roy
authors.forename: J
authors.initials: J
authors.lastname: Hosaka
authors.forename: K
authors.initials: K
authors.lastname: Kuroki
authors.forename: K
authors.initials: K
authors.lastname: Kvernebo
authors.forename: I
authors.initials: I
authors.lastname: Enge
authors.forename: F
authors.initials: F
authors.lastname: Laerum
mesh_terms: D004867:Equipment Design; D006801:Humans; D019047:Phantoms, Imaging; D013927:Thrombosis / Q000628:therapy; D016306:Vena Cava Filters