Mechanical characteristics of lyophilized human saphenous vein valves.

PURPOSE: We investigated the mechanical characteristics of lyophilized human saphenous vein valves to determine their suitability for use as allogeneic transplants to treat chronic venous insufficiency. METHODS: Fresh cadaveric veins were lyophilized in vacuum bottles within 24 hours of harvest and were stored at room temperature. The veins were reconstituted in saline solution and then were placed in an in vitro flow circuit for evaluation. At varied flow rates, pressures proximal and distal to valves during prograde and retrograde flow were measured. Valve closure times were determined with Doppler examination and spectral analysis. The valves were also stressed to 350 mm Hg on a separate apparatus. RESULTS: All pressures proximal and distal to the valves remained less than 10 mm Hg during prograde flow. A pressure gradient developed immediately on the reversal of flow. Pressure as high as 200 mm Hg applied against the closed valves was not transmitted beyond the valve. Valve closure times had a mean of 0.31 +/- 0.03 seconds and 0.21 +/- 0.01 seconds for the Doppler examination and spectral analysis, respectively. All valves withstood stress pressures to 350 mm Hg. CONCLUSIONS: The in vitro mechanical characteristics of the valves of lyophilized veins are similar to known values for normal in vivo valves.

Accuracy of the inverse Womersley method for the calculation of hemodynamic variables.

We have studied the accuracy of the inverse Womersley method, a linear theory for the calculation of hemodynamic variables from measured volumetric flow rate or centerline velocity, for two canine arteries with different degrees of arterial wall motion and taper. The results from the linear theory are compared with the estimates from the nonlinear theory of Ling and Atabek for a canine thoracic aorta and femoral artery. For the thoracic aorta, the linear theory underestimates the mean wall shear stress by as much as 77%, when compared with the nonlinear theory. For the femoral artery, on the other hand, the mean wall shear stress value is underestimated by as much as 23%. Estimates of other hemodynamic variables show similar discrepancies between the nonlinear and linear theories. Thus, the inverse Womersley method does not give accurate estimates of hemodynamic quantities. This failure results from the neglect of convective accelerations due to arterial wall motion and taper, with the neglect of arterial taper leading to the largest errors.

Evaluation of the effect of retroviral gene transduction on vascular endothelial cell adhesion.

Genetically modified endothelial cells (ECs) seeded on synthetic vascular grafts offer the potential to improve small diameter vascular graft patency. Despite encouraging results with naive ECs, cells transduced with retroviral vectors appear impaired in their ability to adhere to and stably colonize vascular grafts in vivo. This study addresses changes in retrovirally transduced EC adhesion as the cause of cell loss. Endothelial cells were retrovirally transduced with the bacterial neoR gene or "mock" transduced with empty viral particles. Cells were allowed to adhere to collagen IV (CIV) or fibronectin (FN) prior to exposure to 20 or 90 dyn/cm(2) using a parallel plate apparatus. Cell detachment was evaluated using time lapse videomicroscopy. Fibronectin was a significantly better adhesive protein for naive EC than CIV at both shear stresses. NeoR-transduced EC had significantly greater detachment from FN than either naive or "mock"-transduced EC. Transduced EC attachment to FN was no greater than to CIV. Flow cytometric analysis of the fibronectin receptor (FNR) showed that transduced cells have reduced receptor expression compared to naive and "mock"-transduced EC. These results indicate retrovirally transduced EC have altered FNR and adhesion to FN and that these changes may account for transduced EC loss in vivo.

The effects of shear stress and metastatic phenotype on the detachment of transformed cells.

A parallel-plate flow chamber was used to quantify the detachment of normal, transformed, and reverted rat fibroblasts from a confluent monolayer of normal fibroblasts. In this method, known shear stresses were applied to the adherent cells and the percent of cells detached from the monolayer was determined. Results indicate that the detachment of all cell types increased with increasing shear stress and detachment of highly metastatic ras-transformed cells was significantly higher than that of either nonmetastatic normal cells or transformed cells reverted with the Kirsten ras revertant (K-rev 1a) gene, which are lowly metastatic. From these results, it is concluded that a correlation exists between the metastatic phenotype of the cell and its ability to detach from normal cells.