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.
The micropipet aspiration technique and the parallel-plate flow chamber were used to investigate the deformation and detachment properties, respectively, of normal and transformed rat fibroblasts. The normal Cloned Rat Embryo Fibroblasts (CREF) cell line was transfected with the T24 ras oncogene to produce the transformed cell line CREF T24. The CREF T24 cell line was transfected with a Kirsten ras revertant gene (K-rev 1a suppressor) to produce the CT24HKB1 cells, which have the same morphological characteristics as the cells in the CREF line. The cells utilized in this investigation were derived from the parent cell line CREF, the only differences being the presence or absence of the T24 ras oncogene and the Kirsten ras revertant gene. The detachment and deformation properties, therefore, could be related to the metastatic phenotype of the cell rather than inherent differences between disparate cell lines. Results indicated that transfecting the CREF cell line with the ras oncogene greatly modified the detachment and deformation properties. The CREF T24 cells were more easily detached from normal cells and were 50% more deformable. Both CREF and CT24HKB1 showed similar detachment properties. Based on these results, it is speculated that K-rev 1a reversed ras-induced membrane alterations in these cells. Preliminary investigations have demonstrated that both CREF and CREF T24 cells in different phases of the cell cycle differed in morphological characteristics. However, the majority of the cells within a given cell line showed similar deformation characteristics. Current investigations are focusing on characterization of both detachment and deformation properties of these cells as a function of the cell cycle using synchronization techniques.
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