Wall shear stress in collapsed tubes

A small flexural wall rigidity brings unique features to cross-sectional sh apes and blood flow within veins, which are characterised by a non-uniform hemodynamical environment acting upon endothelial cells. Velocity fields an d related wall shear stress were numerically determined for a large number of conditions, assuming a fully developed, steady, incompressible laminar f low through an uniform smooth pipe with a constant cross-section. It was sh own that the flatness greatly influences the resulting distribution of the wall shear stresses along the lumen perimeter. For instance, under a steady longitudinal pressure gradient at about 500 Pascal per meter inside a cons tant oval-shaped tube, with a lumen perimeter of the order of 5 x 10(-2) me ter, the maximum wall shear stress is found at about 2 Pascal where the loc al curvature is minimal. On the other hand, the minimal wall shear stress o f the order of 1 Pascal is found where the local curvature is maximal. Clea r indications have been reported allowing that the hemodynamical wall shear stress does alter endothelial cell morphology and orientation. These resul ts are being used for developing an experimental set-up in order to locally map out the characteristic shear stresses looking for endothelial shape mo difications whenever a viscous fluid flow is applied.