The effects of external compression on venous blood flow and tissue deformation in the lower leg

External pneumatic compression of the lower legs is effective as prophylaxi s against deep vein thrombosis. In a typical application, inflatable cliffs are wrapped around the patient's legs and periodically inflated to pr-even t stasis, accelerate venous blood flow, and enhance fibrinolysis. The purpo se of this study was to examine the stress distribution within the tissues, and the corresponding venous blood flow and intravascular shear stress wit h different external compression modalities. A two-dimensional finite eleme nt analysis (FEA) was used to determine venous collapse as a function of in ternal (venous) pressure and the magnitude and spatial distribution of exte rnal (surface) pressure. Using the one-dimensional equations governing pow in a collapsible tube and the relations for venous collapse from the FEA, b lood pow resulting from external compression was simulated. Tests were cond ucted to compare circumferentially symmetric (C) and asymmetric (A) compres sion and to examine distributions of pressure along the limb. Results show that A compression produces greater vessel collapse and generates larger bl ood flow velocities and shear stresses than C compression. The differences between axially uniform and graded-sequential compression are less marked t han previously found, with uniform compression providing slightly greater p eak pow velocities and shear stresses. The major advantage of graded-sequen tial compression is found at midcalf Strains at the lumenal border are appr oximately 20 percent at art external pressure of 50 mmHg (6650 Pa) with all compression modalities.