Bioengineering studies of periodic external compression as prophylaxis against deep vein thrombosis-part II: experimental studies on a stimulated leg.

In this companion paper to "Part I: Numerical Simulations, " we report in vitro experimental studies performed on a simple model leg consisting of a "vein" of thin-walled latex tubing surrounded by "tissue" of open-pore foam rubber. Three modes of periodic external compression, were investigated: i) uniform compression; (ii) graded compression, decreasing from ankle to knee; and (iii) sequential compression, progressing from ankle to knee. The modes are compared on the basis of three hemodynamic criteria: degree of vessel collapse, level of fluid velocity, and level of shear stress. In uniform compression these measures of merit are distributed very nonuniformly along the length of the leg: they are high near the proximal end of the cuff but low elsewhere, a result due to the formation proximally of a partially occlusive throat. The latter does not form in either graded or sequential compression, with the consequence that favorable values of the three measures of merit occur more uniformly along the length of the pressurized region. It is concluded that either the graded or sequential mode of compression, or perhaps a combination of the two, would be more effective than uniform compression as a prophylaxis against deep vein thrombosis.