Dai G, Gertler JP, Kamm RD.
The effects of external compression on venous blood flow and tissue deformation
in the lower leg.
J Biomech Eng 1999 Dec;121(6):557-64

Center for Biomedical Engineering, Massachusetts Institute of Technology, Cambridge 02139, USA.

External pneumatic compression of the lower legs is effective as prophylaxis
against deep vein thrombosis. In a typical application, inflatable cuffs are
wrapped around the patient's legs and periodically inflated to prevent stasis,
accelerate venous blood flow, and enhance fibrinolysis. The purpose of this study
was to examine the stress distribution within the tissues, and the corresponding
venous blood flow and intravascular shear stress with different external
compression modalities. A two-dimensional finite element analysis (FEA) was used
to determine venous collapse as a function of internal (venous) pressure and the
magnitude and spatial distribution of external (surface) pressure. Using the
one-dimensional equations governing flow in a collapsible tube and the relations
for venous collapse from the FEA, blood flow resulting from external compression
was simulated. Tests were conducted to compare circumferentially symmetric (C)
and asymmetric (A) compression and to examine distributions of pressure along the
limb. Results show that A compression produces greater vessel collapse and
generates larger blood flow velocities and shear stresses than C compression. The
differences between axially uniform and graded-sequential compression are less
marked than previously found, with uniform compression providing slightly greater
peak flow velocities and shear stresses. The major advantage of graded-sequential
compression is found at midcalf. Strains at the lumenal border are approximately
20 percent at an external pressure of 50 mmHg (6650 Pa) with all compression
modalities.