Summary
A technique has been developed which allows an estimation of the clotting tendency
of blood under conditions which simulate in vivo flow in various regions of the circulatory
system. Minimum contact between blood and foreign surfaces other than the walls of
the tubular test cell is obtained. Early pre-clotting and clotting events which alter
the apparent viscosity of blood are resolved within three seconds of their onset.
Increases in apparent viscosity slow the oscillations of the test system, and frequency,
differential frequency, or amplitude can be monitored continuously. A standard tubing
material may be used to evaluate effects of antithrombotic or other agents. For the
present studies, the instrument was used with native blood at 28° or 37° C to produce
shear rates comparable to those present in venous flow. Gum rubber, vinyl, glass and
silicone tubing have been investigated for their effects on activation of the intrinsic
coagulation system of human blood. In order of increasing-time to formation of thrombus
are glass, vinyl, rubber, silicone. Thrombi were adherent to glass and rubber but
not to Tygon or Silastic tubes. Time sequence studies during flow in silicone tube
with native blood indicate progressive shortening of Stypven and partial thromboplastin
time values, and progressive decrease in leukocyte and platelet counts. Addition of
a commercial bovine collagen preparation to native normal blood in Silicone tubing
decreased the thrombus time value by 40% while addition of the experimental agents
RA 233 or VK 744 decreased this value by 50% and 70% respectively. Aspirin therapy
produced a 158% increase in thrombus time values. Light microscopic studies of thrombi
formed in this closed system revealed thrombus structure comparable to that of classic
venous thrombi.
