The role of stasis in the clotting of blood and milk flows around solid objects

A milk preparation has been used previously as an analogue for the study of flow related thrombosis in vitro. This paper describes further experiments to determine the comparability of milk clotting and thrombosis and to investigate the hydrodynamic correlates of milk clot deposition. An objective was to establish a standard in vitro test for thrombogenicity, thus facilitating the search for athrombogenic designs for prosthetic valves and other devices. Milk clotting in steady and pulsatile flow around four simple bodies of revolution showed many similarities of location and extent with in vivo canine thrombosis formation around similar bodies. A dye injection investigation of the fluid residence time distribution under the hydrodynamic conditions of the milk flow experiments showed that a permanent or trapped vortex persisted at each downstream site where clot was found, implying that stasis, or stagnation, is of predominant importance in causing milk clotting. Supplementary experiments with milk, using a modified Lee-White test, likewise showed that mixing promoted coagulation only after a certain fixed induction period from activation of the clotting process. Thus clot deposition is promoted by mixing which follows a constant induction period, rather than by mixing during an induction phase. This is a significant modification of the previous hypothesis.