ИСТИНА

Background: Rheological conditions profoundly affect adhesion, activation and aggregation of platelets in vivo, and also affect local concentrations of coagulation factors inside and out of thrombus. Any pathological condition, be it stenosis or traumatic puncture of vessel wall, creates novel rheological conditions at the injury site. However, there is little information on these rheological conditions, in particular, for the acute conditions of partial vessel occlusion and puncture. Aims: Our aim was to investigate rheological conditions that arise at the injury site and in the intact part of circulatory system. Methods: A computer simulation of blood circulation in the human arm was carried out to model rheological changes at the micro- and macro-scales. The model assumed that intact vessels have rigid walls and blood is Newtonian fluid. Flow in intact vessels was considered in one dimensional space (1D) and in 3D when propagating through the injury region. Based on Hagen-Poiseuille’s law, Navier-Stokes and continuity equations and experimental knowledge of sizes of vessels, a system of corresponding algebraic and differential equations was solved for flux, pressure and velocity fields. Results: When median cubital vein was punctured, the pressures at the ends of injured vessel decreased with increase of the radius of the wound (up to 42% compared with intact system). Pressures in other nodes decreased by less than 1%. The blood flow from the supply vessels increased (up to 74%), and the outflow from the discharge vessels decreased. In basilic vein it stopped completely (at radius of wound about 700 um) and changed its direction (to 18% of the value in intact vessel). The flow changes did not extend (a change less than 0,6%) to the deep veins. Flow lines near the wall opposing injury did contain a curved section suggesting that blood cells circulate in the injury area before passing through the wound near the damaged wall. For realistic macroscopic injuries (more than 300 um), the rate of the blood loss was determined by resistances of the supply vessels and the shear rate decreased with increasing wound size. For small injuries, it mostly depended on the resistance of the wound. Shear rate increased (up to 10^5 c^-1 ) with the wound size (less than 300 um) in this mode. Summary/Conclusion: These data provide insight into how traumatic puncture affects flow redistribution in a circulatory system, and how hydrodynamic resistances of the vessels and of the wound determine blood loss and conditions for the hemostatic system functioning.