Haemostatic Clot Formation at Anastomosis of Synthetic Venous Graft in Defibrinogenated Dogs: A Scanning Electron Microscopic Study

Erythrocyte aggregation and erythrocyte deformability modify the permeability of erythrocyte enriched fibrin network

Intravascular thrombus formed under low shear conditions consists of red cells enmeshed within a fibrin network. Since red cells reduce the permeability of fibrin network by surface drag and by volume occupancy the significance of red cell aggregability and deformability in network permeability needs examination. In this study networks were developed by the addition of thrombin to washed red cells suspended in platelet free plasma. The effects of the polymers polyvinylpyrrolidone (PVP) and poloxamer 188 on network permeability were compared to gauge the influence of red cell aggregation. Both polymers increase network permeability by an action on fibrin polymerisation but PVP alone enhances red cell aggregation. PVP was found to increase network permeability significantly both by increasing the permeability of the fibrin component of the network and by increasing red cell aggregation and thus reducing red cell surface drag. In separate experiments red cells were pre-treated with heat, glutaraldehyde, or diamide to reduce cell deformability. Decreased cell deformability caused significant reductions in network permeability. This was ascribed to the reduced aggregability of hardened red cells. Red cell aggregation during coagulation enhances molecular transport through modifying the network. This may have implications for the penetration of fibrinolytic agents.

Pseudoendothelium formation in expanded polytetrafluoroethylene grafts implanted in the inferior vena cava of normal and defibrinogenated dogs

The outgrowth of endothelial cells in an expanded polytetrafluoroethylene graft implanted in the canine inferior vena cava was studied by scanning electron microscopy. The adjacent endothelial cells of the vena cava started to invade the anastomotic area three days after the implantation and reached approximately the central part of the 2-cm-long graft after 21 days. There was no obvious difference in the process of endothelialization between the control group and the moderately defibrinogenated group, in which the fibrinogen concentration was at most 0.72-0.87 gm/L. A slight delay in the outgrowth of endothelial cells was noted within the first seven days in the severely defibrinogenated group, in which the fibrinogen concentration was below 0.40 gm/L. After 70 days, all grafts were completely covered by endothelial cells. The structural difference of the mural thrombus resulting from reduced fibrin formation might be a major factor influencing the endothelium formation.