Changes in the Vessel Wall
Functional changes in the endothelial lining of the vessel wall are now being examined in greater detail. Abnormal platelet, leukocyte, and endothelial activation by cells may be an important factor in the genesis of a thrombus, but endothelial damage alone only produces cellular adhesion, not thrombus in an animal model.
Eddy currents within valve pockets may cause localized endothelial disturbance or activation, which promotes leukocyte and platelet adhesion. In animal studies leukocyte-mediated disturbance of endothelium occurs before platelet and red cell deposition are observed, and this has been proposed as an initiating mechanism.
Thrombus formation is reduced by substances that inhibit leukocyte adhesion and migration in animal models and in patients having hip replacements.No significant increase in the expression of adhesion receptors has, however, been found during thrombin-induced experimental thrombogenesis in man.Prolonged stasis does upregulate endothelial adhesive receptors in the rabbit external jugular vein, causing increased adhesion of leukocytes to the vessel wall, although this does not progress to endothelial damage and thrombus
generation.
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