Changes in Clotting and Fibrinolytic Parameters Produced by Venous Stasis

Abstract

Vascular endothelial cells have thrombosis- prevention properties through the release of some fibri nolytic factors. This capacity of endothelium was studied using the venous occlusion test (VOT) and measuring proteins released during stasis. Blood samples were col lected before and after 10 and 20 min VOT in tubes con taining sodium citrate at pH 7.0 or 4.3. A significant shortening of the euglobulin clot lysis time (ECLT) was obtained 10 and 20 min after VOT in plasma collected in citrate pH 7.0 or 4.3. No statistical difference was noted between results obtained 10 and 20 minutes after VOT. The shortening was related to the increase of tissue plas minogen activator (t-PA) released during VOT. No differ ence was detected in the concentration of tissue plasmin ogen activator inhibitor 1 (PAI-1), but PAI-1 activity mea sured in plasma from blood collected in citrate pH 7.0 decreased progressively from 10.8 ± 9.2 arbitrary units (AU)/ml to 3.76 ± 4.5 AU/ml and 0.8 ± 1.02 AU/ml (p < 0.001) after 10 and 20 min, respectively, of stasis. When the PAI-1 activity was determined in blood collected in citrate pH 4.3 for preventing in vitro complexing of PAI-1 and t-PA, results were different: PAI-1 activity decreased from a basal value of 29.2 ± 15.3 AU/ml to 24.9 ± 12.2 ( p = NS) and 18.7 ± 11.5; p < 0.02) 10 and 20 min after VOT. As result of fibrinolytic activation, other factors were modified: increase of plasminogen activators, de crease of plasminogen, and increase of D-dimer. Fibrin ogen, fibronectin, protein C, protein S, von Willebrand factor, and tissue factor pathway inhibitor concentration remained unchanged after VOT. According to our find ings, VOT can be performed with a stasis of 10 min. Good responders are related to the endothelial capacity for re leasing t-PA and urokinase-type PA (u-PA) and defined as those with an ECLT of <60 min after 10 min VOT when blood was collected in sodium citrate pH 7.0.