Endogenous plasminogen activator and venous flow: therapeutic implications.

This study is concerned with the changes in endogenous plasminogen activator (PA), in response to the augmentation of venous blood flow by external pneumatic compression (EPC). EPC was applied to the left leg in ten patients undergoing surgery under general anesthesia. Two-ml samples of venous blood were obtained from the left and right femoral veins and an arm vein at baseline (induction), and then at 30 and 60 min of compression. Ninety samples were analyzed in duplicate in a single blind technique, using an assay specific for PA activity. In the control right arm and leg, PA activity levels increased at 30 min (106% and 110% of baseline, respectively), and then declined to baseline levels by 60 min. These changes did not reach statistical significance. In the leg undergoing compression, however, PA activity decreased progressively, reaching 75% of baseline at 60 min (significant at both 30 [p less than .001] and 60 min [p less than .01] as compared to baseline). In vitro, PA activity varies directly with the concentration of fibrin. The progressive decline in activity in this study may, therefore, represent a decline in substrate (molecular fibrin), as a result of increased venous blood flow. Alterations in the activity of the endothelial cell, as observed, may lead to new approaches in the prophylaxis against thromboembolism.