UVM Theses and Dissertations
Format:
Print
Author:
Trotman, Winifred E.
Title:
Dept./Program:
Pathology
Year:
2010
Degree:
MS
Abstract:
Deep venous thrombosis (DVT) refers to a blood clot arising in one of the major deep veins of the lower legs, thighs, or pelvis. In the United States, about 2 million people per year develop deep vein thrombosis. Most of them are aged 40 years or older. There are three broad categories of factors that are thought to contribute to the onset of thrombosis; reduction in the flow and/or pulsatility of blood flow, alteration ofthe procoagulant/anticoagulant balance in the blood, and a loss of vascular wall integrity. Deep venous valves are generally accepted as frequent sites of deep venous thrombosis initiation. Thrombus initiation at these sites is commonly attributed to stasis which has been objectively observed in venography studies where contrast media lingers in the valvular sinuses for up to half an hour following the study (McLachlin et al., 1960). Stasis promotes coagulation by bringing platelets into contact with the endothelium, and preventing both the dilution of activated clotting factors as well as the influx of clotting factor inhibitors by fresh flowing blood. Stasis alone, however, does not seem to be a sufficient explanation for venous thrombosis. The onset of clinical disease is usually accompanied by acquired and/or genetic risk factors for thrombosis.
Valvular sinus stasis has been associated with hypoxia and increased hematocrit (Hamer et al., 1981). The increase in hematocrit likely includes increased opportunity for leukocytes to interact with the vessel wall, the initiation site of venous thrombosis (Wakefield et al., 2008). Prolonged hypoxia likely promotes endothelial cell activation (Hamer et al., 1981). These phenomena together create a potentially hypercoagulable micro-environment at the venous valvular sinus wall which is thought to be the anatomic site of thrombus initiation.
Investigation of the deep venous system is difficult because direct intervention in these veins is associated with significant morbidity and risk for thrombosis. However, saphenous veins (SV) remaining after coronary artery graft bypass (CABG) procedures are a readily available model. Thus, valves from post CABG SVs were trisected and processed for analysis of procoagulant and antic9agulant proteins in the venous valves by quantitative immunofluorescence confocal microscopy. We hypothesized that increased stasis in the deeper recesses of the venous valves would be associated with a gradient of increased thromboresistance from the proximal to the distal sinus. We also hypothesized that the valve sinus endothelium anticoagulant/procoagulant balance would be altered to favor thromboresistance in comparison with the nonvalvular lumenal endothelium.
In support of our hypothesis, we found endothelial expression ofthe procoagulant protein von Willebrand Factor (vWF) in the valve sinus decreased from the uppermost to the deepest region ofthe valve sinus (p=0.002). In addition, significantly decreased expression of vWF was observed in the valve sinus compared to the non-valvular sinus endothelium. In contrast, endothelial expression patterns ofthe anticoagulant proteins thrombomodulin (TM) and endothelial protein C receptor (EPCR) did not support our hypothesis. Endothelial expression of TM and EPCR were not significantly increased in the venous valve sinus. In contrast to our hypothesis, EPCR expression decreased from the uppermost to the deepest region of the valve smus and TM expression remained unchanged throughout the valve sinus.
Valvular sinus stasis has been associated with hypoxia and increased hematocrit (Hamer et al., 1981). The increase in hematocrit likely includes increased opportunity for leukocytes to interact with the vessel wall, the initiation site of venous thrombosis (Wakefield et al., 2008). Prolonged hypoxia likely promotes endothelial cell activation (Hamer et al., 1981). These phenomena together create a potentially hypercoagulable micro-environment at the venous valvular sinus wall which is thought to be the anatomic site of thrombus initiation.
Investigation of the deep venous system is difficult because direct intervention in these veins is associated with significant morbidity and risk for thrombosis. However, saphenous veins (SV) remaining after coronary artery graft bypass (CABG) procedures are a readily available model. Thus, valves from post CABG SVs were trisected and processed for analysis of procoagulant and antic9agulant proteins in the venous valves by quantitative immunofluorescence confocal microscopy. We hypothesized that increased stasis in the deeper recesses of the venous valves would be associated with a gradient of increased thromboresistance from the proximal to the distal sinus. We also hypothesized that the valve sinus endothelium anticoagulant/procoagulant balance would be altered to favor thromboresistance in comparison with the nonvalvular lumenal endothelium.
In support of our hypothesis, we found endothelial expression ofthe procoagulant protein von Willebrand Factor (vWF) in the valve sinus decreased from the uppermost to the deepest region ofthe valve sinus (p=0.002). In addition, significantly decreased expression of vWF was observed in the valve sinus compared to the non-valvular sinus endothelium. In contrast, endothelial expression patterns ofthe anticoagulant proteins thrombomodulin (TM) and endothelial protein C receptor (EPCR) did not support our hypothesis. Endothelial expression of TM and EPCR were not significantly increased in the venous valve sinus. In contrast to our hypothesis, EPCR expression decreased from the uppermost to the deepest region of the valve smus and TM expression remained unchanged throughout the valve sinus.