An animal model of venous hypertension: the role of inflammation in venous valve failure

BACKGROUND: Clinical observation suggests that chronic venous insufficiency is related to failure of venous valves. Duplex ultrasound studies of lower extremity superficial veins regularly show valve failure and venous reflux. Gross morphologic observation of venous valves in surgical specimens shows tearing, splitting, scarring, and disappearance of valves. HYPOTHESIS: Venous valve damage is acquired, linked with venous hypertension, and affected by inflammation. OBJECTIVE: The objective of this study was to investigate the inflammatory process in valve remodeling associated with acute and chronic venous hypertension. METHODS: A femoral arteriovenous fistula was created in study animals (Wistar rats, n = 60), and animals without an arteriovenous fistula were studied as controls (n = 5). At 1, 7, 21, and 42 days animals with the femoral arteriovenous fistula were anesthetized, and systemic pressure, the pressure in the femoral vein distal to fistula, and the pressure of the femoral vein in the contralateral hind limb were measured. Timed collection of blood backflow after division of the femoral vein distal to the fistula and in the alive, anesthetized animal was collected, measured, and calculated per unit time to be used as an indicator of valve insufficiency. The femoral vein distal to the fistula was harvested; valvular structures were examined and measured. Specimens were processed, and longitudinal sections were made and challenged with immunostaining antibodies against matrix metalloprotease (MMP)-2 and MMP-9. Sections were examined, and expression of molecular markers was determined by light absorption measurements after image digitization. RESULTS: One week after the procedure, all animals exhibited some degree of hind limb edema ipsilateral to the arteriovenous fistula. Pressure in the femoral vein distal to the fistula was markedly increased on average to 96 +/- 9 mm Hg. Reflux was increased in a time-dependent manner, with the 21-day and 42-day groups showing the highest values. Valves just distal to the fistula showed an increased diameter of the valvular annulus and a shortening of the annular height. Venous wall findings included fibrosis and fusion of the media and adventitia and scarring and disappearance of valves principally in the 21- and 42-day specimens. Immunolabeling for MMP-2 showed an increased level in the 21- and 42-day groups. MMP-9 showed an increased level at 1 day, followed by a more marked level in the 21- and 42-day groups. CONCLUSIONS: In this animal model of venous hypertension the findings of limb edema, increasing valvular reflux, and morphologic changes of increased annulus diameter and valve height are seen. Histologic changes included massive fibrosis of media and fusion with adventitia. Inflammatory markers MMP-2 and MMP-9 are strongly represented, and valve disappearance occurs after these markers are present. The gross morphologic changes seen are quite similar to those observed in human surgical specimens removed in treatment of venous insufficiency. CLINICAL RELEVANCE: When observed angioscopically at the time of vein stripping, saphenous vein valves show severe deformities including shortening, scarring, and tearing. The current model of induced venous hypertension demonstrates early venous valve changes that replicate those observed in humans. This observation provides a link from venous hypertension to an induced inflammatory reaction that stimulates the valve damage. Thus the model could be useful for defining the fundamental mechanisms that cause venous valve failure and varicose veins and in pharmacologic testing to prevent or treat venous insufficiency.