The effect of sustained venous hypertension on the skin capillaries of the canine hind limb.

An increased number of skin capillaries has been found in human skin subjected to sustained venous hypertension. To investigate this observation, venous hypertension was produced in the hind limb of Greyhounds by fashioning an arteriovenous (AV) fistula between the femoral vessels. This caused an increase in the number of capillaries in the skin of the lower leg. The capillary permeability of normal legs and legs subjected to chronic venous hypertension was then studied by observing the movement of radioactive molecules from the plasma to the fluid within Guyton capsules. Fibrinogen, a large molecule, leaked out of the capillaries significantly faster in the limbs with a high venous pressure and an enlarged capillary bed. It is suggested that the increase in the size and permeability of the dermal skin capillaries secondary to prolonged venous hypertension is the cause of lipodermatosclerosis and venous ulceration.