Overview of Lower Extremity Circulation

The circulation of the lower extremity comprises three types of vessels: Arteries, Veins, and Lymphatics. This overview will focus primarily on the veins or venous system.

Arteries are the vessels that take oxygenated blood from the heart to all areas of the body including the thighs, legs, and feet. Unless one is a smoker or diabetic, these vessels typically function well throughout life. Arteries are extremely important as we have a limited number of them.

Veins or the venous system return deoxygenated blood from all areas of the body to the heart and lungs for re-oxygenation.

In the lower extremities, the venous system is divided into two categories: the Deep Veins and the Superficial Veins. The superficial veins run under the skin in the subcutaneous layer and collect a relatively small volume of blood. The superficial veins drain this blood into the deep veins which in turn return the blood to the heart. The superficial veins carry much less than 1% of the lower extremity circulation.

Varicose veins are enlarged superficial veins. Superficial veins usually are so small we do not see them in the lower extremity. Unlike the lower extremities, normal superficial veins are commonly seen in the arms and hands, usually due to less subcutaneous fat. If superficial veins become stretched or dilated in the lower extremities, they become visible.

Visible varicosities have become nonfunctional as the valves in these veins have developed leaks.

The pressure on the wall of a vein is proportional to the height of the column of blood above it. This pressure is called Hydrostatic Pressure. Functioning valves limit hydrostatic pressure by separating the columns of blood. Nonfunctioning valves allow a very high column of blood to push out on the wall of the vein due to gravity.   

The pressure on the wall of a varicose vein increases the further down the leg, much like the pressure increase seen in deep sea diving. This ongoing pressure is like a snowball rolling down a hill as the more the valves are pulled apart, the more likely the vein will continue to stretch and enlarge over time under this pressure.

The Greater and Lesser Saphenous Veins are the main superficial veins of the lower extremity. The vast majority of lower extremity varicosities arise from the Greater Saphenous system. Lesser Saphenous varicosities are much less common.

If the Greater Saphenous Vein becomes stretched (typically in pregnancy due to increased circulating blood volume (25%), increased pelvic pressure and weight gain) the valves become pulled apart creating a leak and further increased pressure. This increased pressure eventually extends into the branches of the Greater Saphenous Vein causing dilation and visible varicosities.

Varicosities can cause multiple problems. Mild to moderate varicosities usually remain asymptomatic. More significant varicosities with considerable pressure can cause skin discolouration, pruritus ( itch ), leg swelling, discomfort and superficial thrombophlebitis (clotting). Over time the associated skin damage can progress to skin breakdown resulting in ulceration.

Varicose veins of the lower extremities are non-functional veins and can be treated safely to deal with both cosmetic and symptomatic problems.