Why Do Varicose Veins Occur?

Veins are thin-walled blood vessels that carry blood from the body tissues back to the heart. Varicose veins occur when some of the valves between the deep and superficial veins of the leg no longer function properly.

There are two principal systems of veins in the body:

1. Deep veins, which lie among the muscles and carry about 90 percent of the blood.

2. Surface -or superficial- veins, which are often visible just under the skin. Surface veins do not have the protective muscular surrounding of deep veins. This means they are weaker and more likely to become varicose.

Surface veins carry blood from the skin and surface areas into the deep veins via connecting channels called perforator veins.

Here is how blood is moved from the legs toward the heart:

• The leg muscles squeeze the deep veins, forcing the blood upward.

• The veins are equipped with "one-way" valves to keep the blood from flowing backwards.

• As the blood is forced upward, the valves open to allow the blood to pass.

• After each heartbeat, the valves close momentarily to prevent back-flow.

When a valve between these two systems fails, blood can flow the wrong way because the pressure in the deep veins is greater than in the superficial veins.

• Instead of taking the blood from the surface veins, the deep veins may actually be pumping blood back into the surface veins.

• This increases the pressure within the surface veins.

• As blood pools in the surface veins and the pressure within these veins increases, more and more valves begin to deteriorate.

• Over a period of time, perhaps years, one valve after another fails.

• Where this happens, the surface veins swell from the excess blood and high pressure, creating varicose veins.

Why Do Valves Fail?

It is not known exactly why the valves fail. But it is thought they fail for the following reasons:

• There may be an inadequate number of valves, or the valve may be defective.

• The vein walls may be weak. Veins with weak walls bulge and damage the valves by pulling the delicate leaves of the valves apart.

• Valves may be damaged by blood clots. Although the clot dissolves, valves may become scarred. These damaged valves then fail to operate properly.

• In some cases, the vein itself may be at fault. Excessive pressure on a leg vein-caused by such factors as obesity, pregnancy, or periods of prolonged standing-causes the walls of the vein to bulge. When this happens, the two halves of the valve are forced too far apart to provide a complete blockage during the closing phase. Thus, some blood is allowed to flow downward.