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The veins in your leg are the return part of the circulation carrying blood back up the leg towards the heart. There are two main types of veins:

Superficial: - these are the visible surface veins under the skin more prominent when standing up.

Deep: - these are within the muscles of the leg and cannot be seen.

If the legs are below the level of the heart, for example when sitting or standing, the veins need to carry blood upwards against gravity. In order to do this they contain a series of one - way VALVES. The muscles in the leg are also involved. During walking, which is particularly good for venous problems, the calf muscles squeeze the deep veins increasing the flow up out of the leg. This reduces the pressure in the veins. Since the deep and superficial veins are connected the benefits of this are felt in all veins of the leg. Standing still has the opposite effect, raising pressure in the veins and reducing flow.

Once "varicose" the valves in the superficial veins do not work and the flow follows gravity, refluxing down the varicose veins when standing (see diagrams below) This is why the pain and swelling due to varicose veins is often worse after standing or at the end of the day.
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NORMAL FUNCTION AND ANATOMY OF LEG VEINS.
ANATOMY
Many of the surface veins are connected together as a network. There are two important places where this network drains into the deeper veins, one in the groin and one behind the knee. Drainage up to the groin is usually via the LONG SAPHENOUS VEIN (LSV) and behind the knee via the SHORT SAPHENOUS VEIN (SSV). See diagrams below. These veins often have faulty valves, allowing reflux in the wrong direction into varicose veins. Treating this source of faulty flow is a key part of dealing with varicose veins. Many of the treatments now available aim to either remove or block off these veins so that the abnormal flow is stopped. In general there are plenty of other veins in the leg working normally to maintain good circulation after the varicose veins have been treated. It is important to establish this before treatment, especially the state of the important deep veins of the leg.
Long Saphenous Vein Anatomy (left) and Short Saphenous Anatomy (right).
INVESTIGATIONS
After a clinical examination, a number of tests can be used to give more information about how the veins are working.
DOPPLER EXAMINATION
The simplest test is a doppler examination (see picture). This is a small hand-held machine that detects blood flow within the veins. The specialist examining you can listen over specific veins and using specific manoeuvres assess whether the valves in the veins are working. The first method is to squeeze the calf whilst you are standing. This causes blood to flow up the veins but when the squeeze is released the valves should stop any flow back down the leg. If there is flow heard after the squeeze is released this suggests that the valves are "leaky" causing "reflux". The second manoeuvre is to ask you to hold your breath and push down whilst lying on the examination couch. This is called a valsalva manoeuvre and raises the pressure in the veins. Normally the valves in the veins would prevent this raised pressure from causing any flow, but again, flow may be heard by the doppler machine if the valves are "leaky".
DUPLEX ULTRASOUND SCAN
The next step on from a doppler examination is an ultrasound scan of the veins (see picture above). This combines the dopplers' ability to detect blood flow with ultrasound pictures of the veins. This enables a "map" of the leg veins to be drawn highlighting all the areas where there are faulty valves (see picture below). In addition any abnormal clot within the veins can be seen indicating a thrombosis. These scans are called Colour Duplex scans, and are probably the best way to investigate leg veins at the present time.
Charts and diagrams showing the direction of flow based upon the ultrasound findings.
VENOGRAM
Dye can be injected into the veins in order to show up the veins on X-ray. This used to be a common method of looking at veins but has largely been replaced by Duplex ultrasound.
Venogram showing the veins (in black) behind the knee and in the calf. The vein is not seen higher up because it is occluded with clot (see thrombosis section)
MR SCAN
Modern magnetic resonance scanners can give very good images of veins in the leg but are more complicated to perform than ultrasound. Sometimes this is a useful way to image the veins.
MR Venogram of abnormal calf veins.
PLETHYSMOGRAPHY
The function of the veins in terms of their effect on blood flow, the volume of blood in the leg, and the pressure in the veins can be measured by a variety of other techniques including plethysmography. These more precise measurements of venous function are sometimes useful but are more often used in research projects.
Venous Ulcers
Thrombosis, PTS & Phlebitis