NORMAL FUNCTION OF LEG VEINS AND HOW VENOUS FUNCTION IS INVESTIGATED.

The veins in your leg are part of the circulation carrying blood 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.

The veins need to carry the blood upward against gravity when we are standing. In order to do this they contain 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.

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). 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. 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.

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.

MR SCAN

Modern magnetic resonance scanners can give very good images of the larger veins at the top of the leg and in the pelvis. Sometimes this is a useful way to image the 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.