Peripheral Vascular Disease

The aorta, which is the main artery from the heart enters the abdomen and after giving off branches to the kidneys and the gut divides into two. These are called the common iliac arteries; they pass through the pelvis and eventually become the main artery supplying each leg. The arteries supply the oxygenated blood from the heart to the tissues. In the leg much of this supply is to the hard working muscles of the leg. At rest only 2% of the blood from the heart goes to the muscles of the leg but this can increase to 20% when you exercise in the form of walking or running.

Atherosclerosis is a disease of the arteries in which plaque (atheroma) can build up in the walls of the arteries and cause them to narrow (stenosis) or even totally occlude (blocked arteries). This condition occurs more often and rapidly in people who smoke, have high cholesterol, high blood pressure or diabetes but also is a part of the normal aging process. Any artery in the body can be affected and in fact the leg arteries are one of the more common group of arteries to be affected by this process. When atheroma builds up in the arteries that supply the legs the consequence of this depends on several factors.

As a narrowing or occlusion occurs in one of the two main arteries of the leg after a small branch or branches of the artery above the process will enlarge and connect up with branches below the blockage. These new arteries are called collaterals Often these collaterals supply the leg with enough blood that no symptoms occur. However more commonly although there is enough blood for a resting leg when you walk (and 60 times more oxygen is needed by your muscles) not enough oxygenated blood is delivered to the muscles and there is a build up of acid and symptoms of pain and tightness occur in the main muscle groups and you are not able to continue walking. This is called vasculogenic claudication ( from latin ‘cladio’ meaning to limp ). Often it is the calf muscles that are affected but the thigh or buttock muscles can also be affected.

A useful analogy is thinking of driving from Auckland to Hamilton. If it is the middle of the night and there are no traffic jams or road works and you drive straight down SH1 the trip takes only 90 minutes. If there are roadblocks and traffic jams and you are forced to take side roads (collaterals) then the trip can take much longer – you still get there (your leg is alive) but you miss out on some activity (walking) . The more areas of disease are involved, the more profound the symptoms. With vasculogenic claudication the typical picture is that you develop pain / tightening cramp in the calf after walking a certain distance and you need to stop walking. This usually makes the pain go away and you are able to keep walking again but the symptoms reappear at a similar distance. Your walking distance is often reduced walking uphill or into the wind.

If your only symptom is claudication your surgeon may simply advise you that you should undergo a progressive walking exercise programme. In this programme you are encouraged to walk for 40 – 60 minutes at least 4 times a week. You walk as far as you can then stop. When fully recovered you begin walking again and repeat the process. If you do this regularly enough, just like athletes with their physical training you can improve your walking distance often to the point where you can walk without any symptoms. The exact mechanism which leads to this improvement is unclear. Some experts consider that it promotes the formation of collaterals whereas others believe that the muscles themselves become more efficient at utilizing the limited amount of oxygen that they receive. Either way it works.

When the blood flow to the leg is severely limited (usually involving extensive atheroma at several levels) then more serious symptoms and problems can occur. In this situation the blood supply to the foot can be so poor that when the foot is elevated during sleep (without the benefit of gravity which improves blood supply) there is not enough oxygen now supplying the nerves in the foot and this leads to a severe burning / stinging pain that wakes you from your sleep. Often relief is obtained by hanging the foot over the side of the bed or getting up and going for a walk. These symptoms in this setting are called ischaemic rest pain.

Again if the blood supply to the foot is severely limited tissue loss (ulcers and gangrene) can develop. If you have rest pain or tissue loss then you have critical ischaemia. Unlike with claudication in the setting with critical ischaemia it is usually imperative that something is done to improve the blood supply to your legs. This is called revascularization of the leg.

Next: Investigations and Prognosis.