Venous hypertension: calf muscle pump failure and its effects
Venous hypertension is raised pressure within the leg veins, which can result from failure of the calf muscle pump (calf muscles squeezing the deep veins to force blood upwards).
Remember
When the calf muscles stop pumping, as in someone who is immobile, blood pools in the leg veins and the pressure stays high, which causes oedema and can lead in time to skin damage.
Memory aid
the calf is the second heart of the leg
When the calf stops pumping, the pressure rises behind it.
The calf muscles act as a pump for the leg veins. Each time the calf muscles contract, they squeeze the deep veins and push blood upwards towards the heart, while one-way valves stop it falling back.
If this calf muscle pump fails, blood builds up in the leg veins under higher pressure. That raised pressure is called venous hypertension, and it is not the same as high blood pressure in the arteries. The pump can fail, for example, in someone who is immobile or who walks with a shuffling gait (very small steps that barely use the calf). The other common cause is incompetent valves, which let blood leak backwards and pool.
Pressure that stays high inside the leg veins forces fluid out of them and into the interstitium, the small spaces between the cells of the tissues. The fluid collects as oedema, visible swelling that is usually the earliest sign, so patients notice swollen ankles and lower legs.
If the pressure stays high, the leaking fluid can inflame the skin. Red blood cells leak out too, and their breakdown leaves iron deposits that stain the skin brown. In time the skin can show varicose eczema (itchy, scaly skin), lipodermatosclerosis (inflammation and hardening of the fat under the skin) and eventually a venous ulcer, where the skin breaks down. Blood that stays in the veins is also more likely to clot, which raises the risk of deep vein thrombosis.
Key facts
- Normal pump
- the calf muscles squeeze the deep veins in the calf when they contract, which pushes blood upwards towards the heart.
- Failure of the pump
- it can follow immobility or a shuffling gait, because the calf muscles then hardly contract.
- Earliest sign
- oedema, from fluid forced out of the veins into the interstitium, is usually the earliest sign.
- Skin changes
- the raised pressure inflames the overlying skin, which can lead to varicose eczema, lipodermatosclerosis and eventually leg ulcers.
- Brown staining
- red blood cells that leak into the skin break down and leave iron deposits that stain it brown.
- Clot risk
- blood that stays in the veins is more likely to clot, so venous stasis (blood staying put in the veins) raises the risk of deep vein thrombosis.
Exam traps
- Narrowed arteries reduce the blood delivered to the leg, but they do not impair the return of blood through the veins, so they do not cause venous hypertension.
- Blocking the lymphatic system, a separate network of vessels that drains tissue fluid, causes lymphoedema (swelling from retained lymph) but does not raise the pressure in the veins.
- Oncotic pressure, the pull of plasma proteins that draws fluid back into the capillaries, would hold fluid in the vessels rather than draw it out, whereas in venous hypertension the high pressure inside the veins pushes fluid out.
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