elastic hosiery

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Elastic Hosiery

Elastic hosiery is prescribed for a number of conditions including:

Prevention and treatment of varicose veins and legs
Control of oedema

The circulatory system and the structure of blood vessels

The blood travels:

Around the body in the systemic circulation
To the lungs and back in the pulmonary circulation

Arteries and veins are composed of three layers:

Tunica adventia This layer is the outermost layer of the vessel and forms a connective tissue sheath. This sheath helps to stabilise and anchor the vessel by the blending of connective tissue fibres into adjacent tissue. In veins, the tunica adventia is generally thicker than the tunica media.
Tunica media This layer consists of involuntary muscle, which is stimulated by sympathetic nerve fibres, and elastic fibres. It is responsible for the change in lumen size of the vessel, and is very thick in arteries. In vasodilation, the muscle is relaxed and the vessel open. In vasoconstriction, the muscle contracts, and the vessel narrows. Collagen fibres within the tunica media bind it to the tunica adventia and tunica intima.
Tunica intima This layer is comprised of a smooth lining of endothelial cells, which also forms the valves, and a basement membrane.

Blood vessels are designed in such a way as to function effectively in their specific roles (see Figure 1)

Capillaries are comprised of a single layer of cells, and so allow the easy passage of oxygen and nutrients into the surrounding tissue.
Arteries have very thick muscular walls, enabling them to cope with the high-pressure surges of blood from the heart.
Veins have loose, slack walls as the blood in them is under very little pressure.

Venous return

Three input mechanisms are involved in the return of the venous blood to the heart:

The respiratory pump.
The venous pump.
Venous valves.

The respiratory pump

The thoracic cavity expands as a person inhales and the pressure within the pleural cavities is reduced. This drop in pressure causes air to be pulled into the lungs. At the same time, blood is also pulled from the smaller veins of the abdominal cavity and lower body into the inferior vena cava and right atrium. During exhalation, the thoracic cavity is decreased in size. Thus the internal pressure is caused to rise. Air is forced out of the lungs, and venous blood pushed into the right atrium.

The venous pump

The pressure of the blood in the leg veins (see Figure 2) results from the weight of the blood itself and is highest at the lowest point. When an individual is standing still, the pressure of the blood in the deep veins of the foot is approximately 90mmHg. This pressure is much lower in the superficial veins and capillaries. During normal standing and walking, the venous pump assists venous return. As the calf muscles contract, they compress nearby blood vessels propelling blood towards the heart. During muscle relaxation, the vessel once again fills with blood and the cycle is repeated during the next contraction. When a person is standing still for a long period of time, the venous pump does not operate and blood pools in the legs.

Venous Valves

The valves, present in leg veins, play a crucial role in the efficiency of the venous pump. They allow blood to flow in one direction only, and prevent it from flowing back towards the capillaries. Without valves, the effects of gravity when standing upright would cause pooling of blood in the leg veins. The blood is compartmentalised by valves. Therefore, the weight of the blood is divided between each of the compartments in the vein. Movement in the surrounding skeletal muscle squeezes the blood towards the heart. When standing, very fast cycles of contraction and relaxation occur within the leg muscles, the contractions pushing the blood towards the heart. When lying down, the heart and major vessels are at the same level. Therefore, venous valves have much less impact on venous return. The valves in the perforator connecting veins have the most important role. If these valves fail to work effectively, the high pressure in the deep veins, is transmitted to the much weaker, unsupported superficial veins. These veins become distended and tortuous (varicose veins). Capillary pressure becomes increased, and fluid is forced out into the extravascular space. This can then progress onto chronic venous insufficiency characterised by oedema, pigmentation, eczema, and ulceration of the leg.

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