[Theoretical and practical bases of compression]

The pressure applied by rigid or elastic compression of the skin surface of a limb is exerted as a function of two parameters. Pressure applied by an elastic tissue acts according to Laplace's law, varying with the tension of the elastic tissue and the radius of the curve of the area compressed. A rigid dressing acts solely by alternating working and resting pressures. Superficial pressure is transmitted to the extra- and intra-fascial compartments through the intermediary of an increase in tissue pressure. This pressure extension acts on all the compressible structures of the limb. It reduces the caliber of the veins in all compartments, and therefore the total venous blood volume of the limb, and increases the rate of circulatory return. The venous pressure adapts itself to the pressure of the dressing. The action on the vessel wall is seen as an increase in fibrinolytic activity and the proliferation of contractile myocytes. Its principal effect, however, is on vascular-tissue integrity: it diminishes interstitial edema and compacts the connective tissue fibrils, decongests the capillary endothelium and reduces the pericapillary sleeve of mucopolysaccharides. But it increases basal membrane thickness. Too high a pressure provokes collapse of the lymphangions. The rheologic action of the compression results in a decrease in blood viscosity. The effect of the compression is to induce local reabsorption of venous edema, while lymphatic edema is displaced towards the root of the limb to a zone where it may be reabsorbed. All these phenomena are reversible on removal of the compression treatment.