The physics of sub-bandage pressure measurement

Compression therapy is the principal treatment for leg ulcers associated with venous disease. The extent of compression generally can be estimated from the general Laplace equation relating pressure, bandage tension and leg radius. This study aimed to investigate the physical forces under long stretch bandages applied under constant tensions to cylinders of three defined radii ('model limbs'). Force expressed as pressure was measured under one, two and three layers of eight long stretch bandages and a plastic film (control) using temperature-compensated, strain-gauge pressure transducers. The bandages were applied at the manufactures' recommended extensions/tensions and at constant tensions (2-10N) to three rigid plastic tubes of increasing size, covered with a layer of soft foam. Foams of different hardnesses ranging from 20 to 230N were assessed. The median applied pressure and observed bandage characteristics changed with bandage type. The median applied pressure also changed with tension, number of layers, tube radius and foam hardness. The inter-layer shear component also tended to increase with the number of layers. An increase in sub-bandage pressure was observed relative to the radius, tension, foam hardness and number of layers but the relationship was not directly proportional. The shear force tended to be associated with increased bandage layers.