The objective of this paper is to provide a definition for interface compression that uses essential principles of engineering science. This definition discusses factors that influence the amount of applied pressure, including the size of the limb, the amount of fabric tension (graduated pressure profile), the number of layers, and the material creep characteristics. Laplace's law has been applied to compression therapy. Tension-extension profiles have been derived for different types of compression fabric to demonstrate the effects of resistance and friction. Force-time profiles have been derived for different types of fabric compression systems to demonstrate the effects of creep (creep is defined generally as the irreversible deformation of a material over time in the presence of a constantly applied load). Here, the fabric compression systems were applied to a test-bed that supplied a constant force to the fabric; creep was taken as the loss of compression (pressure) over time. Laplace's law has been interpreted for compression therapy. The amount of fabric tension is determined by the extent to which it is stretched during application, as well as by changes in the size of the limb. The fabric's relative elasticity, which is quantified by the rigidity index and is related to the slope of the tension-extension profile, dictates the amount that the applied force changes with extension. Compression systems that use multiple layers of fabric are generally more resistive to stretching than single-layer systems. Friction acting between the layers, as well as the added force from each layer, serves to increase the overall compression of these systems. As the applied force rises, the amount of pressure supplied by the fabric increases. However, when the same force (or fabric extension) is used, the applied pressure is less when distributed over a larger surface area. In other words, as the circumference of the limb increases, the pressure decreases. This is the driving principle behind graduated compression. In addition to the changes in fabric tension resulting from extension, the creep characteristics of the material affect the amount of compression provided throughout the wear cycle. The factors influencing interface compression are multi-faceted. Based upon the interpretation of the material properties of compression fabrics (tension-extension profile, number of fabric layers, and creep), new therapeutic guidelines have been established, and others clarified.
Declaration of interest: This study was sponsored by Carolon. L. Reid, and S. Kravitz are employees of Carolon and E. Grant is a Member of the Board. M. Hegarty-Craver and C. Kwon have received monetary compensation as researchers for Carolon.
Keywords: Laplace's law; compression hosiery; compression therapy; multilayer bandage systems.