The production and measurement of sub-bandage pressure: Laplace's Law revisited.

OBJECTIVE The present study was undertaken to demonstrate that the pressures produced by multiple layers of compression bandages applied to artificial limbs of known circumference with predetermined levels of tension can be predicted accurately using the modified Laplace equation. METHOD Up to four layers of different bandage types were applied in a carefully controlled fashion to cylinders of known circumference, with tensions ranging from around 200-2000 grams/10cm width. The pressures generated were measured using pneumatic pressure sensors previously shown to possess the required degree of accuracy for this type of experimental system. RESULTS Good correlation was observed between the mean and standard deviation of each pair of experimental and calculated pressure values for all combinations of bandage type, application tension and cylinder circumference. Over the clinically relevant range of pressures, the difference between data sets was generally less than 1.0mmHg. CONCLUSION The results of this experimental study unequivocally prove that provided accurate values for all the relevant variables are known, it is possible to predict the pressure that will be developed by a compression bandage on a limb of known size. However, it is important to recognise that other factors such as the elastomeric properties of the fabric will have a major effect upon the ability of a bandage system to sustain initial compression values. Furthermore, the variation in radius of curvature around a limb will mean that point pressures readings recorded at individual locations around the circumference may vary dramatically from the average value predicted by the modified Laplace equation, calling into question the value of sub-bandage pressure measuring devices for this application.