The Effect of Pressure Gradients on Perceived Discomfort

Introduction: A pressure gradient is where high and low pressure meet. It is responsible for displacement and irritation of the skin commonly caused by tight bandages, bracelets, or socks. The irritation is at the edge where the skin is displaced by the high and low pressure. An analysis of the effect pressure gradients have on discomfort would have significant medical relevance for any device, fixture, or clothing pressed against the skin at high pressure. This primarily includes prosthetic and orthotic devices. The bottom surface of the heel provides a naturally circular, uniform pressure profile. This makes it the optimal testing location for determining the relationship between artificially induced pressure gradients and discomfort with clinical relevance to foot ulcers. Methods: The IRB approved study consisted of Clemson University students. Participants pressed their heels along the edges of two materials pressed together. The materials varied in hardness and vertical height to induce different pressure gradients. For each set of materials, a Tekscan™ pressure sensor placed between the materials and heel measured an array of pressure. Participants rated their discomfort on a scale of 0-10. The materials were representative of orthotic inserts and consisted of four silicone molds of varying shore 00 hardness (41.3-87.4) and HDPE. Vertical displacement varied up to 3mm. There were 28 tests of varying hardness and height carried out in a random order. A force plate was placed below each heel to ensure participants applied consistent weight for each test. The pressure and discomfort data were compared directly through graphical analysis to determine the effect pressure gradients have on discomfort for the general population. Results: A comparison of different methods used to compare pressure gradients and peak pressure at the heel determined that a comprehensive measurement of all pressure gradients in the heel had the strongest correlation with discomfort.