Lateral pressure equalisation as a principle for designing support surfaces to prevent deep tissue pressure ulcers

When immobile or neuropathic patients are supported by beds or chairs, their soft tissues undergo deformations that can cause pressure ulcers. Current support surfaces that redistribute under-body pressures at vulnerable body sites have not succeeded in reducing pressure ulcer prevalence. Here we show that adding a supporting lateral pressure can counter-act the deformations induced by under-body pressure, and that this ‘pressure equalisation’ approach is a more effective way to reduce ulcer-inducing deformations than current approaches based on redistributing under-body pressure. A finite element model of the seated pelvis predicts that applying a lateral pressure to the soft tissue reduces peak von Mises stress in the deep tissue by a factor of 2.4 relative to a standard cushion (from 113 kPa to 47 kPa)—a greater effect than that achieved by using a more conformable cushion, which reduced von Mises stress to 75 kPa. Combining both a conformable cushion and lateral pressure reduced peak von Mises stresses to 25 kPa. The ratio of peak lateral pressure to peak under-body pressure was shown to regulate deep tissue stress better than under-body pressure alone. By optimising the magnitude and position of lateral pressure, tissue deformations can be reduced to that induced when suspended in a fluid. Our results explain the lack of efficacy in current support surfaces and suggest a new approach to designing and evaluating support surfaces: ensuring sufficient lateral pressure is applied to counter-act under-body pressure.

当行动不便或神经病变患者依靠病床或轮椅支撑时，其软组织会发生变形，进而引发压疮。当前用于在身体受压薄弱部位重新分布体压的支撑界面，未能有效降低压疮的发病率。本研究表明，施加辅助侧向压力可抵消体压引发的软组织变形；相较于当前基于体压重新分布的干预方案，这种“压力均衡化”策略在减少压疮诱发性变形方面效果更优。我们通过坐姿骨盆有限元模型（finite element model）预测，相较于标准坐垫，对软组织施加侧向压力可使深部组织的峰值冯·米塞斯应力（von Mises stress）降低2.4倍（从113千帕降至47千帕），其效果优于采用更贴合的坐垫（仅能将冯·米塞斯应力降至75千帕）。同时采用贴合型坐垫与侧向压力方案，可将峰值冯·米塞斯应力进一步降至25千帕。研究表明，峰值侧向压力与峰值体压的比值，相较于单纯依靠体压调控，能更有效地调节深部组织应力。通过优化侧向压力的大小与施加位置，可将软组织变形程度降至类似流体悬浮状态下的水平。本研究结果阐释了当前支撑界面疗效不佳的原因，并提出了设计与评估支撑界面的全新思路：确保施加足够的侧向压力以抵消体压带来的影响。