A Synergistic Approach to Pressure Ulcer Prevention for Spinal Cord Injured Individuals through Experiments and Modeling

轮椅使用者一天中的大部分时间都坐在同一个座位上，并且通常具有有限的能力来调整他们在轮椅内的位置。这导致显著的高度局部化的应变，在臀部和大腿的组织中产生临界应力集中，导致血液灌注减少（即，通过毛细血管的血液输送）、组织损伤，并最终引发所谓的压力性溃疡（PU）。PU是疼痛的，深的伤口，可以穿透到骨头。他们的治疗可能需要住院治疗，如果感染，可能导致死亡。目前减少PU形成的努力是不够的，迫切需要更好的预防方法。轮椅及其垫子的设计会影响负载分布，从而影响深层组织上的应力和应变，从而影响血液到达这些组织的能力。具体地，在座椅的力学中需要考虑两种类型的载荷：正常载荷（即，垂直于皮肤的力），和剪切载荷（即，平行于皮肤的滑动力）。先前的工作表明：1）坐着的个体经历恒定剪切; 2）包括剪切力的负载条件比单独的正常力对血液灌注更有害; 3）内部组织应力集中降低灌注;以及4）灌注降低是导致PU的因素。然而，还没有研究探索如何定期重新分配力以促进血液灌注或量化剪切载荷对轮椅使用者深部组织的影响。通过结合严格的实验测试和计算建模的协同方法，PI将开发一种座椅系统，该系统包括用于减少剪切载荷的界面和可以将力从一个区域重新分配到另一个区域的铰接轮椅。这种座椅系统将导致臀部和大腿的灌注增加，从而降低PU形成的可能性。这项工作将通过减少PU的潜力对脊髓损伤患者产生直接影响，并将对平民和军事人群产生更广泛的影响。血液灌注和负荷在压疮（PU）的形成中发挥作用，但没有轮椅设计或缓冲设计专注于促进血液灌注或减少剪切负荷引起的深部组织应力。此外，没有先前的工作集中于量化剪切力对脊髓损伤患者的臀部和大腿中的深层组织的影响。在本项目中，PI将采用实验测试和理论建模相结合的方法：1）确定坐骨结节区域上的剪切力和血液灌注，作为坐姿中姿势变化的函数，2）确定臀部和大腿的体内有效刚度，3）进行有限元研究以设计优化的界面表面以使深部组织应力和应变最小化，以及4）制造和测试垫子/轮椅系统的患者专用原型。该项目的最终目标是开发一种座椅系统，该系统包括用于减少剪切载荷的界面和能够将力从一个区域重新分配到另一个区域的铰接轮椅。这种座椅系统将导致内部应力降低和灌注增加，从而降低PU形成的可能性。这项工作是高度创新的，因为它将是第一个与姿势和剪切力对血液灌注的影响，第一个模拟姿势对深部组织应力分布的影响。量化和定义力、姿势和灌注之间关系的能力是对PU形成相关科学进步和器械设计的重大贡献。了解力、姿势和灌注之间的关系对于改善PU形成的建模、座椅设计的进步以及预防PU是必要的。这项工作的影响将通过改进座椅设计来体现，这可能会导致PU减少。 这项研究将影响所有因受伤或疾病导致行动受限的人，包括卧床不起、老年人、经历过事故、中风或在服兵役期间受伤的患者。

Wheelchair users sit in the same seat for the majority of their day and often have limited ability to adjust their position within the wheelchair. This results in significant, highly localized strains yielding critical stress concentrations in the tissue of the buttocks and thighs, leading to reduced blood perfusion (i.e., blood delivery through capillaries), tissue damage, and ultimately the initiation of what is known as a pressure ulcer (PU). PUs are painful, deep wounds that can penetrate to the bone. Their treatment can require hospitalization and, if infected, can lead to death. Current efforts to reduce the formation of PUs are insufficient and there is a critical need for better prevention methods. The design of a wheelchair and its cushion impacts the load distribution, which affects the stresses and strains on the deep tissues, and consequently, the ability of blood to reach these tissues. Specifically, two types of loads need to be considered in the mechanics of seating: normal load (i.e., a force perpendicular to the skin), and shear load (i.e., a sliding force parallel to the skin). Prior work has shown that: 1) seated individuals experience constant shear; 2) loading conditions that include shear forces are more detrimental to blood perfusion than normal forces alone; 3) internal tissue stress concentrations decrease perfusion; and 4) decreased perfusion is a factor that leads to a PU. No work has been done, however, to explore ways to periodically redistribute forces to promote blood perfusion or to quantify the effects of shear loading on deep tissues for wheelchair users. Through a synergistic approach that combines rigorous experimental testing and computational modeling, the PIs will develop a seat system that incorporates an interface surface for reduction of shear loads and an articulating wheelchair that can redistribute forces from one region to another. This seat system will result in increased perfusion in the buttocks and thighs, therefore decreasing the potential for PU formation. The proposed work will have an immediate impact on patients who have a spinal cord injury through the potential for PU reduction, and will have broader impacts for civilian and military populations.Both blood perfusion and loading play roles in the formation of a Pressure Ulcer (PU), however there is no wheelchair design or cushion design that focuses on promoting blood perfusion or reducing deep tissue stresses caused by shear loads. Moreover, no previous work has focused on quantifying the effect of shear forces on the deep tissues in the buttocks and thighs of spinal cord injured patients. In this project, the PIs will employ a combination of experimental testing and theoretical modeling to: 1) determine the shear forces and blood perfusion on the ischial tuberosity region, as a function of postural changes in seated positions, 2) determine effective stiffnesses in-vivo of the buttocks and thighs, 3) conduct a finite element study to design optimized interface surfaces to minimize deep tissue stresses and strains, and 4) manufacture and test a patient-specific prototype of a cushion/wheelchair system. The ultimate goal of this project is to develop a seat system that includes an interface surface for reduction of shear loads and an articulating wheelchair that can redistribute forces from one region to another. This seat system will lead to decreased internal stresses and increased perfusion, therefore decreasing the potential for PU formation. The work is highly innovative in that it will be the first to relate the effects of posture and shear forces on blood perfusion and the first to model the effects of posture on deep tissue stress distribution. The ability to quantify and define the relationship between force, posture, and perfusion is a significant contribution to the advancement of science related to PU formation and for device design. Understanding the relationship between forces, posture, and perfusion is a necessity for improved modeling of PU formation, advances in seating design, and imperative to the prevention of PUs. The impact of this work will be seen through improved seat designs that are likely to lead to PU reduction. This research will impact all individuals who have an injury or disease causing limited mobility, including patients who are bedridden, elderly, have experienced an accident, stroke, or injuries incurred during military service.