Modelling of pressure ulcer (PU) risk prediction system

Human skin deformation occurs due to external loading. As a result, blood flow in soft tissue becomes low and also the oxygenation decreases. Tissue under continuous loading results in tissue necrosis and leads to pressure ulcer (PU), also known as bedsore, decubitus ulcer, and ischemia. The amount of external load applied to the body support surface is associated with a subject´s BMI (body mass index). Therefore interface pressure (IP) at the skin and the surface is the result of a subject´s physical and support surface properties. Interface pressure increases, the blood flow decreases and a subject starts developing stage-1 pressure ulcer. Previous research suggests that interface pressure of 32 mmHg (4.26 kPa) can cause PU, but there is no strong evidence to show at what time that pressure is reached. Also interface pressure changes from subject to subject due to their body compositions. Three risk assessment scales are available to predict overall risk of PU formation. But none of these scales take interaction of body support surface materials into account. Also these do not provide any information at which area a subject is at risk of PU formation. In this work a study is presented where external load at different bony areas are measured using 11 volunteers. By measuring the external load for 11 subjects (age:33 ± 7 yrs and BMI:25.04 ± 3.01 kg/m²) at different bony areas, the relationship with the total body weight was identified. A mathematical model is proposed to predict the risk of PU formation combining the Waterlow risk assessment scales for bony areas and a graphic user interface to predict this is discussed.