The Effects of Pressure and Shear on Capillary Closure in the Microstructure of Skeletal Muscles: Computational Studies

Deep tissue injury (DTI) is a serious and potentially deadly type of pressure ulcers, which initiate in deep muscle tissue under bony prominences of immobilized patients, and progress outwards towards the skin with no clear visual indications of the injury at the surface of the body. It had been suggested that DTI appear in muscle tissue first, due to the dense capillary vasculature in skeletal muscles which is susceptible to obstruction and occlusion by mechanical forces [1–3]. Though mechanical forces may cause capillaries to collapse and thus induce ischemic conditions in adjacent muscle cells [2], some investigators stipulated that ischemia alone cannot explain the etiology of DTI, and so, other mechanisms, particularly excessive cellular deformations must be involved [1]. We hypothesize that physiological levels of stresses and strains in muscle tissue under bony prominences — even when muscles are highly loaded as during sitting — do not cause complete closure of muscle capillaries, and therefore, do not cause an acute ischemia in muscles. If this is indeed the case, then ischemia cannot be the only factor contributing to DTI onset. In order to test our hypothesis, we developed a finite element (FE) model of the microstructure of skeletal muscle, at the level of muscle fascicles, and employed the model to determine the stress and strain levels required for causing partial and complete closure of capillaries.