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Abstract-Pressure ulcers are generally associated with external pressures exceeding internal capillary pressures over bony prominences when the body cannot initiate motor movement to change positions. This investigation evaluated microstructural changes occurring in human skin, in vitro, exposed to static versus cyclic pressures, simulating those recorded for heels of human subjects on various pressure-relief mattresses. Morphological data are reported for tissues exposed to pressure in a bench-scale loading system. Dynamic (cyclic-relief) pressure induced parallel alignments of connective tissue collagen bundles, which themselves became differentially oriented to various degrees perpendicular to the surface of the tissue. Static pressure, with no relief, invariably produced alignment of the collagen bundles of the connective tissue parallel to both one another and to the compressed tissue surface. The precursor to pressure ulcer formation may be microstructural alignment in response to the pressure conditions on tissue.
Key words: bedsore, collagen, decubitus ulcer, elastin, presure, pressure ulser, skin.
INTRODUCTION
This research evaluated the microstructural effects of static versus cyclic normal pressures on human skin. Results from the microstructural analyses of control specimens were compared with results for specimens from static and dynamic pressure experimental groups.
Prevention of pressure ulcers might be more effective if the earliest pressure-induced microstructural defects can be identified. Pressure ulcers have been defined simply as "localized areas of cellular necrosis" (1). The etiology of pressure ulcers is multifactorial; however, a major factor is external pressure exceeding internal capillary blood pressure. If capillary blood flow is obstructed for an extended period by such external pressures, one can presume that the resulting ischemia leads to the critical tissue damage that initiates the pressure ulcer (2). There is a reported, inverse relationship between the magnitudes of applied normal-to-surface forces and the amounts of time required for irreversible tissue damage to occur (3).
Pressure ulcers occur most often over bony prominences covered only by a small amount of muscle and subcutaneous tissue (4,5). The tissue interface "pressure" at such sites is conventionally measured as the normal force applied over the area of the specific sensor; it is seldom explicitly recognized that at a constant force (such as a patient's own weight), the pressure can significantly increase as the area of actual support decreases. Thus, pressures at bony prominences are high because...