SKIN-RESPONSE TO REPETITIVE MECHANICAL-STRESS - A NEW EXPERIMENTAL-MODEL IN PIG

Objectives: To develop a new animal model for investigating the relati ons between interface stresses at the skin, adaptation, and breakdown. There were two hypotheses. (1) In skin subjected to varying types of repetitive mechanical stress, the tissue response depends on the direc tion and magnitude of the load. As the shear stress increases, tissue breakdown occurs earlier, (2) In skin subjected to repetitive mechanic al stress of longer duration, there will be evidence of tissue adaptat ion. Design: Multiple case control, single-blind. Interventions: Varyi ng combinations of normal and shear mechanical loads are applied to pi g's skin for short durations (breakdown studies) or longer durations ( adaptation studies). Main Outcome Measures: Gross evidence of breakdow n (visual inspection of skin) and microscopic changes (eg, histologic features of breakdown; thickness of epidermis and dermis; the length a nd shape of the basement membrane; concentration of inflammatory cells , mast cells, and fibroblasts; and quantity of elastin fibers). Result s: The instrumentation was reliable and a significant improvement over past models in that shear forces were delivered and measured in a con trolled manner. The animal model and tissue methodology provided consi stent results, and it was found that skin breakdown occurred earlier a s shear forces were increased. Evidence of tissue adaptation occurred in the long-term experiments, although corresponding morphologic chang es have been difficult to elucidate. Conclusions: To address the probl em of skin breakdown, new animal models are strongly needed to better understand basic biologic processes related to pressure ulcer developm ent. (C) 1998 by the American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation.