The Effects of Age and Peripheral Vascular Disease on the Circulatory and Mechanical Response of Skin to Loading

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Abstract
The skin and subcutaneous soft tissues of amputation residual limbs are required to withstand externally applied loads of greater magnitude than similar tissues of the intact lower limb. Increased age and poor circulatory status may contribute to the increased risk of tissue injury seen in this population. This study evaluates the effects of age and circulatory status as risk factors for skin injury resulting from externally applied forces. Twelve young control (YC), six elderly control (OC) and 11 subjects with peripheral vascular disease (PVD) were studied. After base-line ankle arm index (AAI) measurements, TcPO2 electrodes were applied 10 cm below the knee over the medial surface of the tibia and the muscle belly of tibialis anterior. TcPO2 measurements and tissue displacements were obtained under the influence of incremented, normally oriented, external loads. The sensitivity of the tissues to applied loads was determined by calculating the load at which the TcPO2 reached zero. The stiffness of the tissues (displacement/load) was calculated under high (>40 mm Hg) and low (<20 mm Hg) loading conditions. No difference was noted in tissue sensitivity to applied loads between the OC and YC populations. The TcPO2 decreased to zero in the PVD population at significantly lower applied loads than both the OC and YC populations. The tissue stiffness of the PVD and the OC populations over bone was greater than the YC population, but no significant differences were noted between the PVD and the OC populations. In summary, increased age does not result in a greater tissue sensitivity to externally applied loads, in spite of the demonstrated increased tissue stiffness. That is, increased age alone does not appear to contribute to an increased risk of pressure injury to the skin. Arterial PVD however, may result in a greater sensitivity to externally applied loads, and therefore, greater risk of pressure injury.

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