Thermodynamic Effect on Dermal Layers Following Defibrillation of Heart

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Much research and experimentation has made ventricular defibrillation a very well-studied process in terms of quantifying its effects on the heart. Yet, few researchers have looked into the potentially severe burning on the skin that can result from defibrillation. Because many have overlooked this problem, we chose to model the effects of defibrillation on the skin. The elimination of this painful side effect is an opportunity for design optimization. The following report illustrates our two goals: the development of a method to quantify the dermal burning associated with defibrillation, and the development of a better design for modern defibrillators to reduce dermal burning. We accomplished our first design objective by measuring the variation of three quantities over time in our model: the applied voltage, the heat conduction through the skin due to resistive heating, and the amount of thermal injury in the skin as a result of this heat conduction. This required us to couple three physics in COMSOL: conductive media physics to incorporate the voltage equation, heat conduction physics, and the diffusion equation (to quantify the burn by treating thermal injury as a zeroth-order diffusion problem). In order to accomplish our second design objective, we used our model to vary the thickness of the gel applied on the skin prior to defibrillator to determine if a higher gel thickness would result in less thermal injury in the skin layers. Through this process, our first design objective was satisfied by considering burning to occur in regions where the thermal injury concentration was greater than 0.53. In imposing this threshold, we found that first degree burns do occur on the skin, on areas of the epidermis right beneath where the defibrillator paddles are placed. We also used temperature to quantify the burn, finding that the skin temperature in the burning regions initially increased with time due to the conduction of heat from the epidermis, and then decreased with time due to the conduction of heat to other areas of the skin. For our second design objective, we found that the gel layer thickness reduced the maximum temperature from 328K at a 0.5mm gel thickness, to 316K at a 1.5mm gel thickness. As the thickness of the gel layer was increased, the patient’s burns became significantly less severe, with a maximum concentration of 1e5 with a 0.5mm gel thickness, and a minimum concentration of close to 0 with a 1.5mm gel thickness. Therefore, we found that the gel applied prior to defibrillation is pivotal in preventing cutaneous burns. Future work then includes customized settings for the age of the patient, skin type of the patient, and type of gel applied, all of which are parameters that can be easily adjusted in our model.
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2010-05-21T18:23:36Z
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