Análise das condições de contorno e dos termos da equação clássica de biotransferência de calor aplicada ao procedimento de crioterapia da articulação do joelho canino

Abstract

Non-pharmacological procedures are quite common in the treatment of injuries. Among the various techniques available, cryotherapy has been highlighted due to its efficiency when applied in certain lesions. In order for the treatment to occur properly it is important that the tissue temperature reach values within a recommended range. Knowing the temperature profile during cryotherapy is critical to ensuring the benefits of treatment. The methods available for temperature monitoring are invasive and often inaccurate. Thus, the heat transfer equation proposed by Pennes appeared as an alternative to determine the temperature considering the contribution of blood perfusion and metabolic heat generation. In this context, numerical simulations are important tools for solving the equations and determining the temperature profile of the tissues. In this work, numerical simulations of the application of cryotherapy in canine knee were performed. The main objective of this study was to present a proposal of the numerical model that best represents the therapeutic cooling. To perform the simulations, a geometric model representative of the cross section of the canine knee was used. The simulations were performed using the Ansys program and lasted 30 minutes, representing the duration of cryotherapy. In the simulations, the effects, in the temperature field, of the individual application, of three types of contour conditions were evaluated. The first one considered as a heat flow contour condition of -948.9 W / m² and a second condition contemplated the use of a function, the experimental temperature, applied to the epidermis. The contour condition that presented the best results was the second simulated condition with a mean percentage difference of 14.36%. When determining the ideal contour condition, simulations were performed to evaluate the different proposals of blood perfusion rate, and the third configuration considered the rate of perfusion constant. The fourth considered perfusion varying exponentially with tissue temperature, and the fifth configuration considered the perfusion varying exponentially with skin temperature. Simulations in which the perfusion rate was constant and varying exponentially with skin temperature obtained the lowest mean percentage difference values of 14.24% and 14.28%, respectively. In view of these results, simulations were carried out to evaluate the contribution of the term of metabolic heat generation varying with the temperature of the living tissue. The last simulations showed mean percentage difference values of 14.35% for constant perfusion rate and 14.39% for variable perfusion rate with skin temperature. Seven simulations were performed and the one that presented a good approximation with the experimental data was the one that adopted the temperature of the epidermis as contour condition, blood perfusion varying exponentially with skin temperature and constant metabolism. Seven simulations were performed and a good approximation was presented with the experimental data, in relation to the others, for a temperature of the epidermis as a contour condition, blood perfusion varying exponentially with a skin temperature and constant metabolism. However, new studies are needed in order to better represent cryotherapy by means of numerical simulation.