Simulação da transferência de calor na articulação do joelho em modelo animal para condições de aquecimento e resfriamento

Abstract

Therapeutic application of heat and cold is commonly used in physical therapy, being relevant to the treatment of lesions of the muscular and skeletal systems (bones, ligaments, muscle and tendon). However, for the benefits of this therapy to be achieved, it is necessary for the therapeutic target to be heated or cooled within specified temperature limits. Correct assessment of tissue temperature is therefore an important strategy for safe and effective treatments, given that temperatures outside the recommended range can either not be sufficient for promoting the desired therapeutic effects or can cause thermal damage to the tissue. Numerical simulation is a promising alternative for the evaluation of temperatures in tissue layers exposed to different thermotherapy interventions. Thus, this study aimed at the simulation of the transient heat transfer taking place in the canine knee joint, resulting from the application of therapeutic heat and cold. The simulations were performed approaching the geometry of the knee by a cylinder (one-dimensional simulation) and considering the real geometry variations in the radial direction (two-dimensional simulation). Transient heat transfer in the canine knee joint was evaluated, with the effects of blood perfusion and metabolic heat based on the model proposed by Pennes. To solve the problem, software based on the finite element technique was used (FEHT). Two different boundary conditions were evaluated for therapeutic heating: 1 surface temperature equivalent to that of a thermal blanket (57.6°C) (simulation TU and simulation TB) and 2 heat flux of thermal blanket (215,7 Wm-2) (QU simulation and simulation QB). The tissue cooling was simulated considering the surface temperature equivalent to that of an ice pack (4.5°C). The results obtained were compared to experimental data available in literature. Among the one-dimensional simulations performed, simulation TU and cooling simulation showed average differences above 5%. In contrast, the simulation QU provided a good approximation to the experimental data, and the largest average difference found was only 3% (synovial liquid). In two-dimensional simulations, only the simulation TB showed average difference higher than 5%. The simulation QB showed a good approximation to the experimental data and the largest average difference found was 1.9% (cruciate ligaments). Although the cooling simulation have shown less than 5% error, through the isolines of temperature it was possible to visualize the tissues underlying the epidermis had temperatures lower than recommended (T <10 ° C). In summary, the simulations performed with the software FEHT were valid to assess and understand the temperature distribution in biological tissues during the processes of heating and cooling treatment. The simulations can be an important tool for noninvasive evaluation of the effectiveness of thermal treatments.