HEAT SPREAD IN TUBULAR STRUCTURES EXPOSED TO MONOPOLAR HIGH-FREQUENCY ENERGY: EXPERIMENTAL MODEL AND PROBLEMS OF MATHEMATICAL MODELING

Heat propagation inside tubular structures during electrosurgical units application is difficult to analyze without specialized equipment, so relevant information is scarce. The study provides description of the experimental bench for investigating thermal effects of monopolar devices on tubular structures and review of existing mathematical models of such tissue heating. The stent-like tube with Pt100 temperature sensors connected to microchip with noise filter was constructed. The experiment was performed on the isolated hepatobiliary system of six pigs of the same weight. A stent was placed in the common bile duct and cholecystectomy was performed. Surface temperature was registered by high-resolution thermal camera, electrosurgical unit was activated by a toroidal inductor. A literature review of methods for mathematical calculations of the effect of high-frequency current on biological tissues was conducted with relevant keywords in PubMed and Scopus. Heat reaches the hollow structures in 3-5 s after activation rises the ductal surface temperature to an average of 100-110°С while the surrounding adipose tissue and outer layers of its walls play a role of insulators, thus the temperature of the mucosal lining only rose to 50-55°С maximum. Identified mathematical models based on the Arrhenius and Pennes equations were accurate in prediction of temperature, but not of its distribution.