Investigation of Electrosurgical Tissue Joining.

This dissertation analyzes how the bipolar electrosurgical vessel sealing process is affected by changes in the tissue thermal conductivity, water content and applied compressive load. Bipolar devices apply electrical energy to the tissue, causing resistive heating and the proteins to denature. This heating causes the tissue temperature to rise and damage may occur in the surrounding tissues and nerves. Therefore, a better understanding of the key tissue properties and how they affect the sealing process is needed. This will allow for the development of improved electrosurgical devices that are able to minimize thermal spread, while still maintaining a quality seal. Using a thermistor-based measurement technique, experimental results show that reducing tissue water content and compressing tissue reduces the tissue thermal conductivity. A three-phase Maxwell-Eucken model was applied to predict the thermal conductivity of the tissue. Experimentally measured temperature profile analysis of bipolar electrosurgical sealing of in vivo femoral and mesenteric artery vasculature was also conducted. The temperature profile, electrical voltage and current were analyzed to predict changes in tissue impedance and water content during vessel sealing. As water was lost from the tissue, the tissue impedance increased and the change in tissue temperature per pulse was reduced. A finite element model (FEM) was developed to predict the thermal profile in the vessel during sealing. The discrepancies between the experimental and modeling results are discussed. The need to include mass transfer in the FEM is identified. The compressive force acting on the vessel during sealing was measured and related to the applied handle force. Experimental tests were conducted to examine the effect of the compressive force on the burst pressure at four different force levels. The two higher compressive forces significantly increased the burst pressure of the vessel seals. Novel experimental methods were developed to determine the tissue temperature profile and thermal spread, as well as the effect of compressive force on the seal quality. A better understanding of the tissue thermal properties can improve the tissue temperature profile prediction during FEM. To further improve the quality of the vessel sealing process, real-time force monitoring can be used.PhDMechanical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/77827/1/chazz_1.pd