| The main factors of resistant hypertension is the excessive activation of renal sympathetic nerve.Radiofrequency ablation(RF)is a new kind of treatment method to renal sympathetic denervation.It is to ablate in the sympathetic nerve of renal artery,and sympathetic nerve irreversible necrosis occurs when the temperature is above 43?.Thus inhibiting sympathetic excitement to achieve the purpose of lowering blood pressure.Due to the renal sympathetic nerve range has uneven distribution in depth from proximal nephron to aortaventralis side,so there are different in different parts of the need to release the energy to destroy nerve fibers Therefore,in the process of surgery ablation,the ablation locations,ablation energy range,ablation duration time,and changes in hemodynamic parameters still need further research.This research mainly studies in the renal artery with the method of radiofrequency ablation in the treatment of resistant hypertension for the coupling effect of electromagnetic field,temperature field and flow field,from the angle of methodology to explore the operation effectiveness.According to the result of numerical simulation to establish ex-vivo experiment for verification,and to analyze the effects under the different treatment parameters.The concrete research content is as follows:1.RF of renal artery bifurcation vascular model is built and parameter settings.Application of COMSOL Multiphysics build 3d model with renal artery branch,radiofrequency electrode and peripheral tissue(abdomen).Based on the control equations of electromagnetic field,temperature field and flow field in the corresponding initial boundary conditions are set up.For solving electromagnetic field,select the frequency domain,and the frequency is set to 470 KHZ.Set temperature field solver and choose the transient solver.Set up to solve the total time of 60 s,and 1s as the time step to solve the current and laminar flow heat transfer.2.Multi-physics coupling simulation calculation.In the finite element calculation,set different ablation parameters combination.The RF voltage were 12 V and 15 V,ablation time for 60 s and 120 s,the blood flow velocity of 0.4 m/s and 0.7 m/s.By changing the parameters of treatment to study the influence on temperature field and the relationship with the effect of ablation,thus to verify the effectiveness of the proposed procedure.3.RF in ex-vivo experimental study.Preparation for RF frequency phantom thermal ablation experiments,simulation experiment device via equivalent principle of Reynolds number.The time-temperature data of different location can be acquired at the same time.Set ablation power for 5 W and 8 W,ablation time for 5 min and 8 min,liquid flow velocity for 0.18-0.32 m/s.By changing different experimental conditions to analyze the influence of different parameters on the temperature field and verify the correctness of simulation results and feasibility in clinical operation.Muilt-physical calculation results show that: 1.The RF electrode released energy inside the artery spread through biological tissues,the blood vessel walls and tissue outside wall had temperature rise,can achieve effective treatment temperature(i.e.,the sympathetic nerve damage temperature 43?).While the blood flow was little affected,the blood temperature rise of less than 0.5?.2.The blood flow has a certain extent cooling effect on the temperature field and reduced the heat accumulation.3.The voltage is the major influence factors.When the voltage increased from 12 V to 15 V,the highest temperature rose by about 7 ?.When the voltage and blood velocity were constant,with the increase of ablation time,the temperature field changed slowly after reaching thermal equilibrium;when the voltage and ablation time were constant,the change of velocity of the flow field had little effect on the temperature field;the maximum temperature change of not more than 1°C when the ablation time and blood flow velocity changed.The ex-vivo experimental results show that: 1.In the human body the equivalent model of the given velocity range(0.18-0.32 m/s),8 w power output,it can achieve the purpose of ablation(that is,the ?T ?6 ?),and have less effect on the blood and peripheral tissue(?T <2 ?)The safety and effectiveness of this method was verified.2.Energy output(power)is the biggest factor.When the ablation time and fluid velocity were constant,the temperature rising tendency increased significantly with the increase of output power;when the output power and fluid velocity were constant,?T increased slowly with the ablation time increased;when the output power and ablation time were constant,the higher the fluid velocity,the slower the temperature rise.Change the ablation time and fluid velocity,the change in temperature was within 0.2~2.5°C which was basically consistent with the simulation results.Based on the simulation of physical fields preliminary verified the effectiveness of RF for renal sympathetic denervation.According to the result of numerical simulation to establish ex-vivo experimental study for verification,and analyze the influence on the effect of different treatment parameters on the ablation to verify the feasibility of the operation.It provides a certain theoretical reference for clinical treatment. |
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