Simulation study of thermal injury to the saphenous nerve based on temperature in radiofrequency ablation for the treatment of varicose veins
Objective Radiofrequency ablation(RFA)for the treatment of varicose veins(VVs)is a procedure in which radiofrequency energy is released into the vein lumen,damaging the endothelium of the vein with a thermal effect and closing the blood vessel to achieve the therapeutic goal.However,because the saphenous nerve is closely associated with or even entangled with the veins of the lower limbs,saphenous nerve injury is the most common complication of this procedure.Therefore,this paper intends to study the nerve damage by combining finite element calculations and neurophysiological modeling of RFA for VVs.Methods Three-dimensional models of veins and nerves at three different relative positions were established by using COMSOL multiphysics field software.The temperature distribution around the tissues and the thermal damage of the nerves were calculated by using the coupled electric-thermal-fluid finite element method.A Hodgkin-Huxley based neurophysiological model was developed with MATLAB software to further validate the effect of elevated temperature on nerves from the perspective of neuronal response frequency.Results The temperature of the tissue surrounding the blood vessels decreased progressively with distance from the electrodes.The maximum nerve temperatures in the positional relationships of vascular-nerve companion and vascular-nerve intertwining were up to 54.7℃and 62℃,respectively.For cases where the vein was located between two nerve trunks,the temperature was higher at the bifurcation of the nerve and could reach 65.5℃.The temperature distribution increased with the proximity to blood vessels.Above 45℃the nerve tissue began to show damage,and the area of damage as well as the fraction of damage increased with time.Nerves exhibited different properties when stimulated to generate action potentials at different temperatures.Between 37℃and 48℃,the frequency of neuronal action potential vibration increased and the amplitude decreased slightly with increasing temperature.Neuronal action potential vibrational frequency tended to zero at temperatures above 48℃.Conclusions The distribution of nerve locations influences the decision to treat VVs by RFA.The heat from the RFA process can cause irreversible nerve damage,and 48℃is the temperature threshold for nerve damage during the treatment of varicose veins.
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