Study On Flow Field Of Renal Denervation Based On Numerical Simulation And PIV Experiments

Hypertension is one of the health problems that cause worldwide concern,among which the complications caused by resistant hypertension（RH）do great harm to the health of patients.Renal denervation（RDN）has become an effective method for the treatment of RH.Its principle is that the radiofrequency（RF）ablation electrode is inserted into the inner wall of the renal artery to release energy.So that the sympathetic nerve around the renal artery is irreversibly necrotic,to inhibit the sympathetic nerve hyperactivity and achieve the purpose of reducing blood pressure.This process involves the coupling effect of electromagnetic field,temperature field and flow field.At present,different types of RF electrodes are used in clinical practice.However,the changes of renal artery flow field and hemodynamic parameters need to be further studied when each electrode is ablated under different ablation parameters and arterial blood flow velocities.In this study,the multi-field coupling effects of electromagnetic field,temperature field and flow field during single electrode,spiral electrode,balloon double electrodes and balloon four electrodes ablation were studied by using numerical simulation software,that is,the distribution of flow field in the renal artery during ablation and the changes of hemodynamic parameters（blood flow velocity,wall pressure,shear rate and vorticity）before and after ablation.Particle image velocimetry（PIV）is used to obtain the distribution of flow field in the renal artery during different RF electrode ablation,which verified the accuracy of numerical simulation.The specific research contents are as follows.1.Construction of the geometric model of the renal artery and RF electrodes.Based on the physiological and anatomical characteristics of the renal artery,the renal artery model was established by using a medical image 3D reconstruction tool,and the parameters were set according to the anatomical statistics.The models of single electrode,spiral electrode,balloon double electrodes and balloon four electrodes were established by Solid Works software,and the parameters were set according to the specifications of the commercial RF ablation electrode.2.Numerical simulation of multi-physical field coupling of RDN.The numerical simulation of electromagnetic field,temperature field and flow field coupling by COMSOL Multiphysics finite element software.Objective to study the changes of the flow field and hemodynamics parameters in the renal artery when single electrode,spiral electrode,balloon double electrodes and balloon four electrodes were ablated under different voltage（10 V,20 V,30 V）,ablation time（20 s,40 s,60 s）and different physiological characteristics（low blood flow velocity of 0.2 m/s,medium blood flow velocity of 0.5 m/s,high blood flow velocity of 0.8 m/s）,which will discuss the safety of four kinds of RF electrodes and give some clinical suggestions.3.PIV Experimental Study.The 3D technology was used to print the renal artery and RF electrode model,respectively.Preparation of phantom with polyvinyl alcohol and other materials to simulated renal artery tissue.The PIV experimental platform was built by the PIV system and peristaltic pump.The images of the flow field in the renal artery were obtained by PIV when RDN was performed with single electrode,spiral electrode,double electrodes and four electrodes.Then the accuracy of numerical simulation results was verified.The results of numerical simulation show that: 1.During the ablation of four kinds of RF electrodes,there was a minimum velocity of less than 0.05 m/s at the end of the electrode or balloon,but no vortex phenomenon was formed in the velocity minima of single electrode,spiral electrode and balloon double electrodes.Although the balloon four electrodes formed the eddy current phenomenon,the condition of thrombus formation was not reached by the evaluation of hemodynamic parameters such as shear rate.2.With the increase of ablation voltage（10-30 V）,the hemodynamic parameters of single electrode,spiral electrode,balloon double electrodes and balloon four electrodes maximum increased by 1.69%（vorticity）,2.62%（mean wall pressure）,4.99%（shear rate）and 5.51%（shear rate）,respectively.With the increase of ablation time（20-60 s）,the hemodynamic parameters of single electrode,spiral electrode,balloon double electrodes and balloon four electrodes maximum increased by 0.23%（vorticity）,0.32%（mean wall pressure）,0.49%（shear rate）and 0.52%（shear rate）,respectively.3.In the range of blood flow velocity 0.2-0.8 m/s,the hemodynamic parameters of before and after the single electrode and spiral electrode ablation maximum increased 2.6 times and 3.4 times,respectively.At a low blood flow velocity of 0.2 m/s,the hemodynamic parameters of before and after balloon double electrodes and balloon four electrodes ablation maximum increased by 2.4 and 3.5 times,respectively.However,at a high blood flow velocity of 0.8 m/s,the shear rate and vorticity increased by 4.8 and 5.7times before and after balloon double electrode ablation,and 5.3 and 5.9 times before and after balloon four electrodes ablation.The results of the PIV experiment showed that: 1.There was no eddy current near the RF electrode and catheter during single electrode ablation.The blood in the renal artery showed spiral flow during spiral electrode ablation,and there was velocity reflux at the end of the electrode.There was no eddy current at the end of the balloon during double electrodes ablation.There was a small eddy current at the end of the balloon during balloon four electrodes ablation.2.The velocity values of the renal artery were compared with the simulation results when single electrode,spiral electrode,balloon double electrodes and balloon four electrodes were ablated.The maximum relative error was 6.4%,14.3%,13% and 15.4%,respectively.Conclusion: 1.It is not easy to form a thrombus in the renal artery when using four kinds of RF electrodes,which ensures the safety of the operation.2.With the increase of ablation parameters,the hemodynamic parameters in the flow field increased,especially the change of ablation voltage.3.When the blood flow velocity in the renal artery of clinical patients is high,it is recommended to use the single electrode or spiral electrode ablation to avoid large shear rate and vorticity.When the blood flow velocity is low,it is suggested to use balloon four electrodes or balloon double electrodes ablation,which can achieve a therapeutic effect in a short time and avoid greater damage to vascular intima.4.The flow field of the renal artery obtained by the PIV experiment is similar to that in simulation,and the maximum relative error is 15.4%compared with the velocity value in numerical simulation,which preliminarily verifies the accuracy of numerical simulation results.Based on the numerical simulation and PIV experiments,the flow field distribution and hemodynamic parameters of single electrode,spiral electrode,balloon double electrodes and balloon four electrodes were studied under different ablation parameters and blood flow velocities.The safety of four RF electrodes were evaluated from the view of flow field and clinical suggestions were given according to the changes of hemodynamic parameters before and after ablation,which provided a certain reference for clinical practice.