Investigation Of Cardiovascular Calcified Plaque Grinding Mechanism And Its Application

The cardiovascular calcified plaque grinding,called atherectomy,is a minimally interventional treatment to remove calcified lesions in the artery with 1.25-2.5 mm diameter grinding wheel rotation up to 210000 rpm.The grinding force,debris,and grinding heat directly lead to complications,such as restenosis,vascular dissection,slow-flow/no-reflow and spasm et al.in atherectomy.The lack of investigation on the grinding mechanism results in high complications up to more than 80% after 30 years study and application in clinical,which seriously affect the operation process and the patient's rehabilitation after the intervention.To solve the problem caused by the grinding mechanism,the methods of experiment investigation,simulation calculation,and theory analysis are applied to study the grinding wheel motion,grinding force,debris formation,and grinding heat(include the heat created by the rotational device).Based on the clinical treatment of atherectomy,the experimental platform was established by using the clinical used device.The calcified arterial phantom was manufactured according to the mechanical properties of human tissue.Experiments were conducted on the platform to measure the trajectory of the grinding wheel.Based on the grinding wheel kinematics,the grinding force on the blood vessel wall was analyzed and the force model was constructed.The grinding force was measured by experiment to verify the force model.The grinding mechanism was analyzed by simulation and experiment by using the kinematics and force results.The debris size distribution was analyzed quantitatively.Finally,the grinding heat and heat generated by the device was studied by the experiments and theory,which identified the thermal damage condition.The method of controlling and eliminating the thermal damage in atherectomy was put forward and verified by experiments.The main conclusions and innovations are as follows:1.It is revealed that the rotational grinding wheel is rotated along the vessel and radial bounce happens to form the intermittent cutting motion.The grinding wheel motion laid a foundation to the impact force study.The grinding experiment was carried out on the platform which was designed and built by ourselves.The high-speed camera,dynamometer and environmental scanning electron microscope were used to measure the grinding wheel trajectory,grinding force and ground surface scratches.The results show that the rotational wheel takes the surrounding blood to flow.The fluid pressure generated by blood drives the grinding wheel to rotate along the vessel.The cutting and friction force,which induces the grinding wheel bounce in radial direction,occur when the grinding wheel contact with the vessel wall.The motion of grinding wheel pointed out that the both impact force and cutting force are existed in atherectomy,which have laid the foundation to the grinding force study.2.The grinding force model,consists of the grinding wheel impact force model and cutting force model based on the multi-grain smoothed particle dynamics simulation,is constructed.The method based on the probability statistics to measure the intermittent grinding force in atherectomy is proposed and applied.The larger grinding force is main reason to cause complications like dissection and spasm.The grinding force is divided into two parts: the impact force and cutting force modeled by the Hertz contact theory and the multi-grain smoothed particle dynamics(SPH)simulation.By introducing the theory of probability statistics in the process of extracting the grinding force signal,which is difficult to be determined by the changing of the grinding force direction and amplitude due to the grinding wheel motion.The error between the modeling and experiment is less than 8%.The experimental and modeling results show that more than 95% of the grinding force is derived from the impact force.Grinding force decrease is less than 10% by lowing down rotational speed.When the mass of the grinding wheel is reduced from 0.11 g to 0.043 g,the grinding force at 135000,155000,and 175000 rpm was reduced more than 90% from 1.82,2.06,and 2.31 N to 0.13,0.16,and 0.22 N,respectively.Reducing the mass of the grinding wheel can effectively reduce the grinding force,which may reduce or even eliminate the vessel dissection,spasm,and other complications.3.A debris deformation model based on the SPH and debris size model was built,which can provide a tool to solve the slow-flow/no-reflow caused by the blockage of larger debris.The debris size larger than the maximum size of the blood cells in the blood(about 30 mm)may block the micro-vessel and causing blood slow-flow/no-reflow and spasm.The single grain grinding simulation was conducted to generate the debris.The debris shape and size distribution were obtained by analyzing the debris size model which was established based on the strain failure criterion.The simulation and modeling results showed that weak connection points(connected by 1-2 SPH particles)were broken and the debris is changed from the large aspect ratio and size rod shape to small aspect ratio and size sphere shape with the increasing of grinding wheel speed.The simulation and modeling results are consistent with the experiment.The average Pearson correlation coefficient of the debris size distribution between the modeling and the experiment is higher than 0.92.When the wheel speed is higher than 23 m/s,90% of the debris size is smaller than 25 mm,which may reduce blood slow-flow/no-reflow.4.A method to separate the heating sources based on the inverse heat transfer is proposed.The grinding heat and catheter friction heat were separated in atherectomy.A heat transfer model for the flexible catheter,which generated more than 92% heat in atherectomy,is constructed to find the condition for the thermal damage.The method of pre-cooling saline and increasing the saline flow rate was put forward to controlling the catheter temperature rise,which provided a solution to the heat agglomeration and blood vessel thermal injury during the plaque grinding process.The grinding heat and catheter friction heat may cause the temperature rise of blood and vessel tissue.If the temperature rise is higher than 6?,the thermal damage occurs,which induce the blood cell agglomeration and function problem of the vessel cell.The inverse heat transfer method was used to separate the catheter friction heat and grinding heat by using the measured temperature rise of calcified plaque and built heat transfer model.The results indicated that more than 92% of the heat in the grinding process comes from the catheter friction heat.The governing equations of the whole and inside catheter were solved to obtain the temperature temporal and spatial distribution of the catheter and saline inside the catheter.The results showed that the temperature rise is higher than 6? when the slow-flow/no-reflow occurs under high rotational speed.The pre-cooling and increase the saline flow rate were proposed to compress the saline temperature,which have been validated by the experiments.This method provides a potential solution to solve the thermal damage in the plaque grinding process.