ABSTRACT
Objective To investigates the applicability of cutting balloon in the pretreatment of superficial coronary artery calcified lesions, so as to decrease the occurrence of serious consequences in the treatment of calcified lesions. Methods The effect of cutting balloon on calcified plaques with different curvatures, thickness, and length was analyzed using the finite element method, with normal balloon as a control. The thickness of calcified plaque was set to 0.3 mm and 0.4 mm, and the length was set to 2 mm and 4 mm. The calcification degree was set to 120°, 180°, 270°and 360° according to the intravenous ultrasound (IVUS) calcification severity grading, with a total of 16 types of calcified plaques. The brittle fracture module was used to simulate calcification fracture of calcified plaques, and virtual stent implantation was carried out based on pretreatment simulation. The effect of pretreatment was evaluated by calcification fracture condition and stent roundness. Results For superficial calcification lesions, in lesions less than 120°, the balloon could not remove the calcification plaque obstruction, and the stent roundness rate was 82.75%. In 180° calcified lesions with thickness of less than 0.3 mm, the calcification was broken by cutting balloon under 1 215.9 kPa expansion pressure, and the post-stent roundness rate was 74.42%; normal balloon could not cause calcification fracture under safe expansion pressure (1 418.55 kPa). In 270°calcified lesions with thickness less than 0.3 mm, the normal balloon produced 3 fractures under 1 013.25 kPa expansion pressure. The cutting balloon produced 2 fractures under 1 013.25 kPa expansion pressure, and the balloon could not fracture the circular calcified lesions with thickness of 0.3 mm. Conclusions Cutting balloon is recommended for 180°calcified lesions with thickness less than 0.3 mm, the normal balloon is recommended for 270°calcified lesions, and balloon pretreatment is not recommended for annular lesions with thickness greater than 0.3 mm.
ABSTRACT
Thrombosis is the process of platelet adhesion and aggregation or blood coagulation after the body is subjected to certain physical and chemical stimuli. At present, the use of basic experimental research and computational simulation to understand thrombosis has become a research hotspot. The complex process of thrombosis makes computational modeling very difficult, but the development of calculation models has still made great progress. At present, a variety of calculation models for thrombosis have been developed, including coagulation models based on ordinary differential equations, mathematical models based on finite element analysis, Lattice-Boltzmann method models, smooth particle dynamics method models, etc. Each model has its advantages and disadvantages.In this review, the physiological mechanism of thrombosis was explained, the models for simulating thrombosis were also systematically sorted out and evaluated, and the limitations of computational simulation and future application prospects were summarized as well.
ABSTRACT
BACKGROUND: Axial-flow blood pump is a main pump for ventricle assistance. Previous researches demonstrate that poor hemocompatibility of blood pump is an important factor for hemolysis and thrombus.OBJ ECTTVE: To design an axial-flow blood pump based on previous kinds of blood pumps through changing whole appearance and impeller shape of the pump by using Computer-Aided Design CAD) and Computational Fluid Dynamics (CFD), and manufacture it successfully.DESIGN: Rationality of theoretical design was verified by practical tests.SETTTNG: Beijing Anzhen Hospital of Capital University of Medical Sciences Department of Biomedical Engineering,Beijing Institute of Heart, lung and Blood Vessel Diseases; the Faurteenth Institute of China-Aerospace Science and Industry Corporation.MATERIALS: Body of blood pump and impeller were titanium alligation, and shaft bearing was ceramic. Test in vitro was accorded to artificial ventricular assist device which was provided by Department of Biomedical Engineering, Beijing Anzhen Hospital of Capital University of Medical Sciences. Experimental goats were provided by Experimental Animal Center, Beijing Anzhen Hospital of Capital University of Medical Sciences.METHODS: Since the beginning of 2005, a model of axial flow blood pump was designed in the 14th Institute of China-Aerospace Science and Industry Corporation base on decreasing shearing force and circulating dead bands. In the process, CAD and CFD were used to generate the geometrical data document of pump's structure, which included the figures of pump's body, shape and number of impeller's vanes, the structure and position of the guide vanes, and the size of impeller's screw-pitch. And then, NC machine tool was used for shaping. Finally, axial-flow blood pump was fixed on artificial ventricular assist device which was provided by Department of Biomedical Engineering, Beijing Anzhen Hospital of Capital University of Medical Sciences. The pump's hemodynamic output was 5 L/min and the average pressure was 13.3 kPa under the mixture of glycerin and water and fresh anticoagulation goat blood. The samples were collected at every one half hour during pumps being pumping for 4 hours. According to testing pressure output of blood pump, normalized index of hemolysis (NIH) was used to reflect content of free hemoglobin in plasma, observe thrombogenesis in pump and verify pump's hemodynamic output and vascular damaging degree.RESULTS: Shaped axial-flow blood pump included body, impeller, guide vanes, ceramic shaft bearing, export and import. The volume was 63 mL. Experimental results in vitro indicated that when the rotation speed of blood pump was 10 000 r/min, its pressure and flow output were 21.01 kPa and 6.0 L/min. The hemodynamic output might satisfy for left ventricular assistance. Surface temperature did not change obviously during successive rotation. The calculation indicated that most parts in blood pump showed a streaming flow. The mean NIH was (0.047±0.017) g/100 L, which was less than that of previous pumps; while, thrombogenesis was not observed in blood pump.CONCLUSTON: Axial-flow blood pump designed by using CAD and CFD can not only satisfy for the hemodynamics of a left ventricular assistant devices, but also the blood damage is milder than previous pumps. Therefore, axial-flow blood pump improves blood compatibility.
ABSTRACT
Hemolysis caused by blood pumps is a very important characteristic. In vitro hemolysis test circuits were constructed to operate the model I centrifugal pump, the model II axial flow pump, the magnetic coupling pump and the model I & II spiral mixed pump. The output of all pumps was set at flow 5 L/min, an average pressure of 100 mmHg. Experiments were conducted for 4 hours at room temperature(25 degrees C) with 500 ml fresh anticoagulant sheep blood. Blood samples were taken for plasma free-hemoglobin measurement, and the change in temperature at the pump outlet port was measured during the experiment. Calculate the normalized index of hemolysis (NIH). The results showed that there was no relationship either between the pump rotational speed and the NIH in five types of blood pumps, or between change in temperature at the pump outlet port and NIH. The dynamic fluid field caused by pump design and structure could be the main cause of blood damage.