Numerical analysis on the effect of normotensive and hypertensive physiological conditions onto hemodynamic characteristics in stented carotid artery

An arterial re-blockage or restenosis by abnormal atherosclerosis and thrombosis progression in carotid artery is associated with the geometry of the implanted medical device, called as stent. However, the physiological conditions consisting of normotensive and hypertensive blood flow in the stented carotid artery are rarely studied in term of hemodynamic characteristic especially near the geometry of the stent strut. Thus, the objective of this study is to determine the hemodynamic effect based on its characteristics at different stent strut configurations in carotid artery as well as analyzing the critical parameters at varying blood physiological conditions. Six different geometries of stent that resembles the existing medical device have been studied at three varying physiological conditions of blood. The study was conducted through computational fluid dynamic (CFD) method to analyze the hemodynamic characteristics of the blood flow parameters. In overall physiological condition, the stent geometry of Type VI which are resembling to Acculink (Abbott Vascular), had been shown to have the best hemodynamic characteristic by the parameters of time averaged wall shear stress low (TAWSSlow), oscillatory shear index (OSI) and relative residence time (RRT), which contributed with average luminal surface area percentage about 10.443%, 99.849% and 98.736%, respectively. As the physiological condition of blood flow increased from normotensive to hypertensive, there were two parameters shown to have critical hemodynamic characteristics at different stent geometries which are TAWSSlow and time averaged wall shear stress gradient (TAWSSG) that achieved about 32.388% and 36.629%, respectively. The study had shown that the different stent strut geometries had presented different hemodynamic characteristics due to the effect by the blood flow physiological condition

Evaluation System on Haemodynamic Parameters for Stented Carotid Artery: Stent Pictorial Selection Method

Stent implantation is an alternative invasive technique for treating the narrowed artery or stenosis in carotid artery to restore blood to the brain. However, the restenosis process is usually observed after a few weeks of carotid angioplasty and stenting due to abnormal progression of atherosclerosis and thrombosis. Many studies reported that the activity of atherosclerosis and thrombosis is majorly influenced by the geometrical strut configuration. Thus, this study was carried out to determine the haemodynamic performance on different geometrical stent strut configurations based on numerical modelling and statistical analyses. Six different stent strut configurations were 3-D modelled and simulated in different physiological conditions; normal blood pressure (NBP), pre-hypertension (PH) and hypertension stage one (HS1) through computational fluid dynamic (CFD) method. The haemodynamic performance of stent was analysed based on parameters namely time averaged wall shear stress (TAWSS), time averaged wall shear stress gradient (TAWSSG), oscillatory shear index (OSI), relative residence time (RRT) and flow separation parameter (FSP). Meanwhile, Pictorial Selection Method was used to evaluate the best haemodynamic stent performance based on a scoring system. From observation, stent Type II was seen to show the highest score for TAWSS, which was 3.44 regardless of any physiological conditions. For TAWSSG, the lowest score was observed for Type V stent with 0.36. Furthermore, Type VI stent displayed the highest score for OSI while Type IV has the lowest score for FSP with 3.09 and 1.23, respectively. On the other hand, RRT was seen varying according to the physiological condition where the highest score in NBP condition was achieved by Type I while PH and HS1 condition was achieved by Type VI. In conclusion, Type VI has the best stent performance, whereas Type IV has the worst stent performance regarding the scoring system based on haemodynamic parameters. Further, Type I, Type II, Type III and Type V stents showed moderate hemodynamic performances for all physiological conditions

Flow behaviour in normal and Meniere's disease of endolymphatic fluid inside the inner ear

Meniere's disease is a rare disorder that affects the inner ear which might be more severe if not treated. This is due to fluctuating pressure of the fluid in the endolymphatic sac and dysfunction of cochlea which causing the stretching of vestibular membrane. However, the pattern of the flow recirculation in endolymphatic region is still not fully understood. Thus, this study aims to investigate the correlation between the increasing volume of endolymphatic fluid and flow characteristics such as velocity, pressure and wall shear stress. Three dimensional model of simplified endolymphatic region is modeled using computer aided design (CAD) software and simulated using computational fluid dynamic (CFD) software. There are three different models are investigated; normal (N) model, Meniere's disease model with less severity (M1) and Meniere's disease model with high severity (M2). From the observed, the pressure drop between inlet and outlet of inner ear becomes decreases as the outlet pressure along with endolymphatic volume increases. However, constant flow rate imposed at the inlet of endolymphatic showing the lowest velocity. Flow recirculation near to endolymphatic region is occurred as the volume in endolympathic increases. Overall, high velocity is monitored near to cochlear duct, ductus reuniens and endolymphatic duct. Hence, these areas show high distributions of wall shear stress (WSS) that indicating a high probability of endolymphatic wall membrane dilation. Thus, more severe conditions of Meniere's disease, more complex of flow characteristic is occurred. This phenomenon presenting high probability of rupture is predicted at the certain area in the anatomy of vestibular system

Computational analysis on stent geometries in carotid artery

Stent implantation is an altemative invasive technique for treating the narrowed artery or stenosis in carotid artery to restore blood to the brain. However, the restenosis process is usually observed after a few weeks of carotid stenting due to abnormal progression of atherosclerosis and thrombosis. Many studies reported that the activity of atherosclerosis and thrombosis is majorly influenced by the geometrical strut configuration. Thus, this study was canied out to determine the haemodynamic performance on different geometrical stent strut configurations based on numerical modelling and statistical analyses. Six different stent strut configurations were 3-D modelled and simulated in different physiological conditions; normal blood pressure (NBP), pre-hypertension (PH) and hypertension stage one (HS1) through computational fluid dynamic (CFD) method. The haemodynamic performance of stent was analysed based on parameters namely time averaged wall shear stress (TAWSS), time averaged wall shear stress gradient (TAWSSG), oscillatory shear index (OSI), relative residence time (RRT) and flow separation parameter (FSP). Meanwhile, Pictorial Selection Method was used to evaluate the best haemodynamic stent performance based on a scoring system. From observation, stent Type VI was seen to show the highest score for TAWSS, which was 2.98 in overall physiological condition. For TAWSSG, the lowest score was observed for Type V stent with 0.51. Furthermore, Type VI stent displayed the highest score for OSI while Type IV has the lowest score for FSP with 2.08 and 0.28, respectively. On the other hand, RRT was seen varying according to the physiological condition where the highest score in NBP and PH conditions were achieved by Type I while HS1 condition was achieved by Type V. In conclusion, Type VI has the best stent performance, whereas Type IV has the worst stent performance according to the scoring system based on haemodynamic parameters. Further, Type I, Type II, Type III and Type V stents showed moderate hemodynamic performances for all physiological conditions

Comparative analysis on flow over cylinder between commercial code and open source algorithm

The understanding of flow over cylinder is crucial especially in aerodynamic study.The present of vortices due to flow separation at the stagnation point of cylinder is differ with the changes of Reynolds number. This study aims to investigate the flow characteristics over cylinder with different Reynolds numbers. Computational modelling is used in predicting the flow characteristic of flow over cylinder. Two different software has been used: Code::Blocks as compiler and commercial code as a basis of comparison. Three different Reynolds number imposed in this study are 20,40 and 100 to compare the accuracy and speed of convergence. Validation has been made with the previous finding to benchmark the accuracy of the result. The parameters used in this study are velocity in x and y direction, Mach numbers, drag coefficient and pressure coefficient.A brief comparison between sequential and optimized configuration which includes multiple processors is also considered. Results show that the drag coefficient and pressure are highly dependent on Reynolds numbers. The commercial code is acknowledged to be providing better results than the applied source code. However, for the optimization issue in the future, the advancement of applied source code will obtain the similar result as compared to commercial code