Simulation of stress in a blood vessel due to plaque sediments in coronary artery disease.

Atherosclerosis is a cardiovascular disease mainly caused by plaque deposition in blood vessels. Plaque comprises components such as thrombosis, fibrin, collagen, and lipid core. It plays an essential role in inducing rupture in a blood vessel. Generally, Plaque could be described as three kinds of elastic models: cellular Plaque, hypocellular Plaque, and calcified Plaque. The present study aimed to investigate the behavior of atherosclerotic plaque rupture according to different lipid cores using Fluid-Structure Interaction (FSI). The blood vessel was also varied with different thicknesses (0.05, 0.25, and 0.5 mm). In this study, FSI simulation with a cellular plaque model with various thicknesses was investigated to obtain information on plaque rupture. Results revealed that the blood vessel with Plaque having a lipid core represents higher stresses than those without a lipid core. Blood vessels' thin thickness, like a thin cap, results in more considerable than Von Mises stress. The result also suggests that even at low fracture stress, the risk of rupture due to platelet decomposition at the gap was more significant for cellular plaques.

Investigation of the effects of miniscrew-assisted rapid palatal expansion on airflow in the upper airway of an adult patient with obstructive sleep apnea syndrome using computational fluid-structure interaction analysis.

OBJECTIVE: The objective of this study was to investigate the effects of miniscrew-assisted rapid palatal expansion (MARPE) on changes in airflow in the upper airway (UA) of an adult patient with obstructive sleep apnea syndrome (OSAS) using computational fluid-structure interaction analysis. METHODS: Three-dimensional UA models fabricated from cone beam computed tomography images obtained before (T0) and after (T1) MARPE in an adult patient with OSAS were used for computational fluid dynamics with fluid-structure interaction analysis. Seven and nine cross-sectional planes (interplane distance of 10 mm) in the nasal cavity (NC) and pharynx, respectively, were set along UA. Changes in the cross-sectional area and changes in airflow velocity and pressure, node displacement, and total resistance at maximum inspiration (MI), rest, and maximum expiration (ME) were investigated at each plane after MARPE. RESULTS: The cross-sectional areas at most planes in NC and the upper half of the pharynx were significantly increased at T1. Moreover, airflow velocity decreased in the anterior NC at MI and ME and in the nasopharynx and oropharynx at MI. The decrease in velocity was greater in NC than in the pharynx. The airflow pressure in the anterior NC and entire pharynx exhibited a decrease at T1. The amount of node displacement in NC and the pharynx was insignificant at both T0 and T1. Absolute values for the total resistance at MI, rest, and ME were lower at T1 than at T0. CONCLUSIONS: MARPE improves airflow and decreases resistance in UA; therefore, it may be an effective treatment modality for adult patients with moderate OSAS.

Analysis of Urine Flow in Three Different Ureter Models.

The ureter provides a way for urine to flow from the kidney to the bladder. Peristalsis in the ureter partially forces the urine flow, along with hydrostatic pressure. Ureteral diseases and a double J stent, which is commonly inserted in a ureteral stenosis or occlusion, disturb normal peristalsis. Ineffective or no peristalsis could make the contour of the ureter a tube, a funnel, or a combination of the two. In this study, we investigated urine flow in the abnormal situation. We made three different, curved tubular, funnel-shaped, and undulated ureter models that were based on human anatomy. A numerical analysis of the urine flow rate and pattern in the ureter was performed for a combination of the three different ureters, with and without a ureteral stenosis and with four different types of double J stents. The three ureters showed a difference in urine flow rate and pattern. Luminal flow rate was affected by ureter shape. The side holes of a double J stent played a different role in detour, which depended on ureter geometry.

Numerical analysis of urine flow through the side holes of a double J stent in a ureteral stenosis.

Ureteral stenosis presents with a narrowing in the ureter, due to an intrinsic or extrinsic ureteral disease, such as ureter cancer or retroperitoneal fibrosis. The placement of a double J stent in the upper urinary system is one of the most common treatments of ureteral stenosis, along with the insertion of a percutaneous nephrostomy tube into the renal pelvis. The effect that the side holes in a double J stent have on urine flow has been evaluated in a few studies using straight ureter models. In this study, urine flow through a double J stent's side holes was analyzed in curved ureter models, which were based on human anatomy. In ureteral stenosis, especially in severe ureteral stenosis, a stent with side holes had a positive effect on the luminal and total flow rates, compared with the rates for a stent without side holes. The more side holes a stent has, the greater the luminal and total flow rates. However, the angular positions of the side holes did not affect flow rate. In conclusion, the side holes in a double J stent had a positive effect on ureteral stenosis, and the effect became greater as the ureteral stenosis became more severe.

Change in the Upper Airway of Patients With Obstructive Sleep Apnea Syndrome Using Computational Fluid Dynamics Analysis: Conventional Maxillomandibular Advancement Versus Modified Maxillomandibular Advancement With Anterior Segmental Setback Osteotomy.

OBJECTIVE: The aim of the study was to compare the effect of conventional maxillomandibular advancement (MMA) and modified MMA with anterior segmental setback osteotomy (MMA-ASSO) on the airway changes in patients with obstructive sleep apnea syndrome (OSAS) using three-dimensional computational fluid dynamics (3D-CFD) analysis. METHODS: Two adult male patients with Class I malocclusion, lip protrusion, acute nasolabial angle, and OSAS were treated with conventional MMA (Case 1) and modified MMA-ASSO (Case 2). Individualized 3D airway models were fabricated using computed tomography data obtained 1 month before (T0) and at least 6 months after surgery (T1). A total of 7 cross-sectional areas of the airway were established, starting just above the hard palate (plane 1) with interval of 1 mm caudally. Airflow velocity and negative pressure were investigated using CFD analysis, and polysomnography studies were performed at T0 and T1. RESULTS: There were improvement of apnea-hypoapnea index and the lowest O2 level (T0 versus T1; 43.2 versus 15.2, 79% versus 90% in Case 1; 61.0 versus 6, 89% versus 92% in Case 2). At plane 2 (retropalatal area) in Cases 1 and 2, there were increase in the smallest cross-sectional areas (57.9% versus 28.4%), decrease in the airflow velocity and increase in the negative pressure at the peak of expiration (49.5% versus 31.7%; 88.4% versus 54.3%), end after expiration (53.2% versus 32.2%; 83.2% versus 47.9%), and peak of inspiration (53.1% versus 29.2%; 75.3% versus 48.2%). CONCLUSION: Modified MMA-ASSO method might be an effective treatment option for OSAS patients with improvement of airway problems and esthetic facial profile.

Numerical analysis of the urine flow in a stented ureter with no peristalsis.

A ureteral stenosis or occlusion causes the disturbance of normal urine flow and results in renal failure. Ureteral stents are used to relieve the stagnation of urine in the upper urinary tract. Peristalsis in the ureter, which occurs to help urine flow, becomes to weaken when a stent is inserted and effective peristalsis disappears as time goes on, and a stented ureter seems to be tubular and curved in the human body. Double J stents, which are manufactured by many medical companies and are used widely these days, have different geometries of side holes in the stent shafts. In total, 12 models-six curved models of a stented ureter according to different numbers and positions of side holes and ureteral and stent stenoses and another six straight models for comparison with the curved ones-were made based on the data collected from 19 men. The flow rate and pattern in the stented ureter were evaluated using computational fluid dynamics (CFD). According to the results, curved models reflecting the human anatomy seem to be more desirable in the CFD simulation of urine flow and must be good for evaluating the effect of geometrical variations in stent design on urine flow.

Numerical analysis of the effect of side holes of a double J stent on flow rate and pattern.

A double J stent has been used widely these days for patients with a ureteral stenosis or with renal stones and lithotripsy. The stent has multiple side holes in the shaft, which supply detours for urine flow. Even though medical companies produce various forms of double J stents that have different numbers and positions of side holes in the stent, the function of side holes in fluid dynamics has not been studied well. Here, the flow rate and pattern around the side holes of a double J stent were evaluated in curved models of a stented ureter based on the human anatomy and straight models for comparison. The total flow rate was higher in the stent with a greater number of side holes. The inflow and outflow to the stent through the side holes in the curved ureter was more active than in the straight ureter, which means the flow through side holes exists even in the ureter without ureteral stenosis or occlusion and even in the straight ureter. When the diameter of the ureter changed, the in-stent flow rate in the ureter did not change and the extraluminal flow rate was higher in the ureter with a greater diameter.

Influences of Geometric Configurations of Bypass Grafts on Hemodynamics in End-to-Side Anastomosis.

BACKGROUND: Although considerable efforts have been made to improve the graft patency in coronary artery bypass surgery, the role of biomechanical factors remains underrecognized. The aim of this study is to investigate the influences of geometric configurations of the bypass graft on hemodynamic characteristics in relation to anastomosis. MATERIALS AND METHODS: The Numerical analysis focuses on understanding the flow patterns for different values of inlet and distal diameters and graft angles. The Blood flow field is treated as a two-dimensional incompressible laminar flow. A finite volume method is adopted for discretization of the governing equations. The Carreau model is employed as a constitutive equation for blood. In an attempt to obtain the optimal aorto-coronary bypass conditions, the blood flow characteristics are analyzed using in vitro models of the end-to-side anastomotic angles of 45°, 60° and 90°. To find the optimal graft configurations, the mass flow rates at the outlets of the four models are compared quantitatively. RESULTS: This study finds that Model 3, whose bypass diameter is the same as the inlet diameter of the stenosed coronary artery, delivers the largest amount of blood and the least pressure drop along the arteries. CONCLUSION: Biomechanical factors are speculated to contribute to the graft patency in coronary artery bypass grafting.

Hemodynamic analysis of coronary circulation in angulated coronary stenosis following stenting.

The present study in angulated coronary stenosis used human in vivo hemodynamic parameters and computed simulation, both qualitatively and qualitatively, to evaluate the influence of flow velocity and wall shear stress (WSS) on coronary atherosclerosis, the changes of hemodynamic indices following coronary stenting, and their effect on evolving in-stent restenosis. Initial and follow-up coronary angiographies in patients with angulated coronary stenosis were performed (n=60). The optimal degree of coronary stenting for angulated coronary stenosis had two models, the less than 50% angle changed group (model 1, n=33) and the more than 50% angle changed group (model 2, n=27). This angle change was based on the percentage change of vascular angle between pre- and post-intracoronary stenting. The flow-velocity wave obtained from in vivo intracoronary Doppler study data was used for in vitro numerical simulation. Spatial and temporal patterns of the flow-velocity vector and recirculation area were drawn throughout the selected segment of coronary models. WSS of pre- and post-intracoronary stenting was calculated from three-dimensional computer simulation. As results, follow-up coronary angiogram demonstrated significant difference in the percentage of diameter stenosis between the two groups (group 1: 40.3 +/- 30.2 vs. group 2: 25.5 +/- 22.5%, p < 0.05). Negative shear area on 3D simulation, which is consistent with the re-circulation area of flow vector, was noted on the inner wall of the post-stenotic area before stenting. The negative WSS disappeared after stenting. High spatial and temporal WSS before stenting fell within the range of physiologic WSS after stenting. This finding was more prominent in model 2 (p < 0.01). The present study suggests that hemodynamic forces exerted by pulsatile coronary circulation, termed WSS, might affect the evolution of atherosclerosis within the angulated vascular curvature. Moreover, geometric characteristics, such as the angular difference between pre- and post- intracoronary stenting might define optimal rheologic properties for vascular repair after stenting.