Shape Of Stenoses Research Articles

Heat and mass diffusion to williamson fluid streaming through a tube with multiple stenoses while subjected to periodic body acceleration

This article examines a mathematical framework that describes the versatile behavior of heat and mass exchange in blood flowing through a narrowed vessel having multiple stenoses. The geometry of a channel having multiple stenoses with an asymmetrical axial axis and a symmetrical radial axis can be visualized by applying a suitable mathematical expression. The geometry of the chosen model considers the height and shape of stenoses. The modification in shape parameter is used to capture variations in the shape of the stenoses in the artery. The blood is supposed to be isochoric (incompressible), while its rheological behavior is characterized by Williamson’s fluid model. The transfer of momentum is analyzed using the equation of motion in cooperation with the continuity equation. In addition, the equations of heat conduction and diffusion are utilized, respectively, to illustrate the distributions of heat and mass. Simplified forms of momentum, mass, and heat transport equations are achieved by incorporating dimensionless quantities and moderate stenosis conditions. A well-known explicit finite difference approach is utilized to solve the emergent non-linear system of governing equations numerically. The influence of different evolving parameters on the flow field along with mass and heat distributions is illustrated through various plots.

Localization and shape of stenoses in central lung carcinoma - Sensitivity and precision of MDCT VB and FB.

SummaryThe objective is to present diagnostic capabilities of virtual bronchoscopy (VB) and fiberoptic bronchoscopy (FB) for determining the localization and shape of stenoses in patients with central lung carcinoma. A systematic study was performed on 220 patients aged 11-83 (54.36±17.24) years with endobronchial disease using the FB and VB methods during the 2013-2017 period. Central carcinoma of the lung was found on VB in 130 patients and on FB in 120 patients. Other nosologic diseases were found in 22 patients. Right localization of central carcinoma prevailed over left localization in both sexes. A significant difference in the localization criterion was found in female patients examined by VB (U-test, p=0.01). VB and FB yielded 86.5% vs. 91.60% precision and 85% vs. 94.5% sensitivity. In conclusion, VB was found to be a successful noninvasive method for determining the localization of lung tumors and shape of stenoses, which are essential in the diagnosis of malignant processes.

Validation of pressure drop assessment using 4D flow MRI-based turbulence production in various shapes of aortic stenoses.

To validate pressure drop measurements using 4D flow MRI-based turbulence production in various shapes of stenotic stenoses. In vitro flow phantoms with seven different 3D-printed aortic valve geometries were constructed and scanned with 4D flow MRI with six-directional flow encoding (ICOSA6). The pressure drop through the valve was non-invasively predicted based on the simplified Bernoulli, the extended Bernoulli, the turbulence production, and the shear-scaling methods. Linear regression and agreement of the predictions with invasively measured pressure drop were analyzed. All pressure drop predictions using 4D Flow MRI were linearly correlated to the true pressure drop but resulted in different regression slopes. The regression slope and 95% limits of agreement for the simplified Bernoulli method were 1.35 and 11.99 ± 21.72 mm Hg. The regression slope and 95% limits of agreement for the extended Bernoulli method were 1.02 and 0.74 ± 8.48 mm Hg. The regression slope and 95% limits of agreement for the turbulence production method were 0.89 and 0.96 ± 8.01 mm Hg. The shear-scaling method presented good correlation with an invasively measured pressure drop, but the regression slope varied between 0.36 and 1.00 depending on the shear-scaling coefficient. The pressure drop assessment based on the turbulence production method agrees well with the extended Bernoulli method and invasively measured pressure drop in various shapes of the aortic valve. Turbulence-based pressure drop estimation can, as a complement to the conventional Bernoulli method, play a role in the assessment of valve diseases.

A numerical study on the effect of trapezium stenosis shape on the axisymmetric flow field around stenosis

Numerical simulations on the pulsatile flow in stenosed tubes were conducted to investigate the effect of trapezium shape of stenosis on the flow field around stenoses. Four trapezium shapes of stenoses were considered by varying contraction, plateau, and expansion parts of stenoses for different stenosis area reduction ratios. The Galerkin finite element method based on the P2P1 mixed element was employed to solve the axisymmetric incompressible Navier-Stokes equations and the continuity equation. The proposed numerical method was validated by solving a benchmark problem of stenotic flow. It was found that the average pressure profile along the centerline was more affected by the contraction shape than the expansion shape. It was also revealed that the average wall shear stress of mild contraction was greater than that of sudden contraction around the stenotic region. Furthermore, the pressure drop across the stenosis was found to be associated with the form drag experienced by the stenosis.

Pulsatile flow of viscous and viscoelastic fluids in constricted tubes

The unsteady flow of blood through stenosed artery, driven by an oscillatory pressure gradient, is studied. An appropriate shape of the time-dependent stenoses which are overlapped in the realm of the formation of arterial narrowing is constructed mathematically. A msathematical model is developed by treating blood as a non-Newtonian fluid characterized by the Oldroyd-B and Cross models. A numerical scheme has been used to solve the unsteady nonlinear Navier-stokes equations in cylindrical coordinate system governing flow, assuming axial symmetry under laminar flow condition so that the problem effectively becomes two-dimensional. Finite difference technique was used to investigate the effects of parameters such as pulsatility, non-Newtonian properties and the flow time on the velocity components, the rate of flow, and the wall shear stress through their graphical representations quantitatively at the end of the paper in order to validate the applicability of the present improved mathematical model under consideration.

Quantitative contrast‐enhanced myocardial perfusion magnetic resonance imaging: Simulation of bolus dispersion in constricted vessels

Quantification of myocardial blood flow (MBF) by means of T1-weighted first-pass magnetic resonance imaging (MRI) requires knowledge of the arterial input function (AIF), which is usually estimated from the left ventricle (LV). Dispersion of the contrast agent bolus may occur between the LV and the tissue of interest, which leads to systematic underestimation of the MBF. The aim of this study was to simulate the dispersion along a simplified coronary artery with different stenoses. To analyze the dispersion in vessels with typical dimensions of coronary arteries, simulations were performed using the computational fluid dynamics approach. Simulations were accomplished on straight vessels with integrated stenoses of different degrees of area reduction and length as well as two different shapes-an axial symmetric and an asymmetric. Two boundary conditions were used representing myocardial blood flow at rest and under hyperemic conditions. The results under steady boundary conditions show that the dispersion is more pronounced in resting condition than during hyperemia yielding an underestimation of the MBF around 15% in the resting state and around 8% under stress conditions. At the outlet of the vessel an axial symmetric stenosis results in increased dispersion whereas an asymmetric stenosis yields a reduction. Due to the more severe dispersion, resting MBF may be more underestimated in quantitative myocardial perfusion MRI studies compared with MBF under stress conditions. In consequence the myocardial perfusion reserve may be overestimated. The amount of systematic error depends in a complex way on the shape and degree of stenoses.

Blood Flow Through an Artery with Mild Stenosis: A Two-layered Model, Different Shapes of Stenoses and Slip Velocity at the Wall

Blood Flow Through an Artery with Mild Stenosis: A Two-layered Model, Different Shapes of Stenoses and Slip Velocity at the Wall

Hemodynamic consequences of stenosis remodeling during coronary angioplasty.

Quantitative hemodynamic assessment during various endovascular interventions including balloon angioplasty is lacking. Translesional pressure drops measured by angioplasty catheters can cause flow blockage and thus lead to inaccurate estimates of preintervention and postintervention flow rates. A new analytical model of the flow rate-pressure drop relation across vascular stenoses is utilized that is nonlinear yet relatively simple in principle, easily applicable in vivo, and compatible with the presence of catheters. The model incorporates in vitro experimental evidence, angiographic data on the dimensions and shapes of coronary arterial stenoses before and after balloon angioplasty, reported translesional pressure gradients, and measurements of coronary flow reserve. Reasonable estimates of mean coronary artery flow rates and translesional pressure drops in the absence of angioplasty catheters are obtained. Prior to angioplasty significant flow restriction across a 68% diameter stenosis exists during hyperemic flow conditions. Following successful balloon dilation, increased minimal cross-sectional area (residual 40% diameter stenosis) results in an improved flow rate-pressure drop relation. Despite minimal flow restriction during hyperemic conditions following angioplasty remodeling, residual luminal constriction leads to elevated wall shear stress levels within the entry region of the stenosis. The flow analysis described may be of clinical utility in evaluating the hemodynamic significance of the anatomic severity of stenoses in coronary and peripheral arteries before and after endovascular therapeutic interventions.

734-6 ANGUS: A New Approach to Three-dimensional Reconstruction of Geometry and Orientation of Coronary Lumen and Plaque by Combined Use of Coronary Angiography and IVUS

Three-dimensional (3-D) vessel reconstruction using intravascular ultrasound (IVUS) is limited by the lack of information on the real vessel curvatures and the orientation of the IVUS catheter. To overcome these limitations a method was developed using data obtained from ANGiography and intravascular UltraSound (ANGUS). This technique provides real spatial geometry and orientation of coronary lumen and plaque. The artery is studied by IVUS during a pull-back (PB) of the IVUS catheter at a speed of 1 mm/s. Start and end of the PB are recorded by biplane fluoroscopy (BF) and finally biplane coronary angiography (BA) is performed without changes in geometrical X-ray settings. Using a new computer program the contours of the lumen-plaque and plaque-adventitia boundaries are semi-automatically detected at 0.5 mm intervals. BF allows geometrical reconstruction of the catheter trajectory, which is the path of the IVUS transducer during PB. Combined use of the IVUS data, the catheter trajectory and the lumen contours in the BA provides a unique 3-D reconstruction of coronary arteries without any evidence of an additional unknown geometric factor. Studying the trajectory in a vessel phantom of known dimensions a high accuracy was found (distance between reconstructed and real trajectory at any point < 2 mm). First application in a human right coronary artery in-vivo (length: 75 mm) showed a difference of 2% between the length of the reconstructed trajectory and the PB distance. Checking the locations of the origin of side-branches in the 3-D reconstruction and BA differences of less than 2 mm were found. Location and shape of stenoses in simulated projections of the reconstructed lumen matched well with BA. However, at the site of a previous PTCA luminal haziness in angiography and dissection observed by IVUS may slightly reduce the accuracy of this technique. Thus combining ANGiography and intravascular UltraSound (ANGUS) is promising and provides a unique reconstruction of 3-D coronary geometry.

Improved stenosis geometry by quantitative coronary arteriography after vigorous risk factor modification

This study is a randomized, controlled, blinded, arteriographic trial to determine the effects of a low-cholesterol, low-fat, vegetarian diet, stress management and moderate aerobic exercise on geometric dimensions, shape and fluid dynamic characteristics of coronary artery stenoses in humans. Complex changes of different primary stenosis dimensions in opposite directions or to different degrees cause stenosis shape change with profound effects on fluid dynamic severity, not accounted for by simple percent narrowing. Accordingly, all stenosis dimensions were analyzed, including proximal, minimal, distal diameter, integrated length, exit angles and exit effects, determining stenosis shape and a single integrated measure of stenosis severity, stenosis flow reserve reflecting functional severity. In the control group, complex shape change and a stenosis —molding characteristic of statistically significant progressing severity occurred with worsening of stenosis flow reserve. In the treated group, complex shape change and stenosis molding characteristic of significant regressing severity was observed with improved stenosis flow reserve, thereby documenting the multidimensional characteristics of regressing coronary artery disease in humans.

Pathophysiologie der Stenosen von Kehlkopf und Trachea

Behind the relatively uniform symptomatics of the many shapes of stenoses of larynx and trachea, there is hiding a multitude of factors and problems pathophysiologically important and worth of consideration which possibly could not thoroughly be treated within the asserted frame. With regard to the special pathophysiology such diseases or causes of diseases were accentuated which, so far, were less known in general, i. e. those concerning in particular the early childhood or those tending towards the boundaries of neighbouring disciplines. Other stenosis-creating diseases such as the benign and malign new formations and a number of traumatic stenoses were kept in the background as neither any vital new aspects were found in spite of the multitude of publications in world literature with regard to this special subject nor any particular form of illness lately was subject to detailed discussions.

Pathophysiology of stenoses of larynx and trachea

Behind the relatively uniform symptomatics of the many shapes of stenoses of larynx and trachea, there is hiding a multitude of factors and problems pathophysiologically important and worth of consideration which possibly could not thoroughly be treated within the asserted frame. With regard to the special pathophysiology such diseases or causes of diseases were accentuated which, so far, were less known in general, i. e. those concerning in particular the early childhood or those tending towards the boundaries of neighbouring disciplines. Other stenosis-creating diseases such as the benign and malign new formations and a number of traumatic stenoses were kept in the background as neither any vital new aspects were found in spite of the multitude of publications in world literature with regard to this special subject nor any particular form of illness lately was subject to detailed discussions.