Influence of structural geometry on the severity of bicuspid aortic stenosis

2004 ◽  
Vol 287 (3) ◽  
pp. H1410-H1416 ◽  
Author(s):  
Kathryn E. Richards ◽  
Dimitri Deserranno ◽  
Erwan Donal ◽  
Neil L. Greenberg ◽  
James D. Thomas ◽  
...  
Keyword(s):  
Pressure Loss ◽  
Three Dimensional ◽  
Left Ventricular ◽  
Pressure Recovery ◽  
Orifice Diameter ◽  
Local Geometry ◽  
Reduced Pressure ◽  
Orifice Area ◽  
Area Functional ◽  
The Impact

Doppler-derived gradients may overestimate total pressure loss in degenerative and prosthetic aortic valve stenosis (AS) due to unaccounted pressure recovery distal to the orifice. However, in congenitally bicuspid valves, jet eccentricity may result in a higher anatomic-to-effective orifice contraction ratio, resulting in an increased pressure loss at the valve and a reduced pressure recovery distal to the orifice leading to greater functional severity. The objective of our study was to determine the impact of local geometry on the total versus Doppler-derived pressure loss and therefore the assessed severity of the stenosis in bicuspid valves. On the basis of clinically obtained measurements, two- and three-dimensional computer simulations were created with various local geometries by altering the diameters of the left ventricular outflow tract (LVOT; 1.8–3.0 cm), orifice diameter (OD; 0.8–1.6 cm), and aortic root diameter (AR; 3.0–5.4 cm). Jet eccentricity was altered in the models from 0 to 25°. Simulations were performed under steady-flow conditions. Axisymmetric simulations indicate that the overall differences in pressure recovery were minor for variations in LVOT diameter (<3%). However, both OD and AR had a significant impact on pressure recovery (6–20%), with greatest recovery being the larger OD and the smaller recovery being the AR. In addition, three-dimensional data illustrate a greater pressure loss for eccentric jets with the same orifice area, thus increasing functional severity. In conclusion, jet eccentricity results in greater pressure loss in bicuspid valve AS due to reduced effective orifice area. Functional severity may also be enhanced by larger aortic roots, commonly occurring in these patients, leading to reduced pressure recovery. Thus, for the same anatomic orifice area, functional severity is greater in bicuspid than in degenerative tricuspid AS.

scholarly journals Optimization Study of the Dump Diffuser in Gas Turbine to Reduce Pressure Loss

2018 ◽  
Vol 2018 ◽  
pp. 1-14
Author(s):  
Fei Xing ◽  
Hao Su ◽  
Shining Chan ◽  
Leilei Xu ◽  
Xinyi Yu
Keyword(s):  
Pressure Loss ◽  
Total Pressure ◽  
Static Pressure ◽  
Vortex Method ◽  
Total Pressure Loss ◽  
Pressure Recovery ◽  
Test Model ◽  
Gap Ratio ◽  
Efficient Combustion ◽  
The Impact

As a key component-connecting compressor and the entrance of combustion chamber, the diffuser is able to increase the pressure and slow down the airflow in order to promote efficient combustion as well as avoid a large amount of pressure loss. In this paper, experimental investigation and numerical studies have been carried out to understand the effects of air bleeding from dump region and dump gap ratio on the total pressure loss and static pressure recovery of the dump diffusers. The ultimate objective is optimizing the dump diffuser design to get the maximum static pressure recovery and minimum total pressure loss. A simplified test model is used to study the effect of the air bleeding from the outer dump region and the dump gap ratio on the total pressure loss and static pressure recovery in the dump diffuser. The impact of the dump gap ratio in the performance of the dump diffusers has also been discussed. Nearly all the pressure raise occurs in the prediffuser, and most of the total pressure loss occurs in the dump region. For the recirculating area in the dump region, the controllable vortex can be introduced. Bleeding air from the outer dump region can improve the velocity distribution near the flame tube. The results show that when 0.4% of the air is bled from outer dump region, the performance of the dump diffuser is optimal. Hence, the controllable vortex method is effective for improving the performance of the dump diffuser.

Characterization and Optimization of a Three-Dimensional T-Type Micromixer for Convective Mixing Enhancement With Reduced Pressure Loss

2010 ◽  
Author(s):  
Cesar A. Cortes-Quiroz ◽  
Alireza Azarbadegan ◽  
Mehrdad Zangeneh
Keyword(s):  
Performance Optimization ◽  
Pressure Loss ◽  
Three Dimensional ◽  
Performance Criteria ◽  
Mixing Enhancement ◽  
Optimization Strategy ◽  
Reduced Pressure ◽  
Design And Optimization ◽  
Two Fluids ◽  
Convective Mixing

Numerical simulations and experiments are used to evaluate the flow and mixing characteristics of a proposed convective 3-D T-type micromixer. The study presents a parametric study and performance optimization of this micromixer based on the variation of its geometry. To investigate the effect of design and operation parameters on the device performance, a systematic design and optimization methodology is applied; it combines Computational Fluid Dynamics (CFD) with an optimization strategy that integrates Design of Experiments (DOE), Surrogate modeling (SM) and Multi-Objective Genetic Algorithm (MOGA) techniques. The degree of mixing and the pressure loss in the mixing channel are the performance criteria to identify optimum designs at different Reynolds numbers (Re). The convective flow generated in the 3-D T-type micromixer drastically enhances mixing at Re > 100 by making the two fluids to roll up along the mixing channel. The resulting optimum designs are fabricated on polymethylmethacrylate (PMMA) by CNC micromachining. Experiments are carried out to visualize the streams of de-ionized water and aqueous fluorescein solution, by which the extent of mixing is determined, based on the standard deviation of fluorescein intensities on cross-section images. This study applies a systematic procedure for evaluation and optimization of a proposed 3-D T-mixer which has a configuration of channels that promote convective mixing since the two fluids come into contact. The methodology applied can also be used to efficiently modify and customize current micromixers.

Abstract 1869: Real-Time Three-Dimensional Echocardiography of the Left Atrial Appendage: Initial Experience in Humans with Validation by 64-Slice Computed Tomography

Circulation ◽  
2007 ◽  
Vol 116 (suppl_16) ◽  
Author(s):  
Sanjiv J Shah ◽  
Dianna M Bardo ◽  
Lynn Weinert ◽  
Lissa Sugeng ◽  
Bradley P Knight ◽  
...  
Keyword(s):  
Real Time ◽  
Left Atrial ◽  
Left Atrial Appendage ◽  
Three Dimensional ◽  
Frame Rate ◽  
Atrial Appendage ◽  
Orifice Diameter ◽  
Orifice Area ◽  
2D And 3D ◽  
2D Images

Background: Real-time left atrial appendage (LAA) quantification is increasingly important with the advent of LAA occluder devices for stroke prevention. However, accurate quantification is difficult using 2D-TEE because measurements must be made in multiple views, and LAA orifice cannot be viewed directly. We aimed to determine the accuracy of LAA geometry measured by a new matrix-array (mTEE) probe which can provide unique real-time 3D (RT3D) views of the LAA. Methods: 29 consecutive patients (age 53±18) referred for 2D-TEE underwent additional RT3D-mTEE (Philips ie33; frame rate 8–10/s). The LAA orifice diameter and LAA depth were measured from biplane 2D images, and 2D LAA orifice area was calculated as an ellipse. LAA orifice area and LAA depth were measured in 3D and correlated to 2D. In 8 patients who had cardiac CT available, 2D- and 3D-TEE LAA measurements were correlated with 64-slice CT. All LAA measurements were made at atrial end-diastole. Results: All 29 patients underwent RT3D-mTEE without complication. The LAA was well-visualized in 3D in 26/29 (90%). Because the shape of the LAA orifice in 3D was an ellipsoid with an irregular contour, 2D images resulted in underestimation of area vs. 3D (3.0±1.2 vs. 4.2±2.2 cm 2 ). LAA depth by 2D and 3D correlated well (3.7±0.7 vs. 3.4±0.7; r=0.72, p=0.001). CT LAA orifice area correlated well with 3D-TEE (r=0.98, p<0.0001) but not with 2D-TEE (p=0.78). Conclusions: RT3D-TEE for analysis of LAA geometry is safe and feasible and appears to be more accurate than 2D-TEE. RT3D-TEE provides unique visualization of the LAA orifice in real-time, making it the ideal tool for intra-procedural sizing and placement of LAA occluder devices.

Some Aspects on Inlet Blockage Affecting the Performance of a Heavy Duty Gas Turbine’s Exhaust Diffuser

2014 ◽  
Author(s):  
Philipp Schaefer ◽  
Peter-Anton Gieß ◽  
Conrad Finzel ◽  
Willy H. Hofmann
Keyword(s):  
Secondary Flow ◽  
Gas Turbines ◽  
Effective Area ◽  
Pressure Recovery ◽  
Heavy Duty ◽  
Reduced Pressure ◽  
Core Flow ◽  
The Core ◽  
Inlet Conditions ◽  
The Impact

Exhaust diffusers of heavy duty gas turbines significantly improve the performance of gas turbines. These diffusers typically differ from the simple and well investigated annular or conical diffusers because of the incorporated struts. The investigated model of such a typical exhaust diffuser consists of an annular duct with two rows of integrated struts and a Carnot diffuser downstream of the annular part. In this paper the influence of inlet blockage on the performance of gas turbine diffusers is numerically investigated. 3D-RANS calculations are performed applying the k-ω-SST-model. The numerical inlet conditions for the baseline are given by detailed experimental data acquired in a test rig. The results show that the impact of the inlet blockage on the diffuser flow can be split into two aspects, which both influence diffuser pressure recovery. The first aspect is the well-known reduction of effective area of the core flow leading to reduced pressure recovery feasibility. Secondly, it is observed that the inlet blockage has a significant influence on the structure of secondary flow in the vicinity of the diffuser struts affecting the diffuser pressure recovery. Using a simple correlation of the size of the secondary flow and the core flow the influence on pressure recovery is estimated. In sum, the aerodynamic performance of the annular diffuser and the first row of strut is of high importance and mainly depends on the inlet boundary conditions. Accordingly, these geometries need to be designed to their inlet conditions.

scholarly journals Image Quality Causes Substantial Bias in Three-Dimensional Speckle-Tracking Echocardiography Measures

2018 ◽  
Author(s):  
Lamia Al Saikhan ◽  
Chloe Park ◽  
Alun Hughes
Keyword(s):  
Image Quality ◽  
Ejection Fraction ◽  
Speckle Tracking ◽  
Speckle Tracking Echocardiography ◽  
Three Dimensional ◽  
Poor Quality ◽  
Left Ventricular ◽  
Systematic Bias ◽  
Substantial Bias ◽  
The Impact

BACKGROUND: Three-dimensional speckle-tracking echocardiography (3D-STE) is increasingly used to assess left ventricular (LV) mechanics but the quantitative effect of image quality on measurements is not known. OBJECTIVES: To assess the impact of image quality on 3D-STE derived LV indices. METHODS: Echocardiography was performed in two groups of 18 healthy participants. In the first study, optimal and intentionally poor-quality images were acquired. In the second study, a sheet of ultrasound-attenuating material (neoprene rubber) of three different thicknesses (2, 3 and 4 mm) was used to mimic mildly, moderately and severely impaired image quality respectively. RESULTS: In both studies sub-optimal image quality resulted in a systematic underestimation bias in all LV deformation and rotational indices. LV ejection fraction and volumes were also consistently underestimated. The extent of the bias was proportional to the impairment in image quality (i.e. the poorer the image quality the larger the bias). Reproducibility was also less good for sub-optimal images, although LV volumes and ejection fraction showed excellent reproducibility irrespective of image quality. CONCLUSIONS: Sub-optimal image quality introduces a substantial systematic bias and impairs the reproducibility of 3D-STE. Bias related to image quality might have important clinical implications since its magnitude is similar to that reported in association with disease and may confound associations between disease and LV mechanics.

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