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Zhong L.,Cardiac Mechanics Engineering and Physiology Unit | Zhong L.,3rd Hospital Avenue | Su B.,National University of Singapore | Zhang J.-M.,Cardiac Mechanics Engineering and Physiology Unit | And 4 more authors.
Proceedings of the Annual International Conference of the IEEE Engineering in Medicine and Biology Society, EMBS | Year: 2013

Investigating the intra-ventricular flow is the most important to understand the left ventricular function. In this study, we proposed a fluid-structure interaction (FSI) approach to simulate the blood flow in patient-specific model by combining both mitral and aortic valves. To accommodate the large mesh deformation, moving arbitrary Lagrangian-Eulerian (ALE) meshes were used for moving ventricular wall and rotating leaflets of valves. The left ventricular wall was predescribed according to the points acquired from magnetic resonance image (MRI). Mitral and aortic valves were integrated into the model by assuming each leaflet as a rigid body. Fluid-structure interaction (FSI) approach was adopted to capture the rapid motion of leaflets. The simulation results were qualitatively similar to the measurements reported in literatures. To the best of our knowledge, this is the first to simulate the patient-specific ventricular flow with the presence of both mitral and aortic valves. © 2013 IEEE.


Kabinejadian F.,National University of Singapore | Ghista D.N.,Education Committee | Su B.,Cardiac Mechanics Engineering and Physiology Unit | Kaabi Nezhadian M.,National University of Singapore | And 4 more authors.
Medical Engineering and Physics | Year: 2014

This study documents the superior hemodynamics of a novel coupled sequential anastomoses (SQA) graft design in comparison with the routine conventional end-to-side (ETS) anastomoses in coronary artery bypass grafts (CABG). The flow fields inside three polydimethylsiloxane (PDMS) models of coronary artery bypass grafts, including the coupled SQA graft design, a conventional ETS anastomosis, and a parallel side-to-side (STS) anastomosis, are investigated under pulsatile flow conditions using particle image velocimetry (PIV). The velocity field and distributions of wall shear stress (WSS) in the models are studied and compared with each other. The measurement results and WSS distributions, computed from the near wall velocity gradients reveal that the novel coupled SQA design provides: (i) a uniform and smooth flow at its ETS anastomosis, without any stagnation point on the artery bed and vortex formation in the heel region of the ETS anastomosis within the coronary artery; (ii) more favorable WSS distribution; and (iii) a spare route for the blood flow to the coronary artery, to avoid re-operation in case of re-stenosis in either of the anastomoses. This in vitro investigation complements the previous computational studies of blood flow in this coupled SQA design, and is another necessary step taken toward the clinical application of this novel design. At this point and prior to the clinical adoption of this novel design, in vivo animal trials are warranted, in order to investigate the biological effects and overall performance of this anastomotic configuration in vivo. © 2014 IPEM.


PubMed | Education Committee, National University of Singapore, Nanyang Technological University and Cardiac Mechanics Engineering and Physiology Unit
Type: Journal Article | Journal: Medical engineering & physics | Year: 2014

This study documents the superior hemodynamics of a novel coupled sequential anastomoses (SQA) graft design in comparison with the routine conventional end-to-side (ETS) anastomoses in coronary artery bypass grafts (CABG). The flow fields inside three polydimethylsiloxane (PDMS) models of coronary artery bypass grafts, including the coupled SQA graft design, a conventional ETS anastomosis, and a parallel side-to-side (STS) anastomosis, are investigated under pulsatile flow conditions using particle image velocimetry (PIV). The velocity field and distributions of wall shear stress (WSS) in the models are studied and compared with each other. The measurement results and WSS distributions, computed from the near wall velocity gradients reveal that the novel coupled SQA design provides: (i) a uniform and smooth flow at its ETS anastomosis, without any stagnation point on the artery bed and vortex formation in the heel region of the ETS anastomosis within the coronary artery; (ii) more favorable WSS distribution; and (iii) a spare route for the blood flow to the coronary artery, to avoid re-operation in case of re-stenosis in either of the anastomoses. This in vitro investigation complements the previous computational studies of blood flow in this coupled SQA design, and is another necessary step taken toward the clinical application of this novel design. At this point and prior to the clinical adoption of this novel design, in vivo animal trials are warranted, in order to investigate the biological effects and overall performance of this anastomotic configuration in vivo.


Zhong L.,Cardiac Mechanics Engineering and Physiology Unit | Tan L.K.,Cardiac Mechanics Engineering and Physiology Unit | Finn C.J.,Sir Charles Gairdner Hospital Perth | Ghista D.,Framingham State University | And 2 more authors.
Annals of the Academy of Medicine Singapore | Year: 2012

Introduction: This study was carried out to (i) provide the methodology for determining left atrial (LA) volume, emptying fraction and ejection force (LAEF), from real-time 3-dimensional echocardiography (RT3DE), and (ii) evaluate the effects of age and gender on LA volume and LAEF in a wide age range of healthy participants. Materials and Methods: RT3DE was performed in 102 healthy participants (age range, 20 to 80 years). From full- volume data sets, LA endocardial borders were automatically traced and LA volumes were determined. LAEF was calculated as 1/3×mitral annular area × (blood density) × (peak velocity of A wave)2 according to Newton's law of motion and hydrodynamics; wherein the mitral annular area (MVA) is traced using RT3DE and A is the peak Doppler-derived blood velocity at atrial systole with the sample volume placed at the mitral annulus level. Results: ANOVA analysis revealed that LA volume indices were significantly correlated with age (r = 0.366, P <0.0001 for maximal volume index and r = 0.288, P <0.005 for minimal volume index). LAEF was also significantly positively correlated with age (r =0.49, P <0.0001). The LA emptying fraction was maintained across ages. LA volume indices and LAEF did not differ significantly with gender. Conclusion: Our data can be used as normal reference values for LA volumes and LAEF. We have demonstrated that age is positively related to LA volume indices and LAEF, which suggests that age-dependent cut-off values should be considered in those with heart disease.


Tan M.-L.,Institute of High Performance Computing of Singapore | Su Y.,Institute of High Performance Computing of Singapore | Lim C.-W.,Institute of High Performance Computing of Singapore | Selvaraj S.K.,Institute of High Performance Computing of Singapore | And 2 more authors.
PLoS ONE | Year: 2013

This paper describes an automatic algorithm that uses a geometry-driven optimization approach to restore the shape of three-dimensional (3D) left ventricular (LV) models created from magnetic resonance imaging (MRI) data. The basic premise is to restore the LV shape such that the LV epicardial surface is smooth after the restoration and that the general shape characteristic of the LV is not altered. The Maximum Principle Curvature (k1) and the Minimum Principle Curvature (k2) of the LV epicardial surface are used to construct a shape-based optimization objective function to restore the shape of a motion-affected LV via a dual-resolution semi-rigid deformation process and a free-form geometric deformation process. A limited memory quasi-Newton algorithm, L-BFGS-B, is then used to solve the optimization problem. The goal of the optimization is to achieve a smooth epicardial shape by iterative in-plane and through-plane translation of vertices in the LV model. We tested our algorithm on 30 sets of LV models with simulated motion artifact generated from a very smooth patient sample, and 20 in vivo patient-specific models which contain significant motion artifacts. In the 30 simulated samples, the Hausdorff distances with respect to the Ground Truth are significantly reduced after restoration, signifying that the algorithm can restore geometrical accuracy of motion-affected LV models. In the 20 in vivo patient-specific models, the results show that our method is able to restore the shape of LV models without altering the general shape of the model. The magnitudes of in-plane translations are also consistent with existing registration techniques and experimental findings. © 2013 Tan et al.


Jia X.,Indiana University – Purdue University Indianapolis | Choy J.S.,Indiana University – Purdue University Indianapolis | Zhang Z.-D.,Indiana University – Purdue University Indianapolis | Svendsen M.,Indiana University – Purdue University Indianapolis | And 6 more authors.
Experimental Biology and Medicine | Year: 2013

A load-independent index of myocardial contractility provides a measure of cardiac function. Previous contractility indices have been shown to be either load-dependent or invasive. We sought to determine the extent of load (preload and afterload)-independence of dσ*/dtmax (σ* is pressure-normalized stress) in comparison with other well-established indices. Six anaesthetized pigs underwent left ventricular pressure-volume measurements under various load conditions. The average preload was decreased by 70.0 ± 15.0% (from 39.2 ± 6.4 mL to 11.7 ± 7.7 mL) and increased by 49.3 ± 5.9% (from 35.1 ± 7.4 mL to 51.7 ± 8.9 mL). The average afterload was increased by 74.3 ± 43.5% (from 3.3 ± 0.6 mmHg/mL to 5.7 ± 1.7 mmHg/mL). When preload was reduced within an average of 21.7% (39.2 ± 6.4 mL to 30.7 ± 6.2 mL) using occlusion of the inferior vena cava, dσ*/dtmax did not change significantly (6.50 ± 1.10s-1 vs 6.60 ± 0.90s-1, P = non-significant [NS]). When preload was increased within an average of 29.3% (35.1 ± 7.4 mL to 45.4 ± 7.3 mL) from infusion of normal saline, dσ*/dtmax did not change significantly (7.04 ± 1.00s-1 vs 7.29 ± 1.10s-1, P = NS). When afterload was increased within an average of 42.4% (3.3 ± 0.6 mmHg/mL to 4.7 ± 1.0 mmHg/mL) using intra-aortic balloon occlusion, dσ*/dtmax did not change significantly (6.72 ± 1.18s-1 vs 6.89 ± 1.28s-1, P = NS). As expected, dσ*/dtmax was significantly increased with dobutamine. A linear regression showed no correlation between dσ*/dtmax and preload (r2 = 0.02, P = 0.17) within a maximum range of -30% to +50% of preload change, or between dσ*/dtmax and afterload (r2 = 0.03, P = 0.36) within maximum range of 0-100% of afterload increase, respectively. In conclusion, dσ*/dtmax is independent of loading conditions within an average of 21.7% of preload decrease, 29.3% of preload increase, 42.4% of afterload increase, and sensitive to dobutamine infusion. © 2013 by the Society for Experimental Biology and Medicine.


Zhong L.,Cardiac Mechanics Engineering and Physiology Unit | Gobeawan L.,Institute of High Performance Computing of Singapore | Su Y.,Institute of High Performance Computing of Singapore | Tan J.-L.,National Heart Center | And 4 more authors.
American Journal of Physiology - Heart and Circulatory Physiology | Year: 2012

A quantitative understanding of right ventricular (RV) remodeling in repaired tetralogy of Fallot (rTOF) is crucial for patient management. The objective of this study is to quantify the regional curvatures and area strain based on three-dimensional (3-D) reconstructions of the RV using cardiac magnetic resonance imaging (MRI). Fourteen (14) rTOF patients and nine (9) normal subjects underwent cardiac MRI scan. 3-D RV endocardial surface models were reconstructed from manually delineated contours and correspondence between end-diastole (ED) and end systole (ES) was determined. Regional curvedness (C) and surface area at ED and ES were calculated as well as the area strain. The RV shape and deformation in rTOF patients differed from normal subjects in several respects. Firstly, the curvedness at ED (mean for 13 segments, 0.030 ± 0.0076 vs. 0.029 ± 0.0065 mm-1; P < 0.05) and ES (mean for 13 segments, 0.040 ± 0.012 vs. 0.034 ± 0.0072 mm-1; P < 0.001) was decreased by chronic pulmonary regurgitation. Secondly, the surface area increased significantly at ED (mean for 13 segments, 982 ± 192 vs. 1,397 ± 387 mm2; P < 0.001) and ES (mean for 13 segments, 576 ± 130 vs. 1,012 ± 302 mm2; P < 0.001). In particular, rTOF patients had significantly larger surface area than that in normal subjects in the free wall but not for the septal wall. Thirdly, area strain was significantly decreased (mean for 13 segments, 56 ± 6 vs. 34 ± 7%; P < 0.0001) in rTOF patients. Fourthly, there were increases in surface area at ED (5,726 ± 969 vs. 6,605 ± 1,122 mm2; P < 0.05) and ES (4,280 ± 758 vs. 5,569 ± 1,112 mm2; P < 0.01) and decrease in area strain (29 ± 8 vs. 18 ± 8%; P < 0.001) for RV outflow tract. These findings suggest significant geometric and strain differences between rTOF and normal subjects that may help guide therapeutic treatment. © 2012 the American Physiological Society.


Khalafvand S.S.,Nanyang Technological University | Ng E.Y.-K.,Nanyang Technological University | Zhong L.,Cardiac Mechanics Engineering and Physiology Unit
Proceedings - 2012 International Conference on Biomedical Engineering and Biotechnology, iCBEB 2012 | Year: 2012

This study was to simulate the left ventricular (LV) flow in the human heart via combination of computational fluid dynamics (CFD) and magnetic resonance imaging (MRI). MRI was performed for a heart failure (HF) patient before and 4- month after surgical ventricular restoration. The geometry included LV, left atrium (LA) and ascending aorta derived for 25 frames during one cycle from MRI data. After reconstruction of time dependent geometries and producing intermediate grids, 3D CFD modeling is performed for both before and after surgery. Intermediate geometries are generated to provide fine enough time steps for CFD modeling and discontinue time step fashion is used. The results showed that velocity of blood in LV increased after surgery and more powerful vortices exist than before surgery LV. Combined CFD/MRI for patients before and after surgery with different heart diseases could facilitate better understanding of flow pattern and research into ways to optimize and refine surgical treatment approaches in the future. © 2012 IEEE.


PubMed | Cardiac Mechanics Engineering and Physiology Unit
Type: Journal Article | Journal: American journal of physiology. Heart and circulatory physiology | Year: 2012

A quantitative understanding of right ventricular (RV) remodeling in repaired tetralogy of Fallot (rTOF) is crucial for patient management. The objective of this study is to quantify the regional curvatures and area strain based on three-dimensional (3-D) reconstructions of the RV using cardiac magnetic resonance imaging (MRI). Fourteen (14) rTOF patients and nine (9) normal subjects underwent cardiac MRI scan. 3-D RV endocardial surface models were reconstructed from manually delineated contours and correspondence between end-diastole (ED) and end systole (ES) was determined. Regional curvedness (C) and surface area at ED and ES were calculated as well as the area strain. The RV shape and deformation in rTOF patients differed from normal subjects in several respects. Firstly, the curvedness at ED (mean for 13 segments, 0.030 0.0076 vs. 0.029 0.0065 mm(-1); P < 0.05) and ES (mean for 13 segments, 0.040 0.012 vs. 0.034 0.0072 mm(-1); P < 0.001) was decreased by chronic pulmonary regurgitation. Secondly, the surface area increased significantly at ED (mean for 13 segments, 982 192 vs. 1,397 387 mm(2); P < 0.001) and ES (mean for 13 segments, 576 130 vs. 1,012 302 mm(2); P < 0.001). In particular, rTOF patients had significantly larger surface area than that in normal subjects in the free wall but not for the septal wall. Thirdly, area strain was significantly decreased (mean for 13 segments, 56 6 vs. 34 7%; P < 0.0001) in rTOF patients. Fourthly, there were increases in surface area at ED (5,726 969 vs. 6,605 1,122 mm(2); P < 0.05) and ES (4,280 758 vs. 5,569 1,112 mm(2); P < 0.01) and decrease in area strain (29 8 vs. 18 8%; P < 0.001) for RV outflow tract. These findings suggest significant geometric and strain differences between rTOF and normal subjects that may help guide therapeutic treatment.


PubMed | Cardiac Mechanics Engineering and Physiology Unit
Type: Journal Article | Journal: Annals of the Academy of Medicine, Singapore | Year: 2012

This study was carried out to (i) provide the methodology for determining left atrial (LA) volume, emptying fraction and ejection force (LAEF), from real-time 3-dimensional echocardiography (RT3DE), and (ii) evaluate the effects of age and gender on LA volume and LAEF in a wide age range of healthy participants.RT3DE was performed in 102 healthy participants (age range, 20 to 80 years). From full-volume data sets, LA endocardial borders were automatically traced and LA volumes were determined. LAEF was calculated as 1/3mitral annular area (blood density) (peak velocity of A wave)(2) according to Newtons law of motion and hydrodynamics; wherein the mitral annular area (MVA) is traced using RT3DE and A is the peak Doppler-derived blood velocity at atrial systole with the sample volume placed at the mitral annulus level.ANOVA analysis revealed that LA volume indices were significantly correlated with age (r = 0.366, P <0.0001 for maximal volume index and r = 0.288, P <0.005 for minimal volume index). LAEF was also significantly positively correlated with age (r = 0.49, P <0.0001). The LA emptying fraction was maintained across ages. LA volume indices and LAEF did not differ significantly with gender.Our data can be used as normal reference values for LA volumes and LAEF. We have demonstrated that age is positively related to LA volume indices and LAEF, which suggests that age-dependent cut-off values should be considered in those with heart disease.

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