Suture Line Response of End-to-Side Anastomosis: A Stress Concentration Methodology
Abstract End-to-side vascular anastomosis has a considerable complexity regarding the suturing of the juncture line between the artery and the graft. The present study proposes a stress–concentration methodology for the prediction of the stress distribution at the juncture line, aiming to provide generic expressions describing the response of an end-to-side anastomosis. The proposed methodology is based on general results obtained from the analysis of pipe connections, a topic that has been investigated in recent years in the field of offshore structural engineering. A key aspect for implementing the stress&...
Source: Cardiovascular Engineering and Technology - December 10, 2014 Category: Cardiology Source Type: research

Pulse Wave Velocity Prediction and Compliance Assessment in Elastic Arterial Segments
Abstract Pressure wave velocity (PWV) is commonly used as a clinical marker of vascular elasticity. Recent studies have increased clinical interest in also analyzing the impact of heart rate, blood pressure, and left ventricular ejection time on PWV. In this article we focus on the development of a theoretical one-dimensional model and validation via direct measurement of the impact of ejection time and peak pressure on PWV using an in vitro hemodynamic simulator. A simple nonlinear traveling wave model was developed for a compliant thin-walled elastic tube filled with an incompressible fluid. This model accounts ...
Source: Cardiovascular Engineering and Technology - December 6, 2014 Category: Cardiology Source Type: research

A Technical Review of Minimally Invasive Mitral Valve Replacements
Abstract Mitral regurgitation is one of the most common forms of heart valve disorder, which may result in heart failure. Due to the rapid ageing of the population, surgical repair and replacement treatments, which have represented an effective treatment in the past, are now unsuitable for about half of symptomatic patients, who are judged high-risk. Encouraged by the positive experience with transcatheter aortic valves and percutaneous reconstructive mitral treatments, a number of research groups are currently engaged in the development of minimally invasive approaches for the functional replacement of the mitral...
Source: Cardiovascular Engineering and Technology - November 25, 2014 Category: Cardiology Source Type: research

Variation in Cardiac Pulse Frequencies Modulates vSMC Phenotype Switching During Vascular Remodeling
Abstract In vitro perfusion systems have exposed vascular constructs to mechanical conditions that emulate physiological pulse pressure and found significant improvements in graft development. However, current models maintain constant, or set pulse/shear mechanics that do not account for the natural temporal variation in frequency. With an aim to develop clinically relevant small diameter vascular grafts, these investigations detail a perfusion culture model that incorporates temporal pulse pressure variation. Our objective was to test the hypothesis that short-term variation in heart rate, such as chan...
Source: Cardiovascular Engineering and Technology - November 18, 2014 Category: Cardiology Source Type: research

Comparative Study of Degradation Behavior of Bioresorbable Cardiovascular Scaffolds
Abstract This comparative study investigated the biodegradation behavior and mechanism of bioresorbable cardiovascular scaffolds using bench testing under physiological conditions and in vivo experiment. The results show that the molecular weight of the scaffold decreased with respect to time after implantation in both in vivo and in vitro tests. It was found that the molecular weights of the implanted scaffolds in the in vivo and in vitro models decreased to 61.8 and 68.5% respectively 6 months after implantation, but the thermodynamic properties of the scaffold material were not significantly affected by th...
Source: Cardiovascular Engineering and Technology - November 11, 2014 Category: Cardiology Source Type: research

Asymptotic Model of Fluid–Tissue Interaction for Mitral Valve Dynamics
Abstract The vortex formation process inside the left ventricle is intrinsically connected to the dynamics of the mitral leaflets while they interact with the flow crossing the valve during diastole. The description of the dynamics of a natural mitral valve still represents a challenging issue, especially because its material properties are not measurable in vivo. Medical imaging can provide some indications about the geometry of the valve, but not about its mechanical properties. In this work, we introduce a parametric model of the mitral valve geometry, whose motion is described in the asymptotic limit under the...
Source: Cardiovascular Engineering and Technology - November 7, 2014 Category: Cardiology Source Type: research

Improvement of Left Ventricular Asynchrony: Cases of Functional Recovery After Revascularization
Abstract Assessment of regional contraction is considered important for diagnosis of coronary artery disease (CAD). We evaluated the synchronicity in regional contraction and assessed recovery from contraction insufficiency after revascularizations. Myocardial contraction parallel to the left ventricular (LV) wall was calculated using the method called quantification of segmental function by solving the Poisson equation (QSFP) from an electrocardiogram (ECG)-gated 99mTc-methoxyisobutylisonitrile (MIBI) single-photon emission computed tomographic (ECG-SPECT) image. Myocardial synchronous contraction was quantified ...
Source: Cardiovascular Engineering and Technology - November 5, 2014 Category: Cardiology Source Type: research

Co-localization of Disturbed Flow Patterns and Occlusive Cardiac Allograft Vasculopathy Lesion Formation in Heart Transplant Patients
Abstract Cardiac allograft vasculopathy (CAV) is one of the leading causes of morbidity and morality in orthotopic heart transplant (HTx) patients. While disturbed flow patterns have been linked to the spatial localization of atherosclerosis, the role of hemodynamics in CAV development has not been examined. HTx patients (n = 5) requiring percutaneous coronary intervention (PCI) for a focal, epicardial lesion were studied. Angiographic images were retrospectively obtained from baseline (i.e., in the presence of no observed disease) and follow-up catheterizations (i.e., at the time of PCI; 12.4 &plus...
Source: Cardiovascular Engineering and Technology - October 28, 2014 Category: Cardiology Source Type: research

Differential Aortic and Mitral Valve Interstitial Cell Mineralization and the Induction of Mineralization by Lysophosphatidylcholine In Vitro
This study was undertaken to examine the role of the lipid lysophosphatidylcholine (LPC) in a comparison of aortic and mitral valve cellular mineralization. The proportion of LPC in differentially calcified regions of diseased aortic valves was determined using thin layer chromatography (TLC). Next, porcine valvular interstitial cells (pVICs) from the aortic (paVICs) and mitral valve (pmVICs) were cultured with LPC (10−1–105 nM) and analyzed for cellular mineralization, alkaline phosphatase activity (ALPa), proliferation, and apoptosis. TLC showed a higher percentage of LPC in calcified regions of tissue c...
Source: Cardiovascular Engineering and Technology - October 7, 2014 Category: Cardiology Source Type: research

Bench Models for Assessing the Mechanics of Mitral Valve Repair and Percutaneous Surgery
Abstract Rapid preclinical evaluations of mitral valve (MV) mechanics are currently best facilitated by bench models of the left ventricle (LV). This review aims to provide a comprehensive assessment of these models to aid interpretation of their resulting data, inform future experimental evaluations, and further the translation of results to procedure and device development. For this review, two types of experimental bench models were evaluated. Rigid LV models were characterized as fluid-mechanical systems capable of testing explanted MVs under static and or pulsatile left heart hemodynamics. Passive LV models w...
Source: Cardiovascular Engineering and Technology - September 30, 2014 Category: Cardiology Source Type: research

Fabrication and Evaluation of Nitinol Thin Film Heart Valves
Abstract In recent years new innovations improved the technology of devices for transcatheter heart valve replacement. In order to fabricate an efficient, durable, less thrombogenic and very thin heart valved stent for transcatheter implantation, heart valve leaflets of Nitinol (NiTi) thin film were developed. This work presents a method to fabricate NiTi thin film leaflets for transcatheter aortic valve replacements. NiTi valve leaflets were fabricated in different film thicknesses (10, 15 and 20 µm) by magnetron sputter deposition and a subsequent forming process. Pulsatile testing was performed to in...
Source: Cardiovascular Engineering and Technology - September 19, 2014 Category: Cardiology Source Type: research

Engineering Angiogenesis for Myocardial Infarction Repair: Recent Developments, Challenges, and Future Directions
Abstract Myocardial infarction is a cardiovascular disorder that remains a critical health issue worldwide. Because of its intrinsic inability to regenerate, cardiac tissue fails to repair itself after myocardial infarction. Cardiovascular engineering is a promising approach to regenerating myocardium for myocardial infarction repair. Despite explosive growth in research and interest in this field, cardiovascular regenerative medicine faces many challenges, with the need for rapid vascularization being the most pressing. Due to the high metabolic demand of cardiac cells, myocytes transplanted or implanted via card...
Source: Cardiovascular Engineering and Technology - September 4, 2014 Category: Cardiology Source Type: research

Influence of an Arterial Stenosis on the Hemodynamics Within an Arteriovenous Fistula (AVF): Comparison Before and After Balloon-Angioplasty
The objective is to investigate their influence on the hemodynamic conditions within the AVF. A numerical simulation of the blood flow is conducted within a patient-specific arteriovenous fistula that presents an 60% stenosis on the inflow artery. In order to find the vessel shape without stenosis and compare the flow conditions with and without stenosis, the endovascular treatment of balloon-angioplasty is simulated by modeling the vessel deformation during balloon inflation implicitly. Clinically, balloon-angioplasty is considered successful if the post-treatment residual degree of stenosis is below 30%. Different balloo...
Source: Cardiovascular Engineering and Technology - September 1, 2014 Category: Cardiology Source Type: research

Influence of Thermal Annealing on the Mechanical Properties of PLLA Coiled Stents
Abstract To investigate the influence of elevated annealing temperature (70–90 °C) on the mechanical properties of coiled helical PLLA stents. PLLA 0.10 mm fibers and Ø3 mm × 12 mm stents were fabricated and annealed at 70, 80 and 90 °C for 25 min. The mechanical properties of the fibers and the functional characteristics of the stents were measured and compared to a control group processed at 21 °C. The stents were mounted, expanded and relaxed using an Ø3 mm × 2 cm balloon catheter to a maximum balloon p...
Source: Cardiovascular Engineering and Technology - September 1, 2014 Category: Cardiology Source Type: research

Effect of Calcification Modulus and Geometry on Stress in Models of Calcified Atherosclerotic Plaque
This study investigated the effects of E calc and calcification geometry on stress in models of atherosclerotic plaque, with the modifying factor of fibrous component constitutive relation. Stress was calculated in idealized plane-strain finite element models of pressurized coronary arteries containing calcified lesions. Lesions were modeled as arc-shaped, circular, and elliptical regions with varying lumen separation, length, and thickness. E calc varied from 1.0 MPa to 10 GPa. Various orthotropic and hyperelastic constitutive relations for arterial wall and fibrous plaque were assigned, re...
Source: Cardiovascular Engineering and Technology - September 1, 2014 Category: Cardiology Source Type: research

A Review of Catheter Related Complications During Minimally Invasive Transcatheter Cardiovascular Intervention with Implications for Catheter Design
The objectives of this study are to identify the most important complications associated with transcatheter cardiovascular intervention and to obtain insights into those complications which are directly related to mechanical interaction between the blood vessel and the catheter, by performing a literature review. Using the insights gained, several generic strategies for improving catheter design to minimize mechanical interaction are proposed, which are aimed at reducing complication prevalence and mortality during transcatheter cardiovascular intervention. Data were gathered from the literature on complications associated...
Source: Cardiovascular Engineering and Technology - September 1, 2014 Category: Cardiology Source Type: research

Improving Blood Flow Simulations by Incorporating Measured Subject-Specific Wall Motion
This article shows that it is feasible to include measured subject-specific wall motion into numerical simulations, and that the wall motion greatly affects the flow field. This approach to incorporate measured motion should be considered in future studies of arterial blood flow simulations. (Source: Cardiovascular Engineering and Technology)
Source: Cardiovascular Engineering and Technology - September 1, 2014 Category: Cardiology Source Type: research

A Stent with Customizable Length for Treatment of Critical Limb Ischemia: Clinical Need, Device Development and Pre-clinical Testing
This study describes a unique multi-segmented self-expanding stent developed specifically for use in infrapopliteal revascularization procedures. The number of segments deployed can be selected to optimize the stented length and location. The device may provide an adjunctive treatment in instances of sub-optimal balloon angioplasty when treating CLI. The clinical opportunity for the device is presented, followed by a description of the design and the design process. The results from a range of bench testing are presented as well as the findings of porcine studies to assess in vivo behaviour. In summary, while further devel...
Source: Cardiovascular Engineering and Technology - August 28, 2014 Category: Cardiology Source Type: research

The ‘Sphere’: A Dedicated Bifurcation Aneurysm Flow-Diverter Device
We present flow-based results from the early stage design cycle, based on computational modeling, of a prototype flow-diverter device, known as the ‘Sphere’, intended to treat bifurcation aneurysms of the cerebral vasculature. The device is available in a range of diameters and geometries and is constructed from a single loop of NITINOL® wire. The ‘Sphere’ reduces aneurysm inflow by means of a high-density, patterned, elliptical surface that partially occludes the aneurysm neck. The device is secured in the healthy parent vessel by two armatures in the shape of open loops, resulting in negligibl...
Source: Cardiovascular Engineering and Technology - August 26, 2014 Category: Cardiology Source Type: research

Characterization of Regional Deformation and Material Properties of the Intact Explanted Vein by microCT and Computational Analysis
This study presents a novel method for characterizing deformation of the intact explanted vein under physiological loads and determining its material properties by combining high-resolution imaging and computational analysis. High-resolution CT (microCT) was used to image an iodine-stained, excised porcine internal jugular vein sample under extension to 100 and 120% of in situ length, and inflation and 2, 10, 20 mmHg of pressure, inside a microCT-compatible hydrostatic loading chamber. Regional strains were measured with the finite element (FE) image registration method known as Hyperelastic Warping. Material properti...
Source: Cardiovascular Engineering and Technology - August 26, 2014 Category: Cardiology Source Type: research

A Low-Order Parametric Description of Left Ventricular Kinematics
Abstract An approximate description for the deformation of the left ventricle (LV) throughout the cardiac cycle is developed in terms of three time-dependent parameters. The reference configuration, corresponding to end-diastole, is represented as a thick-walled prolate spheroid. By using prolate spheroidal coordinates, a three-parameter family of mappings is defined to represent the deformed shapes of the LV wall, while identically conserving wall volume. The three parameters represent lengthening with constant internal volume, contraction with reduction of internal volume, and torsion. Feasibility is illustrated...
Source: Cardiovascular Engineering and Technology - August 20, 2014 Category: Cardiology Source Type: research

Inverse Solution of the Fetal-Circulation Model Based on Ultrasound Doppler Measurements
Abstract Fetal growth restriction (FGR) is one of the major contributors to adverse perinatal outcome. However, the diagnostic tools used for the assessment of fetal well-being are limited due to the great variability among fetuses. The purpose of this study was to estimate the dynamics of fetal circulation during the advanced stages of the gestational period. A methodology for estimating fetal hemodynamic parameters is presented. The method combines a mathematical model of the fetal circulation, optimization algorithm, and measurements of power-Doppler ultrasound. The model estimates fetal indices of the fetal c...
Source: Cardiovascular Engineering and Technology - June 1, 2014 Category: Cardiology Source Type: research

Contribution of Mechanical and Fluid Stresses to the Magnitude of In-stent Restenosis at the Level of Individual Stent Struts
This study reports an investigation of the correlation between stresses obtained from computational simulations with the magnitude of ISR at the level of individual stent struts observed in an in vivo model of restenosis. Structural and fluid dynamic analyses were undertaken in a model based on volumetric micro-CT data from an in vivo stent deployment in a porcine right coronary artery. Structural and fluid mechanics were compared with histological data from the same stented vessel sample. Interpretation of the combined data at the level of individual stent struts was possible by identifying the location of each 2-D histol...
Source: Cardiovascular Engineering and Technology - June 1, 2014 Category: Cardiology Source Type: research

In Vitro Validation of Patient-Specific Hemodynamic Simulations in Coronary Aneurysms Caused by Kawasaki Disease
This study demonstrated that CFD produced good qualitative and quantitative predictions of velocities in a realistic coronary aneurysm anatomy under physiological flow conditions. The results provide insights on factors that may influence the level of agreement, and a set of in vitro experimental data that can be used by others to compare against CFD simulation results. The findings of this study increase confidence in the use of CFD for investigating hemodynamics in the specialized anatomy of coronary aneurysms. This provides a basis for future hemodynamics studies in patient-specific models of Kawasaki disease. (Source: ...
Source: Cardiovascular Engineering and Technology - June 1, 2014 Category: Cardiology Source Type: research

High Shear Thrombus Formation under Pulsatile and Steady Flow
Abstract Most previous studies have investigated in vitro thrombus formation under steady flow conditions at physiological shear rates, though occlusive thrombosis leading to myocardial infarction and stroke forms under elevated shear rates and pulsatile flow. Two reports of pulsatile flow on thrombosis have yielded conflicting results. In the present study, we quantify the effect of very high shear, reversing pulsatile flow relevant to coronary thrombosis on platelet deposition leading to occlusive thrombus formation. Whole porcine blood was perfused in a collagen-coated, tubular, stenotic test section under pul...
Source: Cardiovascular Engineering and Technology - June 1, 2014 Category: Cardiology Source Type: research

Investigating the Effect of Blood Sample Volume in the Chandler Loop Model: Theoretical and Experimental Analysis
This study proposes a new criterion for determining sample volume and defines a time-averaged wall shear stress equation for this model. In vitro experiments were performed to investigate the implications of sample volume on blood cell activation in the presence of model stent. Experimental results indicated that in the absence of a stent and for shear stress up to about 56 dyn/cm2, platelet activation was independent of volume and shear. On the other hand, the formation of platelet–leukocyte aggregates was affected by volume as well as the presence of a stent. Doubling blood volume for the same stent resulted i...
Source: Cardiovascular Engineering and Technology - June 1, 2014 Category: Cardiology Source Type: research

Predicting Outcome of Aortic Dissection with Patent False Lumen by Computational Flow Analysis
Abstract Although Type B aortic dissection (AoD) has better in-hospital survival than Type A AoD, the short- and long term outcome for patients remains challenging, with 50–80% deaths at 5-years. Dissection-related complications include rapid aortic expansion, impending rupture, and malperfusion syndromes. We aimed to assess hemodynamic implications of patients with patent false lumen (FL) of dissected aorta. Computational fluid dynamic analyses were performed on patient-specific aortic geometries reconstructed from computed tomography scans of 25 patients with AoDs, who were admitted in our hospital from 2...
Source: Cardiovascular Engineering and Technology - June 1, 2014 Category: Cardiology Source Type: research

Endothelial Cells Modulate Platelet Response to Dynamic Shear Stress
Abstract The goal of this study was to investigate how endothelial cells affect platelet response to physiologically relevant dynamic shear stress. In a cone and plate shearing device, washed platelets were exposed to constant (0.1, 0.3, 1, and 3 Pa) or dynamic (normal, low and temporally elevated) shear stress waveforms with or without the presence of endothelial cells. Platelet surface CD62P, CD42b and CD41a expression was measured using flow cytometry. Endothelial cell surface ICAM-1 and vWF expression was measured using ELISA, endothelial cell surface PECAM-1 expression was measured using fluorescence mi...
Source: Cardiovascular Engineering and Technology - June 1, 2014 Category: Cardiology Source Type: research

Quantitative Evaluation of Annuloplasty on Mitral Valve Chordae Tendineae Forces to Supplement Surgical Planning Model Development
Abstract Computational models of the heart’s mitral valve (MV) exhibit potential for preoperative surgical planning in ischemic mitral regurgitation (IMR). However challenges exist in defining boundary conditions to accurately model the function and response of the chordae tendineae to both IMR and surgical annuloplasty repair. Towards this goal, a ground-truth data set was generated by quantifying the isolated effects of IMR and mitral annuloplasty on leaflet coaptation, regurgitation, and tethering forces of the anterior strut and posterior intermediary chordae tendineae. MVs were excised from ovine heart...
Source: Cardiovascular Engineering and Technology - March 1, 2014 Category: Cardiology Source Type: research

Energy Costs of Singular and Concomitant Pressure and Volume Overload Lesions
The objective of this study is to propose a theoretical framework to utilize the ventricular power overhead rates of HT, aortic regurgitation (AR), aortic stenosis (AS), and mitral regurgitation (MR) as a new means to assess severity, particularly under concomitant conditions. A lumped parameter model was utilized to evaluate the ventricular energy budget under normal, singular, and concomitant combinations of HT, AS, AR, and MR; and calculate energy overhead rate defined as the % increase in ventricular power output. Disease severity for each lesion was modeled at mild, moderate, and severe levels per AHA/ACC guidelines. ...
Source: Cardiovascular Engineering and Technology - March 1, 2014 Category: Cardiology Source Type: research