Effect of a Flared Renal Stent on the Performance of Fenestrated Stent-Grafts at Rest and Exercise Conditions

Purpose: To quantify the hemodynamic impact of a flared renal stent on the performance of fenestrated stent-grafts (FSGs) by analyzing flow patterns and wall shear stress–derived parameters in flared and nonflared FSGs in different physiologic scenarios. Methods: Hypothetical models of FSGs were created with and without flaring of the proximal portion of the renal stent. Flared FSGs with different dilation angles and protrusion lengths were examined, as well as a nonplanar flared FSG to account for lumbar curvature. Laminar and pulsatile blood flow was simulated by numerically solving Navier-Stokes equations. A physiologically realistic flow rate waveform was prescribed at the inlet, while downstream vasculature was modeled using a lumped parameter 3-element windkessel model. No slip boundary conditions were imposed at the FSG walls, which were assumed to be rigid. While resting simulations were performed on all the FSGs, exercise simulations were also performed on a flared FSG to quantify the effect of flaring in different physiologic scenarios. Results: For cycle-averaged inflow of 2.94 L/min (rest) and 4.63 L/min (exercise), 27% of blood flow was channeled into each renal branch at rest and 21% under exercise for all the flared FSGs examined. Although the renal flow waveform was not affected by flaring, flow within the flared FSGs was disturbed. This flow disturbance led to high endothelial cell activation potential (ECAP) values at the renal ostia for all the flared geometries. Reducing the dilation angle or protrusion length and exercise lowered the ECAP values for flared FSGs. Conclusion: Flaring of renal stents has a negligible effect on the time dependence of renal flow rate waveforms and can maintain sufficient renal perfusion at rest and exercise. Local flow patterns are, however, strongly dependent on renal flaring, which creates a local flow disturbance and may increase the thrombogenicity at the renal ostia. Smaller dilation angles, shorter protrusion lengths, and moderate lower limb exercise are likely to reduce the risk of thrombosis in flared geometries

Comparison of blood flow in branched and fenestrated stent-grafts for endovascular repair of abdominal aortic aneurysms.

Purpose: To report a computational study assessing the hemodynamic outcomes of branched stent-grafts (BSGs) for different anatomic variations. Methods: Idealized models of BSGs and fenestrated stent-grafts (FSGs) were constructed with different visceral takeoff angles (ToA) and lateral aortic neck angles. ToA was defined as the angle between the centerlines of the main stent-graft and side branch, with 90° representing normal alignment, and 30° and 120° representing angulated side branches. Computational simulations were performed by solving the conservation equations governing the blood flow under physiologically realistic conditions. Results: The largest renal flow recirculation zones (FRZs) were observed in FSGs at a ToA of 30°, and the smallest FRZ was also found in FSGs (at a ToA of 120°). For straight-neck stent-grafts with a ToA of 90°, mean flow in each renal artery was 0.54, 0.46, and 0.62 L/min in antegrade BSGs, retrograde BSGs, and FSGs, respectively. For angulated stent-grafts, the corresponding values were 0.53, 0.48, and 0.63 L/min. All straight-neck stent-grafts experienced equal cycle-averaged displacement forces of 1.25, 1.69, and 1.95 N at ToAs of 30°, 90°, and 120°, respectively. Angulated main stent-grafts experienced an equal cycle-averaged displacement force of 3.6 N. Conclusion: The blood flow rate in renal arteries depends on the configuration of the stent-graft, with an FSG giving maximum renal flow and a retrograde BSG resulting in minimum renal flow. Nevertheless, the difference was small, up to 0.09 L/min. Displacement forces exerted on stent-grafts are very sensitive to lateral neck angle but not on the configuration of the stent-graft

Hemodynamic Functions of Fenestrated Stent Graft under Resting, Hypertension, and Exercise Conditions.

The aim of this study was to assess the hemodynamic performance of a patient-specific fenestrated stent graft (FSG) under different physiological conditions, including normal resting, hypertension, and hypertension with moderate lower limb exercise. A patient-specific FSG model was constructed from computed tomography images and was discretized into a fine unstructured mesh comprising tetrahedral and prism elements. Blood flow was simulated using Navier-Stokes equations, and physiologically realistic boundary conditions were utilized to yield clinically relevant results. For a given cycle-averaged inflow of 2.08 L/min at normal resting and hypertension conditions, approximately 25% of flow was channeled into each renal artery. When hypertension was combined with exercise, the cycle-averaged inflow increased to 6.39 L/min but only 6.29% of this was channeled into each renal artery, which led to a 438.46% increase in the iliac flow. For all the simulated scenarios and throughout the cardiac cycle, the instantaneous flow streamlines in the FSG were well organized without any notable flow recirculation. This well-organized flow led to low values of endothelial cell activation potential, which is a hemodynamic metric used to identify regions at risk of thrombosis. The displacement forces acting on the FSG varied with the physiological conditions, and the cycle-averaged displacement force at normal rest, hypertension, and hypertension with exercise was 6.46, 8.77, and 8.99 N, respectively. The numerical results from this study suggest that the analyzed FSG can maintain sufficient blood perfusion to the end organs at all the simulated conditions. Even though the FSG was found to have a low risk of thrombosis at rest and hypertension, this risk can be reduced even further with moderate lower limb exercise

Influence of Growth Regulators on Shedding of Broad Bean, Growth, Yield and Seed Quality

In order to study the effect of foliar spraying of growth regulators on growth,seed yield and seed quality, two field experiments were conducted at an extensive field during 2014/2015 and 2015/2016 seasons to determine following foliar spraying of Naphthalene Acetic Acid (NAA) concentrations, i.e. 0, 20, 40 and 60 ppm and Kinetin (Kin) concentrations, i.e. 0, 15, 30 and 45 ppm after 35 and 50 days from sown. Accumulative NAA levelsof to 60 ppm significantly increased total chlorophyll, plant height (cm),branches number/plant, number of shedding flowers, shedding %, pods and seeds number/plant,seedsnumber/pod, seed yield/plant, 100-seed weight (g), seed yield (ton/ha) and protein % in both seasons.Naphthalene Acetic Acid foliar spraying up to 60 ppm exceeded of total chlorophyll, plant height (cm), branchesnumber/plant, number of shedding flowers, podsnumber/plant, seedsnumber/pod, seedsnumber/plant, seed yield (g) /plant, 100-seed weight (g), seed yield (ton/ha) and protein % by 11.47, 23.92, 92.88, 20.53, 11.87, 23.48, 14.16, 24.91, 26.15 and 13.23%, respectively as the average of both seasons. But, reduced the shedding percentage by 11.91% as the average oftwo seasons. Kinetin (Kin) foliar spraying up to 45 ppm significantly increased total chlorophyll, plant height (cm), number of branches/plant, number of shedding flowers, shedding %, pods and seeds number/plant,number of seeds/pod, seed yield/plant, 100-seed weight (g), seed yield (ton/ha) and protein % in both seasons. It could be noticed that foliar spraying of Kinetin (Kin) concentrationsup to 45 ppm exceeded total chlorophyll, plant height (cm), branchesnumber/plant, number of shedding flowers, podsnumber/plant, seedsnumber/pod, seedsnumber/plant, seed yield /plant, 100-seed weight (g), seed yield (ton/ha) and protein % by 12.16, 19.39, 61.64, 5.60, 5.56, 6.96, 5.64, 18.75, 13.38 and 4.39%, respectively as average of both seasons. But, reduced the shedding % by 14.73 % as the average of both seasons.It could be recommended that foliar spraying of Naphthalene Acetic Acid up to 60 ppm and Kin of 45 ppm improved seed yield/ha by 38.2% compared without foliar application

Using the nucleotide substitution rate matrix to detect horizontal gene transfer

BACKGROUND: Horizontal gene transfer (HGT) has allowed bacteria to evolve many new capabilities. Because transferred genes perform many medically important functions, such as conferring antibiotic resistance, improved detection of horizontally transferred genes from sequence data would be an important advance. Existing sequence-based methods for detecting HGT focus on changes in nucleotide composition or on differences between gene and genome phylogenies; these methods have high error rates. RESULTS: First, we introduce a new class of methods for detecting HGT based on the changes in nucleotide substitution rates that occur when a gene is transferred to a new organism. Our new methods discriminate simulated HGT events with an error rate up to 10 times lower than does GC content. Use of models that are not time-reversible is crucial for detecting HGT. Second, we show that using combinations of multiple predictors of HGT offers substantial improvements over using any single predictor, yielding as much as a factor of 18 improvement in performance (a maximum reduction in error rate from 38% to about 3%). Multiple predictors were combined by using the random forests machine learning algorithm to identify optimal classifiers that separate HGT from non-HGT trees. CONCLUSION: The new class of HGT-detection methods introduced here combines advantages of phylogenetic and compositional HGT-detection techniques. These new techniques offer order-of-magnitude improvements over compositional methods because they are better able to discriminate HGT from non-HGT trees under a wide range of simulated conditions. We also found that combining multiple measures of HGT is essential for detecting a wide range of HGT events. These novel indicators of horizontal transfer will be widely useful in detecting HGT events linked to the evolution of important bacterial traits, such as antibiotic resistance and pathogenicity

Evaluating the haemodynamic performance of endografts for complex aortic arch repair

Thoracic endovascular aortic repair (TEVAR) of aortic aneurysms and dissections involving the arch has evolved over the last two decades. Compared to conventional surgical methods, endovascular repair offers a less invasive treatment option with lower risk and faster recovery. Endografts used in TEVAR vary in design depending on the procedure and application. Novel endografts (e.g., branched stent-graft) were developed to ensure perfusion of blood to the supra-aortic vessels, but their haemodynamic performance and long-term durability have not been adequately studied. This review focuses on the use of computational modelling to study haemodynamics in commercially available endografts designed for complex aortic arch repair. First, we summarise the currently adopted workflow for computational fluid dynamics (CFD) modelling, including geometry reconstruction, boundary conditions, flow models, and haemodynamic metrics of interest. This is followed by a review of recently (2010-present) published CFD studies on complex aortic arch repair, using both idealized and patient-specific models. Finally, we introduce some of the promising techniques that can be potentially applied to predict post-operative outcomes

Computational modeling of low-density lipoprotein accumulation at the carotid artery bifurcation after stenting

Restenosis typically occurs in regions of low and oscillating wall shear stress, which also favor the accumulation of atherogenic macromolecules such as low-density lipoprotein (LDL). This study aims to evaluate LDL transport and accumulation at the carotid artery bifurcation following carotid artery stenting (CAS) by means of computational simulation. The computational model consists of coupled blood flow and LDL transport, with the latter being modeled as a dilute substance dissolved in the blood and transported by the flow through a convection-diffusion transport equation. The endothelial layer was assumed to be permeable to LDL, and the hydraulic conductivity of LDL was shear-dependent. Anatomically realistic geometric models of the carotid bifurcation were built based on pre- and post-stent computed tomography (CT) scans. The influence of stent design was investigated by virtually deploying two different types of stents (open- and closed-cell stents) into the same carotid bifurcation model. Predicted LDL concentrations were compared between the post-stent carotid models and the relatively normal contralateral model reconstructed from patient-specific CT images. Our results show elevated LDL concentration in the distal section of the stent in all post-stent models, where LDL concentration is 20 times higher than that in the contralateral carotid. Compared with the open-cell stents, the closed-cell stents have larger areas exposed to high LDL concentration, suggesting an increased risk of stent restenosis. This computational approach is readily applicable to multiple patient studies and, once fully validated against follow-up data, it can help elucidate the role of stent strut design in the development of in-stent restenosis after CAS

The Neurological Morbidity of Carotid Revascularisation: Using Markers of Cellular Brain Injury to Compare CEA and CAS

AimThis comparative study attempts to evaluate the profile of S-100β and Neuron-Specific Enolase (NSE), biomarkers of brain injury, in patients undergoing carotid endarterectomy (CEA) and carotid artery stenting (CAS) and to correlate this with haemodynamic and embolic events detected using trans-cranial Doppler (TCD).Methods52 patients with internal carotid artery stenosis requiring intervention were recruited. 24 patients underwent CAS, and 28 underwent CEA. TCD was performed peri-operatively to record mean Middle Cerebral Artery (MCA) velocity and number of High Intensity Transient Signals (HITS) in the MCA of the operated side. Serum was drawn pre-operatively and at six time points in a 48 hour post-operative period, and then assayed using automated commercial equipment. Within and between group variability in markers were assessed by Generalized Estimation Equations modelling.ResultsCAS caused more HITS (p=0.028) but less haemodynamic disturbance (p=0.0001) than CEA. Treatment modality (CAS versus CEA) had no direct effect on S-100 changes (p=0.467). NSE levels declined after revascularisation in the CAS group but not after CEA (p=0.002). S-100β levels rose in patients who had higher numbers of HITS (p=0.002). S-100β and NSE were not associated with changes in MCA velocity (p>0.5). S-100β alone increased significantly at 24 hours in those patients with a post-operative neurological deficit (p=0.015).ConclusionsTrans-cranial Doppler findings suggest that the mechanisms of rise in S-100β and NSE levels may differ and may be due to increased peri-operative micro-embolisation and cerebral hypoperfusion respectively. Further studies are required to assess the clinical significance of these observed changes