Altered Flow Patterns Research Articles

A high-order, fully coupled, upwind, compact discontinuous Galerkin method for modeling of viscous fingering in compressible porous media

We present a new approach for high-fidelity compressible porous media simulations. Our method is based on a fully coupled, upwind, high-order discontinuous Galerkin formulation of the equations of miscible displacement transport. A key feature of the proposed method is the high level of flexibility to compute complex subsurface geometries, maintaining full order of accuracy. The present formulation solves pressure and transport equations in a fully coupled fashion and, as a result, can capture the strong interaction between pressure and concentrations of injected components in highly compressible media. The proposed method also shows very low sensitivity to mesh orientation, in contrast with classical finite volume approximations used in porous media flow simulations. The robustness and accuracy of the method are demonstrated in a number of challenging compressible and incompressible multiphase flow problems. Numerical simulations also reveal interesting phenomena associated with high pore compressibility, such as the reduction of the growth rate of viscous fingers and the alteration of flow patterns near impermeable obstacles. Additional computations performed with an anisotropic permeability tensor reveal that, somewhat against intuition, viscous fingers have a preferential growth along the direction of low permeability.

Measurement of retinal blood flow rate in diabetic rats: disparity between techniques due to shunting of capillary flow

The objective of this study was to clarify whether retinal blood flow (RBF) rates are altered in rats during streptozotocin (STZ)‐induced diabetes. Reports of this possibility in the literature are mixed, possibly due to the different techniques used to measure RBF. STZ (or vehicle alone, in controls) was injected into the rats (30 mg/kg for 3 days) to induce a model of type I diabetes. Eight weeks later, RBF rates were measured in the anesthetized rats using intravital microscopy and a fluorescent tracer (FITC‐dextran) in a mean circulation (transit) time index of flow. In separate rats, RBF was measured using a microsphere infusion technique. The induction of diabetes resulted in a 30–35% decrease in RBF (***p<0.001) in the STZ rats as determined by the microsphere measurement. However, in a striking contrast to these results, the mean transit times of injected FITC‐dextran were ~3× faster in the STZ rats compared with the controls (**p<0.01). We hypothesize that this discrepancy is due to shunting of RBF away from the deep retinal capillary layers in the STZ rats, with the altered flow pattern allowing the rapid transit of tracer from the arterioles into the venules. Funded by NIH EY017599 (NRH).

The influence of bicuspid aortic valves on the dynamic pressure distribution in the ascending aorta – a Porcine Ex-vivo Model

OBJECTIVES: The aim of the study was to simulate the effect of different bicuspid aortic valve configurations on the dynamic pressure distribution in the ascending aorta. METHODS: Aortic specimens were harvested from adult domestic pigs. In Group 1, bicuspidalization was created by a running suture between the left and the right coronary leaflets (n= 6) and in Group 2 by a running suture between the left and the non-coronary leaflets (n= 6). Eleven tricuspid specimens served as controls. Two intraluminal pressure catheters were positioned at the concavity and the convexity of the ascending aorta. The specimens were connected to a mock circulation (heart rate: 60 bpm, target pressure: 95 mmHg). A comparison of the different conditions was also done in a numerical simulation. RESULTS: At a distal mean aortic pressure of 94 ± 10 mmHg, a mean flow rate of 5.2 ± 0.3 l/min was achieved. The difference of maximal dynamic pressure values (which occurred in systole) between locations at the convexity and the concavity was 7.8 ± 2.9 mmHg for the bicuspid and 1.0 ± 0.9 mmHg for the tricuspid specimens (P< 0.001). The numerical simulation revealed an even higher pressure difference between convexity and concavity for bicuspid formation. CONCLUSIONS: In this hydrodynamic mock circulation model, we were able to demonstrate that bicuspid aortic valves are associated with significant pressure differences in different locations within the ascending aorta compared with tricuspid aortic valves. These altered pressure distributions and flow patterns may further add to the understanding of aneurismal development in patients with bicuspid aortic valves and might serve to anticipate adverse aortic events due to a better knowledge of the underlying mechanisms.

Wall shear stress and flow patterns in the ascending aorta in patients with bicuspid aortic valves differ significantly from tricuspid aortic valves: a prospective study

We compared flow and wall shear stress (WSS) patterns in the ascending aorta of individuals with either bicuspid aortic valve (BAV) or tricuspid aortic valve (TAV) using four-dimensional cardiovascular magnetic resonance (4D-CMR). BAV are known to be associated with dilation and dissection of the ascending aorta. However, the cause of vessel disease in patients with BAVs is unknown. Inborn connective tissue disease and also dilation secondary to increased WSS because of altered blood flow patterns in the ascending aorta are discussed as causes for dilation of the aorta. WSS can be estimated non-invasively by 4D-CMR. Eighteen, otherwise, healthy individuals with functionally normal BAVs were compared prospectively with an age- and sex-matched control group of healthy individuals with TAV. Blood flow data were obtained by 4D-CMR visualization and WSS was calculated with specific software tools. Eighty-five per cent of the individuals with BAVs showed a high-grade helical flow pattern in the ascending aorta compared with 6% of the individuals with TAV. WSS in the ascending aorta was significantly altered in individuals with BAVs compared with TAV. WSS and flow patterns in the ascending aorta in patients with BAVs without concomitant valve or vessel disease are significantly different compared with TAV. The significantly higher shear forces may have an impact on the development of aortic dilation in patients with BAVs.

Effects of aging and exercise training on skeletal muscle blood flow and resistance artery morphology

With old age, blood flow to the high-oxidative red skeletal muscle is reduced and blood flow to the low-oxidative white muscle is elevated during exercise. Changes in the number of feed arteries perforating the muscle are thought to contribute to this altered hyperemic response during exercise. We tested the hypothesis that exercise training would ameliorate age-related differences in blood flow during exercise and feed artery structure in skeletal muscle. Young (6-7 mo old, n = 36) and old (24 mo old, n = 25) male Fischer 344 rats were divided into young sedentary (Sed), old Sed, young exercise-trained (ET), and old ET groups, where training consisted of 10-12 wk of treadmill exercise. In Sed and ET rats, blood flow to the red and white portions of the gastrocnemius muscle (Gast(Red) and Gast(White)) and the number and luminal cross-sectional area (CSA) of all feed arteries perforating the muscle were measured at rest and during exercise. In the old ET group, blood flow was greater to Gast(Red) (264 ± 13 and 195 ± 9 ml · min(-1) · 100 g(-1) in old ET and old Sed, respectively) and lower to Gast(White) (78 ± 5 and 120 ± 6 ml · min(-1) · 100 g(-1) in old ET and old Sed, respectively) than in the old Sed group. There was no difference in the number of feed arteries between the old ET and old Sed group, although the CSA of feed arteries from old ET rats was larger. In young ET rats, there was an increase in the number of feed arteries perforating the muscle. Exercise training mitigated old age-associated differences in blood flow during exercise within gastrocnemius muscle. However, training-induced adaptations in resistance artery morphology differed between young (increase in feed artery number) and old (increase in artery CSA) animals. The altered blood flow pattern induced by exercise training with old age would improve the local matching of O(2) delivery to consumption within the skeletal muscle.

Characterizing Diffusion and Transport in Microfluidics Channels: A Combined Raman Microscopy and Band-Target Entropy Minimization Study

With the increasing use of microfluidics, there is a need for a rather general experimental approach in order to monitor and characterize transport effects. Indeed, micro-fabrication methods have allowed the inclusion of numerous new structures and devices within microfluidics channels, and such alterations in flow patterns should impact solute transport characteristics. In the present contribution, Raman microscopy is combined with band-target entropy minimization analysis (BTEM) in order to rapidly assess and map concentration profiles in various regions of a microfluidics device. Two isotopomers, CHCl(3) and CDCl(3), are contacted under laminar conditions. Special consideration is given to the point of contact between the two liquids, transport in straight sections, transport in curved sections, and wall effects. Break-through curves confirmed that stagnation of fluid at the wall is not occurring, despite substantial wall roughness. Since the methods used in the present study are quite general, they should be useful in rapidly accessing transport effects when fluids (also in conjunction with colloids, suspensions, and solids) are contacted in the presence of both simple as well as complex geometries.

Left-sided Pulmonary Venous Pathway Obstruction after Mustard Operation

Pulmonary venous pathway obstruction (PVPO) is a serious complication of the atrial switch procedure for transposition of the great arteries (TGA). Redistribution of pulmonary arterial blood flow may make conventional echocardiographic measures of unilateral PVPO difficult to interpret. Previous studies have demonstrated altered arterial flow patterns using phase-contrast magnetic resonance imaging (PC-MRI). The purpose of this study was to investigate arterial flow patterns in the setting of unilateral PVPO following the Mustard operation. We retrospectively reviewed the arterial flow patterns of 12 patients undergoing magnetic resonance imaging between 2006 and 2011 who had had the Mustard operation. Three patients had left PVPO and all showed >65% flow distributed to the right pulmonary artery (RPA). One had severe obstruction and was the only one to show significant continuous diastolic forward flow in the RPA or diastolic flow reversal in the left pulmonary artery. RPA/left pulmonary artery flow ratio appears to be a sensitive marker for PVPO. In the absence of pulmonary regurgitation, reversed diastolic flow in the ipsilateral and continuous in the contralateral pulmonary artery appears specific for severe obstruction. Branch pulmonary artery phase-contrast magnetic resonance imaging (PC-MRI) should be performed routinely for patients who have had an atrial switch for transposition of the great arteries.

Four-dimensional, flow-sensitive magnetic resonance imaging of blood flow patterns in thoracic aortic dissections

The purpose of this study was to evaluate alterations in flow patterns in thoracic aortic dissections using 4-dimensional, flow-sensitive magnetic resonance imaging. This prospective study was conducted at 2 academic tertiary referral medical centers. Thirteen 4-dimensional flow magnetic resonance imaging studies were performed in 12 subjects (4 female, aged 25-71 years) with thoracic aortic dissection using 3.0T clinical scanners. Qualitative assessment of flow patterns in the true and false lumina was performed in consensus by 3 cardiovascular radiologists. Quantitative analysis included measurement of net flow, retrograde flow, peak flow, and time-to-peak flow in the true and false lumina in the ascending aorta, aortic arch, and descending aorta. Differences in flow through the true and false lumina at each analysis plane were compared with the 2-tailed, paired Student t test. Flow patterns were significantly altered in association with different extents of disease, vessel dilatation, and post-therapeutic anatomy. Total flow per cardiac cycle and peak flow were higher in the true lumen than in the false lumen (P<.01). Retrograde flow was less in the true lumen than in the false lumen (P≤.01). Time-to-peak flow in the true lumen occurred later than in the false lumen (P=.05-.08). Four-dimensional, flow-sensitive magnetic resonance imaging at 3.0T provided qualitative and quantitative information on alterations of aortic flow in patients with thoracic aortic dissection. Future application of this magnetic resonance flow methodology may help provide insights into the pathophysiology and effects of flow alterations and establish prognostic indicators for the development of complications or aneurysm growth in patients with aortic dissection.

Dialysis Access Flow Phenomenon Demonstrated via an Internal Jugular Central Venous Catheter Uniquely Positioned within a Superior Vena Cava Stenosis

Dialysis Access Flow Phenomenon Demonstrated <i>via</i> an Internal Jugular Central Venous Catheter Uniquely Positioned within a Superior Vena Cava Stenosis

MORE EXOTIC AND FEWER NATIVE PLANT SPECIES: RIVERINE VEGETATION PATTERNS ASSOCIATED WITH ALTERED SEASONAL FLOW PATTERNS

ABSTRACTNatural flow regimes are important for sustaining riverine vegetation. The regulation of river flows to provide water for agriculture often results in changes to flow timing. This study assesses the impact of altered seasonal flow patterns on riverine flora.Within temperate Australia, we surveyed the vegetation of five lowland rivers, three of which have large dams that alter their seasonal flow patterns; the other two are unregulated. From four to six sites were selected on each river, and these were classified into three levels of regulation based on the extent to which the timing of their seasonal flow patterns were altered. Sites were surveyed in winter and the following summer. Permanent quadrats were also established at a number of the surveyed sites and resurveyed every 3 months.Of the 267 plant taxa identified, 145 were exotic (non‐native). More exotic taxa and fewer native taxa were associated with increasing level of seasonal flow inversion (regulation). In particular, greater numbers of short‐lived exotic terrestrial taxa and fewer native woody taxa were associated with increasing level of regulation. Some exotic woody species (e.g. willows) were more common in the unregulated rivers and may have life‐history traits favoured by the natural seasonal flow patterns of study area. Multivariate analyses showed that level of regulation had a significant effect on the overall composition of the riverine vegetation.Our results provide support for the hypotheses that flow regulation adversely affects native species diversity and increases the vulnerability of riparian zones to invasion by exotic species; however, these effects are dependent on plant species' life‐history strategies. Our study highlights the importance of natural seasonal flow patterns for sustaining native riverine plant communities. Flow management aimed at maintaining or restoring ecological values should consider seasonal flow patterns. Winter/spring flow peaks may be particularly important for the recruitment of native riverine plants, especially trees and shrubs, and reducing the extent of exotic annuals and grasses. Copyright © 2012 John Wiley &amp; Sons, Ltd.

Dynamics of Plains Cottonwood (Populus deltoides) Forests and Historical Landscape Change along Unchannelized Segments of the Missouri River, USA

Construction of six large dams and reservoirs on the Missouri River over the last 50-75years has resulted in major landscape changes and alterations in flow patterns, with implications for riparian forests dominated by plains cottonwood (Populus deltoides). We quantified changes in land cover from 1892-1950s and the 1950s-2006 and the current extent and age structure of cottonwood forests on seven segments (two reservoir and five remnant floodplain) comprising 1127km (53%) of the unchannelized upper two-thirds of the Missouri River. Riparian forest area declined by 49%; grassland 61%; shrubland 52%; and sandbar habitat 96%; while agricultural cropland increased six-fold and river/reservoir surface area doubled from 1892 to 2006. Net rates of erosion and accretion declined between the 1892-1950s and 1950s-2006 periods. Accretion exceeded erosion on remnant floodplain segments, resulting in declines in active channel width, particularly in 1950s-2006. Across all study segments in 2006, most cottonwood stands (67%) were >50years old, 22% were 25-50years old, and only 10% were <25years old. Among stands <50years old, the higher proportion of 25-50year old stands represents recruitment that accompanied initial post-dam channel narrowing; while declines in sandbar and shrubland area and the low proportion of stands <25years old suggest declines in geomorphic dynamism and limited recruitment under recent river management. Future conservation and restoration efforts should focus both on limiting further loss of remnant cottonwood stands and developing approaches to restore river dynamics and cottonwood recruitment processes.

Changes in the sublingual microcirculation and endothelial adhesion molecules during the course of severe meningococcal disease treated in the paediatric intensive care unit

The sublingual microcirculation can be visualised in real time using sidestream dark-field (SDF) imaging. Endothelial activation mediated through adhesion molecules may alter flow patterns in the microcirculation. We studied sublingual microcirculatory disturbances in children with meningococcal disease (MCD) and simultaneously measured plasma levels of adhesion molecules. Twenty children admitted to the paediatric intensive care unit (PICU) with MCD were studied. Forty healthy children were controls. The sublingual microcirculation was assessed at admission and at timed intervals until extubation. The microvascular flow index (MFI), capillary density (CD), proportion of perfused vessels (PPV) and perfused vessel density (PVD) were measured using SDF imaging. Plasma intercellular adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule-1 (VCAM-1), E-selectin and P-selectin were measured at admission and at timed intervals during the course of PICU treatment. Significant reductions in MFI, CD, PPV and PVD were found in children with MCD compared with controls (p<0.005). These differences had resolved prior to extubation. Initial MFI values predicted the duration of mechanical ventilation, irrespective of the stage of illness at the time of presentation to PICU. There were negative correlations between the ICAM-1, VCAM-1 and E-selectin levels and the microcirculatory MFI and PPV values at the time of admission to PICU (p<0.005). Microcirculatory dysfunction is present in children with severe MCD with improvement alongside clinical recovery. Microcirculatory dysfunction correlated with markers of endothelial activation. Sublingual SDF imaging is feasible in children ventilated on PICU for severe sepsis and may prove useful in studies assessing illness severity and therapy.

Arterial spin labeling and altered cerebral blood flow patterns in the minimally conscious state

To use arterial spin labeling (ASL) to compare cerebral blood flow (CBF) patterns in minimally conscious state (MCS) patients with those in normal controls in an observational study design. Subjects meeting MCS criteria and normal controls were identified. A pseudocontinuous ASL sequence was performed with subjects and controls in the resting awake state. Multiple CBF values for 10 predetermined regions of interest were sampled and average CBF was calculated and compared between controls and subjects. Ten normal controls were identified, with ages ranging from 26 to 54 years. Four subjects met the MCS criteria and received an ASL study, with one patient receiving a second study at a later date. Subjects ranged in age from 19 to 58 years and had traumatic brain injury, stroke, or hypoxic-ischemic encephalopathy. Regional CBF for controls ranged from 21.6 to 57.2 mL/100 g/min, with a pattern of relatively increased blood flow posteriorly including the posterior cingulate, parietal, and occipital cortices. CBF patterns for MCS subjects showed greater variability (from 7.7 to 33.1 mL/100 g/min), demonstrating globally decreased CBF in gray matter compared with that in normal controls, especially in the medial prefrontal and midfrontal regions. In the one subject studied longitudinally, global CBF values increased over time, which correlated with clinical improvement. We identified globally decreased CBF and a selective reduction of CBF within the medial prefrontal and midfrontal cortical regions as well as gray matter in MCS patients. ASL may serve as an adjunctive method to assess functional reserve in patients recovering from severe brain injuries.

GROUNDWATER INFLUENCES ON THE DISTRIBUTION AND ABUNDANCE OF RIVERINE SMALLMOUTH BASS, MICROPTERUS DOLOMIEU, IN PASTURE LANDSCAPES OF THE MIDWESTERN USA

ABSTRACTThis study examined how spring‐flow (SF) contributions to streams related to the distribution and abundance of smallmouth bass Micropterus dolomieu in a predominately pasture landscape in Missouri, USA. Stream segments (N = 13) with similar landscape characters were classified by SF volume into high SF (HSF) or low SF (LSF) groups. The densities of smallmouth bass, channel unit (CU) use and temperature‐selection patterns were assessed for several life stages and frequency distributions for age 0 fish. More smallmouth bass were present in stream segments with HSF influence. Age 0 fish were twice as likely to be present in HSF stream segments. Older age classes were present in stream reaches independent of SF contribution. For all age classes, the use of particular CUs did not depend on SF influence. All age classes were more likely to be present in pools than other CUs. Microhabitat temperature selection differed among age classes. Age 0 fish selected warmer temperatures with a gradual shift towards cooler temperatures for older age classes. The length frequency of age 0 fish was skewed towards larger individuals in streams with limited SF influence, whereas the length frequency in HSF stream segments was skewed towards smaller individuals. The benefits of significant groundwater via SF influence seem to be related to increased hatch or survival of age 0 fish and the availability of optimal temperatures for adult smallmouth bass growth. Thermal refugia and stable flows provided by springs should be recognised for their biological potential to provide suitable habitat as climate change and other land‐use alterations increase temperature regimes and alter flow patterns. Published in 2011 by John Wiley &amp; Sons, Ltd.

How to choose the best available homograft to reconstruct the right ventricular outflow tract

How to choose the best available homograft to reconstruct the right ventricular outflow tract

4D-MR flow analysis in patients after repair for tetralogy of Fallot

Comprehensive analysis of haemodynamics by 3D flow visualisation and retrospective flow quantification in patients after repair of tetralogy of Fallot (TOF). Time-resolved flow-sensitive 4D MRI (spatial resolution ~ 2.5 mm, temporal resolution = 38.4 ms) was acquired in ten patients after repair of TOF and in four healthy controls. Data analysis included the evaluation of haemodynamics in the aorta, the pulmonary trunk (TP) and left (lPA) and right (rPA) pulmonary arteries by 3D blood flow visualisation using particle traces, and quantitative measurements of flow velocity. 3D visualisation of whole heart haemodynamics provided a comprehensive overview on flow pattern changes in TOF patients, mainly alterations in flow velocity, retrograde flow and pathological vortices. There was consistently higher blood flow in the rPA of the patients (rPA/lPA flow ratio: 2.6 ± 2.5 vs. 1.1 ± 0.1 in controls). Systolic peak velocity in the TP was higher in patients (1.9 m/s ± 0.7 m/s) than controls (0.9 m/s ± 0.1 m/s). 4D flow-sensitive MRI permits the comprehensive evaluation of blood flow characteristics in patients after repair of TOF. Altered flow patterns for different surgical techniques in the small patient cohort may indicate its value for patient monitoring and potentially identifying optimal surgical strategies.

Intrahepatic vascular shunts: Strategy for early diagnosis, evaluation and management

PurposeTo propose a strategy for early diagnosis and management of intrahepatic vascular shunts (IHVSs). Patients and MethodsWe systematically screened 3143 patients liable to develop IHVSs. Diagnosed patients were comprehensively evaluated using color Doppler and multiphasic CT. Our management strategy based on imaging and clinical findings and categorized patients into three groups with different lines of management and we assessed the degree of shunt occlusion and clinical outcome. ResultsIHVSs were diagnosed in 134 patients. Two types of shunts were identified; arteriovenous (72%) and venovenous (28%). Small simple shunts (32%) showed no morphological or hemodynamic changes. Small complex shunts (57%) showed mild alterations in Doppler spectra. Large and aneurismal shunts (11%) showed increased diameters and flow velocities of the shunt vessels with alteration of flow pattern. By CT the vessels opacified during the early arterial phases in arteriovenous, and during the portovenous phase in venovenous shunts. During management, group I included 42%; 38% were conservatively managed and 4% underwent TIPS. Group II included 57% who underwent successful embolization in 50%, and <80% reduction in 7% of patients who underwent surgery. Direct surgery was selected for 1% of patients. ConclusionUsing color Doppler ultrasonography complemented by multiphasic CT allowed early diagnosis and evaluation of IHVSs and selection of the suitable treatment. Our management strategy allowed practical therapeutic implications and yielded good results.

Altered cerebral blood flow patterns associated with pathologic worry in the elderly

Generalized anxiety disorder (GAD) is the most prevalent anxiety disorder among the elderly and has high functional and cognitive morbidity. However, late-life GAD is relatively understudied and its functional neuroanatomy is uncharted. Several imaging studies have suggested abnormalities in the cognitive control systems of emotion regulation in anxiety disorders in young adults. The aim of this study was to examine the neural correlates of emotion regulation in late-life GAD. We compared 7 elderly GAD subjects and 10 elderly nonanxious comparison subjects using functional MRI. Regional cerebral blood flow (rCBF) was measured using pulsed arterial spin labeling perfusion MRI at rest and during an emotion regulation paradigm. Relative to the rest condition, elderly nonanxious comparison subjects had increased rCBF during worry induction (WI) in the right insula, bilateral amygdala, and associative temporooccipital areas. Elderly GAD subjects had increased rCBF during WI in the associative temporooccipital areas, but not in the insula or the amygdala. During worry suppression (WS), elderly nonanxious comparison subjects had increased rCBF in the prefrontal cortex (PFC) and dorsal ACC. Elderly GAD subjects had no changes in rCBF during WS in the PFC. When attempting to regulate their emotional responses, elderly anxious subjects failed to activate prefrontal regions involved in the downregulation of negative emotions. These results, showing that elderly anxious subjects are not effectively engaging the PFC in suppressing worry, may be clinically relevant for developing personalized therapeutic strategies for the treatment of late-life GAD.

In vivo three‐dimensional MR wall shear stress estimation in ascending aortic dilatation

To estimate surface-based wall shear stress (WSS) and evaluate flow patterns in ascending aortic dilatation (AscAD) using a high-resolution, time-resolved, three-dimensional (3D), three-directional velocity encoded, radially undersampled phase contrast MR sequence (4D PC-MRI). 4D PC-MRI was performed in 11 patients with AscAD (46.3 ± 22.0 years) and 10 healthy volunteers (32.9 ± 13.4 years) after written informed consent and institutional review board approval. Following manual vessel wall segmentation of the ascending aorta (MATLAB, The Mathworks, Natick, MA), a 3D surface was created using spline interpolation. Spatial WSS variation based on surface division in 12 segments and temporal variation were evaluated in AscAD and normal aortas. Visual analysis of flow patterns was performed based on streamlines and particle traces using EnSight (v9.0, CEI, Apex, NC). AscAD was associated with significantly increased diastolic WSS, decreased systolic to diastolic WSS ratio, and delayed onset of peak WSS (all P < 0.001). Temporally averaged WSS was increased and peak systolic WSS was decreased. The maximum WSS in AscAD was on the anterior wall of the ascending aorta. Vortical flow with highest velocities along the anterior wall and increased helical flow during diastole were observed in AscAD compared with controls. Changes in WSS in the ascending aorta of AscAD correspond to observed alterations in flow patterns compared to controls.

Fluid Simulation of a Transcatheter Aortic Valve Deployment into a Patient-Specific Aortic Root

Successful transcatheter aortic valve (TAV) deployment and function are heavily reliant on the implant-host tissue interaction. Many adverse events observed clinically in TAV procedures such as impairment of coronary artery flow, paravalvular leak, and access site injury could be attributed to improper TAV deployment and interaction with the aortic root. In this study, we performed a computational analysis of the TAV-aortic root interaction, particularly the hemodynamics before and after TAV deployment. Utilizing a recently developed computational TAV model, we simulated the deployment of this TAV into a 68 year old male patient. The geometry of the patient’s aortic valve and root were extracted from clinical CT images. From the simulation results, we obtained a peak transvalvular pressure drop of 78.45 and 25.27 mmHg before and after the TAV deployment, respectively. The mean systolic ejection transvalvular pressure reduced from 45.8 to 7.55 mmHg and effective orifice area (EOA) increased from 0.53 to 1.595 cm2 following the TAV intervention. The altered flow pattern following TAV intervention resulted in a significant pressure drop in the vicinity of the sinuses of Valsalva, and a corresponding decrease in percentage of cardiac output reaching the coronary arteries from 5.14 to 4.07% from pre- to post-TAV deployment. In conclusion, the developed computational models allow for a quantitative analysis of the hemodynamics before and after TAV intervention, and thus could be an enabling tool for patient screening and TAV design improvement.