Computation of Hemodynamics in Tortuous Left Coronary Artery: A Morphological Parametric Study

Tortuosity of the left anterior descending artery is associated with hypertension and is not independently related to physical performance: A cardiac computed tomography study

BACKGROUND

Coronary tortuosity (CorT) is frequently observed in invasive angiography, though its aetiology and clinical significance remain ambiguous. Prior research has indicated possible links between CorT and factors such as hypertension, age, and calcium scores in the left anterior descending (LAD) artery. The aim of this study was to examine and optimize the usage of coronary computed tomography angiography (CCTA) with vessel tracking to explore these associations.

METHODS

Observational sub-study of the single centre randomised controlled CATCH-trial. From the original study 600 participants, who underwent CCTA, 250 were randomly selected. Clinical data and patient risk factors were sourced from medical records and structured interviews. Tortuosity of the LAD was quantified by calculating the ratio of the actual vessel-length to the straight-line distance.

RESULTS

The final study population comprised 194 patients (56 patients were excluded due to poor image quality or inability to perform adequate vessel tracking). After adjusting for confounding variables, tortuosity was significantly associated with hypertension (p < 0.001), female gender (p = 0.01), and increasing age (p = 0.045). No significant correlation was observed between CorT and calcium scores. Univariate analysis indicated that higher CorT levels were linked to lower metabolic equivalents of task (METs) in bicycle tests (p = 0.003); however, this relationship became nonsignificant (p = 0.97) upon adjustment for age, gender, and hypertension.

CONCLUSIONS

Our findings suggest that increased CorT is most prevalent in patients with hypertension, advancing age, and female gender. Although higher tortuosity levels did not significantly impact METs during physical activity, further research is warranted to explore the underlying mechanisms of this relationship.

A new understanding of coronary curvature and haemodynamic impact on the course of plaque onset and progression

The strong link between atherosclerosis and luminal biomechanical stresses is well established. Yet, this understanding has not translated into preventative coronary diagnostic imaging, particularly due to the under-explored role of coronary anatomy and haemodynamics in plaque onset, which we aim to address with this work. The left coronary trees of 20 non-stenosed (%diameter stenosis [%DS] = 0), 12 moderately (0 < %DS < 70) and 7 severely (%DS ≥ 70) stenosed cases were dissected into bifurcating and non-bifurcating segments for whole-tree and segment-specific comparisons, correlating nine three-dimensional coronary anatomical features, topological shear variation index (TSVI) and luminal areas subject to low time-average endothelial shear stress (%LowTAESS), high oscillatory shear index (%HighOSI) and high relative residence time (%HighRRT). We found that TSVI is the only metric consistently differing between non-stenosed and stenosed cases across the whole tree, bifurcating and non-bifurcating segments (p < 0.002, AUC = 0.876), whereas average curvature and %HighOSI differed only for the whole trees (p < 0.024) and non-bifurcating segments (p < 0.027), with AUC > 0.711. Coronary trees with moderate or severe stenoses differed only in %LowTAESS (p = 0.009) and %HighRRT (p = 0.012). This suggests TSVI, curvature and %HighOSI are potential factors driving plaque onset, with greater predictive performance than the previously recognized %LowTAESS and %HighRRT, which appears to play a role in plaque progression.

Patient-Specific Numerical Simulations of Coronary Artery Hemodynamics and Biomechanics: A Pathway to Clinical Use

PURPOSE

Numerical models that simulate the behaviors of the coronary arteries have been greatly improved by the addition of fluid-structure interaction (FSI) methods. Although computationally demanding, FSI models account for the movement of the arterial wall and more adequately describe the biomechanical conditions at and within the arterial wall. This offers greater physiological relevance over Computational Fluid Dynamics (CFD) models, which assume the walls do not move or deform. Numerical simulations of patient-specific cases have been greatly bolstered by the use of imaging modalities such as Computed Tomography Angiography (CTA), Magnetic Resonance Imaging (MRI), Optical Coherence Tomography (OCT), and Intravascular Ultrasound (IVUS) to reconstruct accurate 2D and 3D representations of artery geometries. The goal of this study was to conduct a comprehensive review on CFD and FSI models on coronary arteries, and evaluate their translational potential.

METHODS

This paper reviewed recent work on patient-specific numerical simulations of coronary arteries that describe the biomechanical conditions associated with atherosclerosis using CFD and FSI models. Imaging modality for geometry collection and clinical applications were also discussed.

RESULTS

Numerical models using CFD and FSI approaches are commonly used to study biomechanics within the vasculature. At high temporal and spatial resolution (compared to most cardiac imaging modalities), these numerical models can generate large amount of biomechanics data.

CONCLUSIONS

Physiologically relevant FSI models can more accurately describe atherosclerosis pathogenesis, and help to translate biomechanical assessment to clinical evaluation.

Multi-Dimensional Modeling of Cerebral Hemodynamics: A Systematic Review

The Circle of Willis (CoW) describes the arterial system in the human brain enabling the neurovascular blood supply. Neurovascular diseases like intracranial aneurysms (IAs) can occur within the CoW and carry the risk of rupture, which can lead to subarachnoid hemorrhage. The assessment of hemodynamic information in these pathologies is crucial for their understanding regarding detection, diagnosis and treatment. Multi-dimensional in silico approaches exist to evaluate these hemodynamics based on patient-specific input data. The approaches comprise low-scale (zero-dimensional, one-dimensional) and high-scale (three-dimensional) models as well as multi-scale coupled models. The input data can be derived from medical imaging, numerical models, literature-based assumptions or from measurements within healthy subjects. Thus, the most realistic description of neurovascular hemodynamics is still controversial. Within this systematic review, first, the models of the three scales (0D, 1D, 3D) and second, the multi-scale models, which are coupled versions of the three scales, were discussed. Current best practices in describing neurovascular hemodynamics most realistically and their clinical applicablility were elucidated. The performance of 3D simulation entails high computational expenses, which could be reduced by analyzing solely the region of interest in detail. Medical imaging to establish patient-specific boundary conditions is usually rare, and thus, lower dimensional models provide a realistic mimicking of the surrounding hemodynamics. Multi-scale coupling, however, is computationally expensive as well, especially when taking all dimensions into account. In conclusion, the 0D-1D-3D multi-scale approach provides the most realistic outcome; nevertheless, it is least applicable. A 1D-3D multi-scale model can be considered regarding a beneficial trade-off between realistic results and applicable performance.

Treatment of Highly Angulated Lesions Using SuperCross Microcatheter

Unusually angulated coronary anatomy can decrease the success rate of coronary interventions by hindering successful wiring and equipment delivery. Additionally, due to the technical challenges involved, there is increased risk for complications such as perforations, dissections, stent loss, and equipment entrapment. In this case series, we illustrate the advantages of using angulated microcatheters to facilitate successful treatment of such patients in various clinical scenarios.

Coronary Tortuosity as a New Phenotype for Ischemia without Coronary Artery Disease

BACKGROUND

Coronary arteries tend to be more tortuous than other arteries and follow the repeated flexion and relaxation movements that occur during the cardiac cycle. Coronary tortuosity (CorT) leads to changes in coronary flow with a reduction in distal perfusion pressure, which could cause myocardial ischemia.

OBJECTIVE

To assess the association between CorT and myocardial ischemia.

METHODS

Between January 2015 and December 2017, 57 patients with angina and nonobstructive coronary artery disease detected by invasive coronary angiography (ICA) were retrospectively enrolled. Angiographic variables were analyzed to assess the presence and degree of tortuosity and correlated with their respective vascular territories on stress myocardial perfusion imaging (MPI). CorT was defined as coronary arteries with three or more bend angles ≤90°, measured during diastole. Statistical significance was determined at the 5% level.

RESULTS

A total of 17 men and 40 women were enrolled (mean age 58.3 years). CorT was observed in 16 patients (28%) and in 24 of 171 arteries. There was a significant association between CorT and ischemia when analyzed per artery (p<0.0001). The angiographic factor most associated with ischemia was the number of bend angles in an epicardial artery measured at systole (p=0.021).

CONCLUSION

This study showed an association of CorT and myocardial ischemia in patients with unobstructed coronary arteries and angina. An increased number of coronary bend angles measured by angiography during systole was related to ischemia.

Subarachnoid Hemorrhage from Ruptured Internal Carotid Artery Aneurysm: Association with Arterial Tortuosity

OBJECTIVE

Many researchers have found a correlation between tortuous arteries and development of aneurysms in cerebral arteries. We decided to determine whether tortuosity of the internal carotid artery can be related to its aneurysm rupture.

METHODS

We retrospectively analyzed the internal carotid artery anatomy of 149 patients with internal carotid artery aneurysms. For each patient, we calculated relative length (RL), sum of angle metrics (SOAM), triangular index (TI), product of angle distance (PAD), and inflection count metrics (ICM).

RESULTS

A total of 33 patients (22.15%) had subarachnoid hemorrhage. These patients had significantly lower SOAM (0.31 ± 0.17 vs. 0.42 ± 0.21; P < 0.01), TI (0.27 ± 0.09 vs. 0.31 ± 0.11; P = 0.03) and ICM (0.25 ± 0.11 vs. 0.31 ± 0.17; P = 0.04). In multivariate logistic regression analysis, higher SOAM (odds ratio, 0.780; 95% confidence interval, 0.619-0.961; P = 0.025) remained independently associated with lower risk of internal carotid artery aneurysm rupture. In addition, we found significant positive correlation of aneurysm dome size with SOAM (R = 0.224; P = 0.013) and PAD (0.269; P < 0.01). Our study also showed that age (R = 0.252; P = 0.036), Glasgow Coma Scale score (R = -0.706; P < 0.01), and TI (R = -0.249; P = 0.042) were independently correlated with modified Rankin Scale score on discharge.

CONCLUSIONS

Lower tortuosity might be a protective factor against internal carotid artery aneurysm rupture and poor outcome after subarachnoid hemorrhage. Higher tortuosity is correlated with internal carotid artery aneurysm growth.

Impact of Coronary Artery Tortuosity on Outcomes Following Stenting: A Pooled Analysis From 6 Trials

OBJECTIVES

The authors sought to determine whether coronary artery tortuosity negatively affects clinical outcomes after stent implantation.

BACKGROUND

Coronary artery tortuosity is a common angiographic finding and has been associated with increased rates of early and late major adverse events after balloon angioplasty.

METHODS

Individual patient data from 6 prospective, randomized stent trials were pooled. Outcomes at 30 days and 5 years following percutaneous coronary intervention of a single coronary lesion were analyzed according to the presence or absence of moderate/severe vessel tortuosity, as determined by an angiographic core laboratory. The primary endpoint was target vessel failure (TVF) (composite of cardiac death, target vessel-related myocardial infarction [TV-MI], or ischemia-driven target vessel revascularization [ID-TVR]).

RESULTS

A total of 6,951 patients were included, 729 of whom (10.5%) underwent percutaneous coronary intervention in vessels with moderate/severe tortuosity. At 30 days, TVF was more frequent in patients with versus without moderate/severe tortuosity (3.8% vs. 2.4%; hazard ratio [HR]: 1.64; 95% confidence interval [CI]: 1.09 to 2.46; p = 0.02), a difference driven by a higher rate of TV-MI. At 5 years, TVF remained increased in patients with moderate/severe tortuosity (p = 0.003), driven by higher rates of TV-MI (p = 0.003) and ID-TVR (p = 0.01). Definite stent thrombosis was also greater in patients with versus without moderate/severe tortuosity (1.9% vs. 1.0%; HR: 1.86; 95% CI: 1.02 to 3.39; p = 0.04). After adjustment for baseline covariates, moderate/severe vessel tortuosity was independently associated with TV-MI and ID-TVR at 5 years (p = 0.04 for both).

CONCLUSIONS

Stent implantation in vessels with moderate/severe coronary artery tortuosity is associated with increased rates of TVF due to greater rates of TV-MI and ID-TVR.

Coronary flow reserve and microcirculatory resistance in patients with coronary tortuosity and without atherosclerosis

Objective

Coronary tortuosity may affect epicardial coronary arterial blood flow. This study aimed to investigate the effect of coronary tortuosity on coronary flow reserve and the coronary microcirculation in patients without apparent coronary atherosclerosis.

Methods

Prospective patients (n = 8, 3 men, mean age: 58 ± 6.0 years) with coronary tortuosity and without apparent coronary atherosclerosis were enrolled. Coronary tortuosity was defined by the finding of ≥three bends (defined as a ≥45° change in vessel direction) along the main trunk of the left anterior descending artery or left circumflex artery. Coronary flow reserve and the index of microcirculatory resistance were measured by the thermodilution technique.

Results

A total of eight coronary arteries with coronary tortuosity were analyzed. The mean fractional flow reserve was 0.98 ± 0.007. The mean coronary flow reserve was 1.5 ± 0.3, which is much lower than that in the normal coronary artery as reported in the literature. The mean index of microcirculatory resistance was 26.7 ± 2.3, which is much higher than that in the normal coronary artery.

Conclusions

Coronary tortuosity is associated with decreased coronary flow reserve and an increased index of microcirculatory resistance.

Trial registration: This study is registered at the Chinese Clinical Trial Registry, NCT No: ChiCTR2000033671

Effect of arterial curvature on hemodynamics and mass transport

BACKGROUND

Atherosclerotic lesions develop preferentially at certain sites in the human arterial system, such as the inner wall of curved segments and the outer wall of bifurcations. Local wall shear stress (WSS) and concentration of low density lipoprotein (LDL) have been identified as two important factors contributing to these lesions.

OBJECTIVE

To determine if a connection exists between arterial curvature and the formation of atherosclerosis.

METHODS

A set of 3-D vessel models with different bend angles was constructed. By comparing blood flow, WSS, and LDL aggregation, the influence of bend curvature on atherosclerotic lesions was assessed.

RESULTS

Upon increasing arterial bending, low WSS regions were formed at the outer wall of the junction between straight and curved segments, as well as the inner wall of curved segments. However, high LDL concentrations only appeared at the inner wall of the bend region. A connection between secondary flow and LDL concentration was observed; high LDL concentration regions had stronger secondary flow. Higher water infiltration velocity could enhance LDL aggregation, while blood non-Newtonian properties, by easing secondary flow, diminished its aggregation.

CONCLUSIONS

Under the same flow rate, a larger bend angle increased flow resistance, lowered WSS, and increased LDL surface concentrations, thus indicating an increased risk of atherosclerosis.

Increased tortuosity of ACA might be associated with increased risk of ACoA aneurysm development and less aneurysm dome size: a computer-aided analysis

Objectives

We decided to perform computer-aided analysis of the anterior cerebral artery (ACA) to check for a potential correlation with anterior communicating artery (ACoA) aneurysm presence and growth.

Methods

We retrospectively analyzed the ACA anatomy of 121 patients with ACoA aneurysms along with 121 age, risk factors, and vessel side-matched control patients without an ACoA aneurysm. We obtained their medical history and digital subtraction angiography (DSA) data from their medical records. For each patient’s DSA, we extracted curve representing the course of their ACA and calculated its relative length (RL), sum of angle metrics (SOAM), triangular index (TI), product of angle distance (PAD), and inflection count metrics (ICM).

Results

Patients with ACoA aneurysm had significantly higher RL (0.64 ± 0.23 vs. 0.56 ± 0.22; p < 0.01), SOAM (0.27 ± 0.19 vs. 0.18 ± 0.15; p < 0.01), PAD (0.12 ± 0.13 vs. 0.09 ± 0.11; p = 0.02), and TI (0.57 ± 0.14 vs. 0.44 ± 0.15; p < 0.01). In multivariate logistic regression analysis, after adjustment for possible confounders, SOAM (OR, 1.34; 95% CI, 1.12–1.63; p < 0.01) and TI (OR, 1.84; 95% CI, 1.47–2.35; p < 0.01) remained independently associated with higher risk of ACoA aneurysm. Additionally, we found significant negative correlations between TI and aneurysm dome size (R = − 0.194; p = 0.047).

Conclusions

Increased tortuosity of ACA might increase the risk of ACoA aneurysm development and decrease the risk of aneurysm growth.

Key Points

• Anterior cerebral artery’s sum of angle metrics is associated with hypertension as well as with history of ischemic stroke and myocardial infarction.

• Increased tortuosity of anterior cerebral artery might be associated with anterior communicating artery aneurysm development.

• Tortuosity of anterior cerebral artery is negatively correlated with anterior communicating artery aneurysm dome size.

Analysis of Anterior Cerebral Artery Tortuosity: Association with Anterior Communicating Artery Aneurysm Rupture

BACKGROUND

Many researchers have found a correlation between tortuous arteries and development of aneurysms in cerebral arteries. However, there are no studies analyzing the impact of tortuosity on risk of subarachnoid hemorrhage (SAH) occurrence. Therefore, we decided to determine whether tortuosity of the anterior cerebral artery can be related to the rupture of anterior communicating artery aneurysm and to severity and treatment outcome of SAH.

METHODS

We retrospectively analyzed anterior cerebral artery anatomy of 121 patients with anterior communicating artery aneurysms. From patients' medical records, we obtained their history including previous and current diseases and medications. For each patient we calculated relative length, sum of angle metrics, triangular index, product of angle distance, and inflection count metrics.

RESULTS

Patients with SAH had significantly higher relative length (0.70 ± 0.19 vs. 0.63 ± 0.22; P = 0.03) and significantly lower inflection count metrics (0.10 ± 0.08 vs. 0.16 ± 0.19; P < 0.01), respectively. In multivariate logistic regression analysis, after adjustment of all possible confounders, diabetes mellitus (odds ratio [OR], 0.154; 95% confidence interval [CI], 0.032-0.553; P < 0.01) and higher inflection count metrics (OR, 0.604; 95% CI, 0.357-0.909; P = 0.042) remained independently associated with lower risk of SAH. We also found an independent correlation between aneurysm dome size (R = -0.289; P = 0.02) and triangular index (R = 0.273; P = 0.03) and Glasgow Coma Scale score on admission.

CONCLUSIONS

Higher anterior cerebral artery tortuosity might be a protective factor against anterior communicating artery aneurysm rupture.

Coronary tortuosity is negatively correlated with coronary atherosclerosis

Objective

The impact of coronary tortuosity on coronary atherosclerosis remains unclear. This study was performed to determine to the relationship between coronary tortuosity and the presence of coronary atherosclerosis.

Methods

Tortuosity and the presence of coronary atherosclerosis in the main coronary arteries were evaluated. The coronary artery was divided into non-tortuous and tortuous segments. The incidence of coronary atherosclerosis between the two segments was compared.

Results

The prevalence of coronary atherosclerotic stenosis was significantly lower in the tortuous than non-tortuous segment.

Conclusion

The prevalence of coronary atherosclerotic stenosis is lower in the coronary tortuous than non-tortuous segment, indicating that coronary tortuosity might be considered a protective factor for atherosclerosis.

Computational estimation of the hemodynamic significance of coronary stenoses in arterial branches deriving from CCTA: A proof-of-concept study

The development of non-invasive methods for the accurate hemodynamic assessment of the coronary vasculature has become a non-trivial matter for the everyday clinical practice. Virtual Functional Assessment Index has already been suggested as a valid alternative to the invasively measured FFR but only on coronary arterial segments. In this work, we propose a novel method for the estimation of the severity of coronary lesions in arterial branches from CCTA derived images. Four left arterial branches were reconstructed in 3D using our in-house developed 3D reconstruction algorithm, and were subjected to computational blood flow simulations for the final calculation of the vFAI through the whole arterial branch. Strong correlation was found (r=0.82) between the two methods. A small relative error of 3.2% and a small trend of overestimation (0.023, SD=0.088) were also observed. All pathological cases presenting ischemia, were correctly discriminated by our method as hemodynamically significant lesions.

Vascular Remodelling Relates to an Elevated Oscillatory Shear Index and Relative Residence Time in Spontaneously Hypertensive Rats

Haemodynamic disorders are common clinical findings in hypertension and lead to adverse cardiovascular events. However, the haemodynamic conditions in hypertension models are poorly understood. This study aimed to observe the characteristics of haemodynamics in spontaneously hypertensive rats (SHRs) and antihypertensive-treated SHRs. Twenty-four adult male SHRs and Wistar-Kyoto rats (WKYs) were randomly divided into four groups and treated for 7 days as follows: WKY-CON (WKYs + saline), WKY-NIF (WKYs + nifedipine, 50 mg/kg/day), SHR-CON (SHRs + saline), and SHR-NIF (SHRs + nifedipine). Aortic computational fluid dynamics (CFD) models were simulated to obtain the haemodynamic parameters. We found that in the hypertensive (SHR-CON) and blood pressure-controlled (SHR-NIF) groups, the oscillatory shear index (OSI) and relative residence time (RRT), which are key haemodynamics indices, were markedly elevated. Furthermore, there was a correlation between both the elevated OSI and RRT with the vascular wall thickening in regions near the inner wall of the aortic arch. Our research demonstrates that haemodynamics remains disturbed even if the blood pressure is normalized. In addition, vascular remodelling may play an important role in maintaining elevated OSI and RRT values.

Computational estimation of the severity of coronary lesions with intravascular ultrasound images: a pilot study

The fast and accurate hemodynamic functional assessment of the coronary vasculature is of utmost importance in clinical practice due to the fact that Cardiovascular Diseases have become the leading cause of death globally. In this work we propose a novel method that combines two of the most efficient methods of hemodynamic status assessment of coronary arteries, Intravascular UtraSound and virtual Functional Assessment Index, an index that correlates well to the measured Fractional Flow Reserve. One Left Anterior Descending segment was reconstructed both in a straight manner (using only IVUS images) as well as using the actual 3D geometry of the vessel (using IvUS images combined with the respective coronary angiographic images [2]). The generated vFAI values were almost identical (Straight=0.80, 3D=0.79), presenting a relative error of 1.27%, thus proving the efficacy of the proposed method. We also calculated the Endothelial Shear Stress for the two models under rest (i.e. flow rate of 1 ml/s), observing a similar trend throughout the artery, but with a statistically important relative error of 13.49%, as expected.

DIRECT CORONARY COUPLING APPROACH FOR COMPUTING FFRCT

With the advances in computational fluid dynamics (CFD) and image-based modeling techniques, fractional flow reserve (FFR) can be computed from coronary computed tomography angiography (CTA) scans (FFRCT). However, this non-invasive approach requires large-scale computational resources, which limits its application in routine clinical setting. A 3D–0D coupling approach is proposed to improve the coupling efficiency of FFRCT. Aortic–root is modeled by a lumped parameter model and connected with the models of left ventricle and systemic circulation. With this approach, the interested coronary regions can be directly coupled to the lumped parameter model, resulting in a significant reduction (up to 20 times reduction) in the volume of the CFD computing domain. The proposed approach is applied to a patient-specific model and compared with previous non-reduced approach. Results show that the computed coronary flow rates, pressure waveforms and FFRCT contours by the proposed approach are consistent well with that of the non-reduced approach. These results demonstrate that the proposed approach can reduce the CFD computing domain of FFRCT significantly while maintaining the similar accuracy as compared with the non-reduced approach, and it can be further employed to promote FFRCT in routine clinical setting.

Numerical analysis of the effect of turbulence transition on the hemodynamic parameters in human coronary arteries

BACKGROUND

Local hemodynamics plays an important role in atherogenesis and the progression of coronary atherosclerosis disease (CAD). The primary biological effect due to blood turbulence is the change in wall shear stress (WSS) on the endothelial cell membrane, while the local oscillatory nature of the blood flow affects the physiological changes in the coronary artery. In coronary arteries, the blood flow Reynolds number ranges from few tens to several hundreds and hence it is generally assumed to be laminar while calculating the WSS calculations. However, the pulsatile blood flow through coronary arteries under stenotic condition could result in transition from laminar to turbulent flow condition.

METHODS

In the present work, the onset of turbulent transition during pulsatile flow through coronary arteries for varying degree of stenosis (i.e., 0%, 30%, 50% and 70%) is quantitatively analyzed by calculating the turbulent parameters distal to the stenosis. Also, the effect of turbulence transition on hemodynamic parameters such as WSS and oscillatory shear index (OSI) for varying degree of stenosis is quantified. The validated transitional shear stress transport (SST) k-ω model used in the present investigation is the best suited Reynolds averaged Navier-Stokes turbulence model to capture the turbulent transition. The arterial wall is assumed to be rigid and the dynamic curvature effect due to myocardial contraction on the blood flow has been neglected.

RESULTS

Our observations shows that for stenosis 50% and above, the WSSavg, WSSmax and OSI calculated using turbulence model deviates from laminar by more than 10% and the flow disturbances seems to significantly increase only after 70% stenosis. Our model shows reliability and completely validated.

CONCLUSIONS

Blood flow through stenosed coronary arteries seems to be turbulent in nature for area stenosis above 70% and the transition to turbulent flow begins from 50% stenosis.

Three-dimensional hemodynamics analysis of the circle of Willis in the patient-specific nonintegral arterial structures

The hemodynamic alteration in the cerebral circulation caused by the geometric variations in the cerebral circulation arterial network of the circle of Wills (CoW) can lead to fatal ischemic attacks in the brain. The geometric variations due to impairment in the arterial network result in incomplete cerebral arterial structure of CoW and inadequate blood supply to the brain. Therefore, it is of great importance to understand the hemodynamics of the CoW, for efficiently and precisely evaluating the status of blood supply to the brain. In this paper, three-dimensional computational fluid dynamics of the main CoW vasculature coupled with zero-dimensional lumped parameter model boundary condition for the CoW outflow boundaries is developed for analysis of the blood flow distribution in the incomplete CoW cerebral arterial structures. The geometric models in our study cover the arterial segments from the aorta to the cerebral arteries, which can allow us to take into account the innate patient-specific resistance of the arterial trees. Numerical simulations of the governing fluid mechanics are performed to determine the CoW arterial structural hemodynamics, for illustrating the redistribution of the blood flow in CoW due to the structural variations. We have evaluated our coupling methodology in five patient-specific cases that were diagnosed with the absence of efferent vessels or impairment in the connective arteries in their CoWs. The velocity profiles calculated by our approach in the segments of the patient-specific arterial structures are found to be very close to the Doppler ultrasound measurements. The accuracy and consistency of our hemodynamic results have been improved (to [Formula: see text] %) compared to that of the pure-resistance boundary conditions (of 43.5 [Formula: see text] 28 %). Based on our grouping of the five cases according to the occurrence of unilateral occlusion in vertebral arteries, the inter-comparison has shown that (i) the flow reduction in posterior cerebral arteries is the consequence of the unilateral vertebral arterial occlusion, and (ii) the flow rate in the anterior cerebral arteries is correlated with the posterior structural variations. This study shows that our coupling approach is capable of providing comprehensive information of the hemodynamic alterations in the pathological CoW arterial structures. The information generated by our methodology can enable evaluation of both the functional and structural status of the clinically significant symptoms, for assisting the treatment decision-making.

Effects of Vessel Tortuosity on Coronary Hemodynamics: An Idealized and Patient-Specific Computational Study

Although coronary tortuosity can influence the hemodynamics of coronary arteries, the relationship between tortuosity and flow has not been thoroughly investigated partly due to the absence of a widely accepted definition of tortuosity and the lack of patient-specific studies that analyze complete coronary trees. Using a computational approach we investigated the effects of tortuosity on coronary flow parameters including pressure drop, wall shear stress, and helical flow strength as measured by helicity intensity. Our analysis considered idealized and patient-specific geometries. Overall results indicate that perfusion pressure decreases with increased tortuosity, but the patient-specific results show that more tortuous vessels have higher physiological wall shear stress values. Differences between the idealized and patient-specific results reveal that an accurate representation of coronary tortuosity must account for all relevant geometric aspects, including curvature imposed by the heart shape. The patient-specific results exhibit a strong correlation between tortuosity and helicity intensity, and the corresponding helical flow contributes directly to the observed increase in wall shear stress. Therefore, helicity intensity may prove helpful in developing a universal parameter to describe tortuosity and assess its impact on patient health. Our data suggest that increased tortuosity could have a deleterious impact via a reduction in coronary perfusion pressure, but the attendant increase in wall shear stress could afford protection against atherosclerosis.

Effects of Sucroferric Oxyhydroxide Compared to Lanthanum Carbonate and Sevelamer Carbonate on Phosphate Homeostasis and Vascular Calcifications in a Rat Model of Chronic Kidney Failure

Elevated serum phosphorus, calcium, and fibroblast growth factor 23 (FGF23) levels are associated with cardiovascular disease in chronic renal disease. This study evaluated the effects of sucroferric oxyhydroxide (PA21), a new iron-based phosphate binder, versus lanthanum carbonate (La) and sevelamer carbonate (Se), on serum FGF23, phosphorus, calcium, and intact parathyroid hormone (iPTH) concentrations, and the development of vascular calcification in adenine-induced chronic renal failure (CRF) rats. After induction of CRF, renal function was significantly impaired in all groups: uremic rats developed severe hyperphosphatemia, and serum iPTH increased significantly. All uremic rats (except controls) then received phosphate binders for 4 weeks. Hyperphosphatemia and increased serum iPTH were controlled to a similar extent in all phosphate binder-treatment groups. Only sucroferric oxyhydroxide was associated with significantly decreased FGF23. Vascular calcifications of the thoracic aorta were decreased by all three phosphate binders. Calcifications were better prevented at the superior part of the thoracic and abdominal aorta in the PA21 treated rats. In adenine-induced CRF rats, sucroferric oxyhydroxide was as effective as La and Se in controlling hyperphosphatemia, secondary hyperparathyroidism, and vascular calcifications. The role of FGF23 in calcification remains to be confirmed.

Effects of severity and location of stenosis on the hemodynamics in human aorta and its branches

Pulsatile blood flow is studied in a three-dimensional model of human thoracic aorta at different stages of atherosclerotic lesion growth, taking into account the effect of atherosclerotic plaque location and peripheral symmetry. The model is reconstructed from the computed tomography images. The wall shear stress (WSS), time-averaged WSS, and the oscillatory shear index are applied to determine susceptible sites for the onset of early atherosclerosis. Then, two different degrees of stenosis severity, 50 and 80 %, are introduced to vulnerable areas of the healthy aorta geometry. The overriding issue addressed is that the WSS distribution and magnitude are strongly affected by the atherosclerotic plaque size, its symmetric features, and the location, i.e., the branch it is formed. The present study, for the first time, is capable of providing information on the high shear environment that may exist upon the rupture of plaque surface and any thrombosis due to platelet deposition. The magnitude of WSS and its distribution at the throat of 50 % stenosed aortic arch are in agreement with the previous numerical study (Huang et al. in Exp Fluids 48(3):497-508, 2010). Results show that WSS values exceed 50 Pa at the throat of 80 % stenosed left common carotid and brachiocephalic arteries.