Haemodynamic analysis of femoral artery bifurcation models under different physiological flow waveforms

Structural and Mechanical Properties of Human Superficial Femoral and Popliteal Arteries

The femoropopliteal artery (FPA) is the main artery in the lower limb. It supplies blood to the leg muscles and undergoes complex deformations during limb flexion. Atherosclerotic disease of the FPA (peripheral arterial disease, PAD) is a major public health burden, and despite advances in surgical and interventional therapies, the clinical outcomes of PAD repairs continue to be suboptimal, particularly in challenging calcified lesions and biomechanically active locations. A better understanding of human FPA mechanical and structural characteristics in relation to age, risk factors, and the severity of vascular disease can help develop more effective and longer-lasting treatments through computational modeling and device optimization. This review aims to summarize recent research on the main biomechanical and structural properties of human superficial femoral and popliteal arteries that comprise the FPA and describe their anatomy, composition, and mechanical behavior under different conditions.

Computational Fluid Dynamics for the Prediction of Endograft Thrombosis in the Superficial Femoral Artery

Purpose:

Contemporary diagnostic modalities, including contrast-enhanced computed tomography (CTA) and duplex ultrasound, have been insufficiently able to predict endograft thrombosis. This study introduces an implementation of image-based computational fluid dynamics (CFD), by exemplification with 4 patients treated with an endograft for occlusive disease of the superficial femoral artery (SFA). The potential of personalized CFD for predicting endograft thrombosis is investigated.

Materials and Methods:

Four patients treated with endografts for an occluded SFA were retrospectively included. CFD simulations, based on CTA and duplex ultrasound, were compared for patients with and without endograft thrombosis to investigate potential flow-related causes of endograft thrombosis. Time-averaged wall shear stress (TAWSS) was computed, which highlights areas of prolonged residence times of coagulation factors in the graft.

Results:

CFD simulations demonstrated normal TAWSS (>0.4 Pa) in the SFA for cases 1 and 2, but low levels of TAWSS (<0.4 Pa) in cases 3 and 4, respectively. Primary patency was achieved in cases 1 and 2 for over 2 year follow-up. Cases 3 and 4 were complicated by recurrent endograft thrombosis.

Conclusion:

The presence of a low TAWSS was associated with recurrent endograft thrombosis in subjects with otherwise normal anatomic and ultrasound assessment and a good distal run-off.

Ultrasonographic Appearance of the Lower Extremity Arteries After Femoropopliteal Bypass Surgery

Objective:

The aim of this study was to assess the ultrasonographic appearance of the lower extremity arteries, after a femoropopliteal bypass surgery.

Materials and Methods:

Ninety patients, with atherosclerotic peripheral artery disease, underwent either autologous vein (30 subjects) or synthetic femoropopliteal bypass grafting, using an end-to-side (30 subjects) or end-to-end anastomotic technique. The outcomes were compared to 30 volunteers, who were recruited to serve as healthy controls. A lower extremity duplex ultrasonogram (DUS) was performed 1 year after treatment. The healthy volunteers underwent DUS at the point of being included in the study.

Results:

In healthy volunteers, the angle between the profunda femoris artery (deep femoral artery, PFA) and common femoral artery (CFA) did not exceed 30° of angulation. The diameter of the CFA, in the bifurcation area, was 9.8 ± 1.5 mm. The bypass patency rates, CFA diameter, PFA angle, and neointimal hyperplasia rates differed between the groups as presented.

Conclusion:

The results that were obtained may indicate the importance of bypass graft surveillance, using DUS, with precise analysis of the topography and geometry of the lower extremity arteries and vascular conduits, during the perioperative period. In addition, in this cohort, femoropopliteal bypass procedures were associated with an increase in the angle of the PFA from 30° to 80° of angulation. An increase in the diameter of the CFA in the area of the proximal anastomosis from 9.8 to 15.1 mm was also noted. In these patients, the saphenous vein bypasses were associated with minimal changes of the vascular geometry and better patency rates.

Computational Fluid Dynamics for the Prediction of Endograft Thrombosis in the Superficial Femoral Artery

PURPOSE

Contemporary diagnostic modalities, including contrast-enhanced computed tomography (CTA) and duplex ultrasound, have been insufficiently able to predict endograft thrombosis. This study introduces an implementation of image-based computational fluid dynamics (CFD), by exemplification with 4 patients treated with an endograft for occlusive disease of the superficial femoral artery (SFA). The potential of personalized CFD for predicting endograft thrombosis is investigated.

MATERIALS AND METHODS

Four patients treated with endografts for an occluded SFA were retrospectively included. CFD simulations, based on CTA and duplex ultrasound, were compared for patients with and without endograft thrombosis to investigate potential flow-related causes of endograft thrombosis. Time-averaged wall shear stress (TAWSS) was computed, which highlights areas of prolonged residence times of coagulation factors in the graft.

RESULTS

CFD simulations demonstrated normal TAWSS (>0.4 Pa) in the SFA for cases 1 and 2, but low levels of TAWSS (<0.4 Pa) in cases 3 and 4, respectively. Primary patency was achieved in cases 1 and 2 for over 2 year follow-up. Cases 3 and 4 were complicated by recurrent endograft thrombosis.

CONCLUSION

The presence of a low TAWSS was associated with recurrent endograft thrombosis in subjects with otherwise normal anatomic and ultrasound assessment and a good distal run-off.

[Changes in deep femoral artery topography during open revascularization of the lower limbs]

OBJECTIVE

To study topographic changes of femoral triangle arteries during open revascularization of the lower limbs.

MATERIAL AND METHODS

A retrospective study included 30 men aged 59.6±3 years with atherosclerotic femoropopliteal occlusion and chronic lower limb ischemia IIb-III stage according to the Pokrovsky-Fontaine classification. All patients underwent open reconstructive interventions. Ten patients underwent above-knee femoropopliteal replacement with a synthetic prosthesis, 10 patients - above-knee femoropopliteal bypass with a synthetic prosthesis, 7 patients - above-knee femoropopliteal bypass with autologous vein, 3 patients - below-knee femoropopliteal bypass with autologous vein. Control group consisted of 30 healthy mean aged 60±2 years. Ultrasound was carried out using the Esaote My Lab Alfa scanner (3-12 MHz linear transducer and 3-5 MHz convex transducer).

RESULTS

In healthy volunteers, deep femoral artery always arose from common femoral artery under the angle ≤30° in all cases (20° - 93.3% of cases, 30° - 6.7% of cases). In patients with previous surgical treatment, angle of deep femoral artery varied from 35 to 80°. After femoropopliteal bypass grafting with autologous vein, angle of deep femoral artery varied from 35 to 45° (35° - 8 patients, 40° - 1 patient, 45° - 1 patient). After femoropopliteal bypass grafting with a synthetic prosthesis, angle of deep femoral artery increased up to 40-50° (40° - 2 patients, 50° - 8 patients). In case of previous femoropopliteal replacement with a synthetic prosthesis, angle of deep femoral artery increased up to 70-80° (70° - 7 patients, 75° - 2 patients, 80° - 1 patient).

CONCLUSION

Normally, angle of deep femoral artery does not exceed 30°. Open reconstructive surgery on femoropopliteal arteries increases this value from 30° to 80°. Minimal changes are observed after femoropopliteal bypass grafting with autologous vein.

In-Flow dynamics of an area-difference-energy spring-particle red blood cell model on non-uniform grids

In this paper the area-difference-energy spring-particle (ADE-SP) red blood cell (RBC) structural model developed by Chen and Boyle is coupled with a lattice Boltzmann flux solver to simulate RBC dynamics. The novel ADE-SP model accounts for bending resistance due to the membrane area difference of RBCs while the lattice Boltzmann flux solver offers reduced computational runtimes through GPU parallelisation and enabling the employment of non-uniform meshes. This coupled model is used to simulate RBC dynamics and predictions are compared with existing experimental measurements. The simulations successfully predict tumbling, tank-treading, swinging and intermittent behaviour of an RBC in shear flow, and demonstrate the capability of the model in capturing in-flow RBC behaviours.

Case Studies in Physiology: Visualization of blood recirculation in a femoral artery "trifurcation" using ultrasound vector flow imaging

The femoral bifurcation is typically composed of a common femoral artery that bifurcates into the superficial (SFA) and deep (DFA) femoral arteries, with the lateral circumflex femoral artery (LCFA) branching distal to the origin of the DFA. We report a unique case of a 22-yr-old woman with a femoral "trifurcation," where the origin of the LCFA coincides with the origin of the DFA, resulting in a true three-way branching of the common femoral artery. We characterized the complex hemodynamics of the trifurcation region with ultrasound vector flow imaging at rest, and during 80 mmHg cuff compression of the calf to induce greater oscillatory blood flow. At rest, a clear trifurcation is observed with color Doppler imaging, while vector flow imaging further revealed a large area of flow circulation proximal to the LCFA and DFA. Cuff compression reduced SFA blood flow to 0 cm³/min, characterized by almost constant retrograde blood flow throughout diastole. When visualized with vector flow imaging, diastolic retrograde blood flow from the SFA appeared to reperfuse the DFA and LCFA during late systole, eliminating the retrograde flow component and providing a secondary source of anterograde blood flow to the thigh. In a rare case of a femoral trifurcation, we demonstrate blood recirculation patterns at rest, as well as collateral retrograde blood flow redistribution during lower limb compression. While it is unknown whether these trifurcation findings extend to typical bifurcations, it is evident that advanced methods of blood flow characterization are necessary to visualize and study complex vascular regions.NEW & NOTEWORTHY A femoral "trifurcation" is observed when the lateral circumflex femoral artery has an atypical proximal origin, branching at the same level as the superficial and deep femoral arteries. Ultrasound vector flow imaging at 750 fps was able to reveal substantial blood recirculation within the trifurcation at rest, as well as unique redistribution of blood flow between downstream branches during external cuff manipulation of retrograde flow, indicating novel ways in which diastolic blood flow is controlled.

Fluid–Solid Interaction Analysis on Iliac Bifurcation Artery: A Numerical Study

Atherosclerosis, which is commonly seen at regions with low wall shear stress (WSS) level in bifurcations, is a kind of fibro-fatty plaque accumulated on arterial walls. Aortic and iliac bifurcations have the highest proportion of patients among all atherosclerosis cases, thus it is necessary to numerically analyze the flow distribution and predict plaque positions in these bifurcations. Furthermore, using fluid–solid interaction (FSI) method could obtain a more exact flow pattern in arteries. In this study, a patient-specific model of aortic and iliac bifurcations was simulated with both FSI and rigid-wall cases. We analyzed the vessel deformation, WSS and flow distribution of this model. Computed tomography (CT) angiography was used in our study to create patient-specific model of aorto-iliac arteries. Real material properties and pulsatile fluid boundary conditions were applied in solid and fluid zones, respectively. We performed FSI and ordinary computational fluid dynamics (CFD) simulations with AYSYS 15.0 software (ANSYS Inc., Canonsburg, PA), and compared the diameter change, WSS and flow field between these two results. The diameter change between systolic phase and diastolic phase is 8–9% on abdominal aorta, and 3% on external and internal iliac arteries. The compliance of vessels corresponds to in-vivo observations. At peak systolic phase, the average WSS obtained in FSI simulation is 10% lower than in rigid-wall result, area of low-WSS region ([Formula: see text]) also increases by 78%. Wall deformation has a greater impact on WSS of those vessels with larger diameter, but hardly changes the shear level in smaller branches. Our result also shows that iliac bifurcations reveal more complicated secondary flow in systolic phase, comparing to other vessels, and stenosed iliac artery has more severe secondary flow than healthy artery. We obtained a feasible method for hemodynamic FSI research. The material parameters, boundary conditions and mesh could be used for further simulations, while the WSS and flow distribution may support clinical diagnosis and treatment. We concluded that compliance is a must-consider factor for simulating an accurate wall shear stress, because the vessel deformation in FSI simulation will significantly change the distribution of low-WSS zones. Moreover, more complicated secondary flow is detected in iliac arteries because it may interact between bifurcations. Stenosis in artery may also have a blocking effect on downstream blood flow.

Modeling of a fast-response magnetic-sensitive hydrogel for dynamic control of microfluidic flow

A magnetic-sensitive hydrogel-based microfluidic system is designed via a magneto-chemo-hydro-mechanical model for replicating various physiological and pathological conditions in the human body, by which the desired flow patterns can be generated in real time due to the fast-response deformation of the magnetic hydrogel. In the model, the fluid-structure interaction is characterized between the deformable magnetic hydrogel and surrounding fluid flow through the fully coupled arbitrary Lagrangian-Eulerian (ALE) method. Moreover, the physicochemical mechanisms including hydrogel magnetization, fluid diffusion, fluid flow, and hydrogel large deformation are characterized. After validation of the present model with both the finite difference and experimental results in the open literature, the transient behavior of the magnetic hydrogel is investigated, and the results show that the response time for the magnetic hydrogel is improved significantly in a uniform magnetic field compared with that of a hydrogel without the magnetic effect. Furthermore, various patterns of pulsatile flow are generated for mimicking the cell physiological microenvironment experienced by bone marrow stromal cells, and also for the pathological condition at the femoral artery during diastole and systole, respectively. Therefore, the present magnetic-sensitive hydrogel-based microfluidic system via the multiphysics model may provide a relevant humanized manipulation platform to investigate cell behavior and function through microfluidic chips.

Development of a Computational Fluid Dynamics Model for Myocardial Bridging

Computational fluid dynamics (CFD) modeling of myocardial bridging (MB) remains challenging due to its dynamic and phasic nature. This study aims to develop a patient-specific CFD model of MB. There were two parts to this study. The first part consisted of developing an in silico model of the left anterior descending (LAD) coronary artery of a patient with MB. In this regard, a moving-boundary CFD algorithm was developed to simulate the patient-specific muscle compression caused by MB. A second simulation was also performed with the bridge artificially removed to determine the hemodynamics in the same vessel in the absence of MB. The second part of the study consisted of hemodynamic analysis of three patients with mild and moderate and severe MB in their LAD by means of the developed in silico model in the first part. The average shear stress in the proximal and bridge segments for model with MB were significantly different from those for model without MB (proximal segment: 0.32 ± 0.14 Pa (with MB) versus 0.97 ± 0.39 Pa (without MB), P < 0.0001 — bridge segment: 2.60 ± 0.94 Pa (with MB) versus 1.50 ± 0.64 Pa (without MB), P < 0.0001). When all three patients were evaluated, increasing the degree of vessel compression shear stress in the proximal segment decreased, whereas the shear stress in the bridge segment increased. The presence of MB resulted in hemodynamic abnormalities in the proximal segment, whereas segments within the bridge exhibited hemodynamic patterns which tend to discourage atheroma development.