Experimental and numerical investigation of pulsed flows in asevere aortic stenosed model

Influence of vascular embolism level and drug injection rate on thrombolytic therapy of bifurcated femoral vein: Numerical simulation and validation study

BACKGROUND AND OBJECTIVE

Deep vein thrombosis (DVT) of the lower limbs is a critical global vascular disease. Accurately assessing and predicting the efficacy of DVT treatment remains a significant challenge due to a lack of understanding of the mechanisms by which the level of patient-specific embolization and the rate of drug injection affect thrombolytic therapy.

METHODS

In this study, we used the computed tomographic venography (CTV) clinical method to obtain patient-specific parameters, and the flow-solid interaction (FSI) method combined with biochemical response modeling of thrombolysis to analyze patient-specific hemodynamic and biomechanical characteristics and to quantitatively assess the effects of three vessel embolism levels (VEL) versus two drug injection rates (DIR) on bifurcated femoral venous thrombolytic therapy. In addition, we verified the reliability of the simulation results by in vitro thrombolytic therapy experiments.

RESULTS

In the bifurcated femoral vein, the state of blood flow, vortex, wall shear stress (WSS), time-averaged wall shear stress (TAWSS), vessel wall pressure, leaflet motion displacement, and valve von Mises stress vary with thrombus size and vessel shape. Venous valves accelerate blood flow, producing a jet phenomenon. From the numerical and experimental results, thrombolytic therapy should select the injection rate according to the severity of the thrombus. Rapid injection restores flow in mild thrombosis, while slow injection ensures gradual drug penetration for serious thrombosis.

CONCLUSIONS

The present study found that the hemodynamic parameters and biomechanical characteristics explored are closely related to the efficacy of thrombolytic therapy. Both hemodynamic parameters and biomechanical characteristics are affected by blood flow velocity. At the same time, the study also revealed the mechanism of the influence of VTE and DIR on bifurcated venous thrombolytic therapy, to provide a scientific basis for clinicians to formulate more precise treatment strategies.

A Comprehensive Review of Contemporary Bioreactors for Vascular Inflammation Studies

The field of vascular biology has advanced significantly with bioreactor systems, which have become essential tools for investigating the mechanisms of vascular inflammatory diseases such as atherosclerosis, vasculitis, and aneurysms. These bioreactors allow researchers to recreate specific vascular environments, providing a controlled setting for studying the effects of blood flow, mechanical stress, and biochemical factors on vascular tissues. Through these systems, researchers can explore how physical and chemical cues contribute to disease processes and cellular responses, enhancing our understanding of disease progression. Bioreactor studies have demonstrated that hemodynamic forces, particularly shear stress, influence endothelial cell behavior and play a role in vascular pathologies. For instance, in atherosclerosis, disturbed flow patterns are associated with endothelial dysfunction and plaque development. By simulating these conditions, bioreactors provide insight into the effects of mechanical forces on vascular wall biology, highlighting how altered flow can contribute to disease. Bioreactors also support studies on the impacts of pulsatile flow and circumferential stress, allowing a closer approximation of physiological environments. Beyond flow dynamics, these systems facilitate investigation into how vascular cells respond to biochemical signals, inflammatory markers, and therapeutic interventions. This integrated approach allows for a more complete picture of the factors involved in vascular disease. Recent advancements, such as vessel-on-a-chip models and artery-mimicking setups, extend the capabilities of bioreactors by enabling researchers to model a broader range of conditions relevant to human physiology. In vasculitis studies, bioreactors help explore immune interactions with endothelial cells, especially with stem cell-derived cells that replicate patient-specific responses. Bioreactors also play a role in vascular tissue engineering, particularly in assessing materials and scaffold-free designs that may reduce inflammation in vascular grafts. These efforts contribute to the ongoing search for more compatible graft materials, with the potential to improve outcomes in clinical applications. This review provides a comprehensive overview of bioreactor technologies applied in vascular inflammation research, examining their designs, applications, and contributions to disease modeling. Organized into sections on bioreactor configurations, flow dynamics, biochemical interactions, and tissue engineering applications, the review concludes by discussing recent innovations and highlighting directions for future research, underscoring the role of bioreactors in bridging laboratory studies with insights into vascular disease.

Assessing turbulent effects in ascending aorta in presence of bicuspid aortic valve

Aortic valves with bicuspids have two rather than three leaflets, which is a congenital heart condition. About 0.5-2% of people have a bicuspid aortic valve. Blood flow through the aorta is commonly believed to be laminar, although aortic valve disorders can cause turbulent transitions. Understanding the impact of turbulence is crucial for foreseeing how the disease will progress. The study's objective was use large eddy simulation to provide a thorough analysis of the turbulence in bicuspid aortic valve dysfunction. Using a large eddy simulation, the blood flow patterns of the bicuspid and tricuspid aortic valves were compared, and significant discrepancies were found. The velocity field in flow in bicuspid configurations was asymmetrically distributed toward the ascending aorta. In tricuspid aortic valve (TAV) the flow, on the other hand, was symmetrical within the same aortic segment. Moreover, we looked into standard deviation, Q-criterion, viscosity ratio and wall shear stresses for each cases to understand transition to turbulence. Our findings indicate that in the bicuspid aortic valve (BAV) case, the fluid-dynamic abnormalities increase. The global turbulent kinetic energy and time-averaged wall shear stress for the TAV and BAV scenarios were also examined. We discovered that the global turbulent kinetic energy was higher in the BAV case compared to TAV, in addition to the increased wall shear stress induced by the BAV in the ascending aorta.

Smartphone-based particle tracking velocimetry for the in vitro assessment of coronary flows

The present study adopts a smartphone-based approach for the experimental characterization of coronary flows. Technically, Particle Tracking Velocimetry (PTV) measurements were performed using a smartphone camera and a low-power continuous wave laser in realistic healthy and stenosed phantoms of left anterior descending artery with inflow Reynolds numbers approximately ranging from 20 to 200. A Lagrangian-Eulerian mapping was performed to convert Lagrangian PTV velocity data to a Eulerian grid. Eulerian velocity and vorticity data obtained from smartphone-based PTV measurements were compared with Particle Image Velocimetry (PIV) measurements performed with a smartphone-based setup and with a conventional setup based on a high-power double-pulsed laser and a CMOS camera. Smartphone-based PTV and PIV velocity flow fields substantially agreed with conventional PIV measurements, with the former characterized by lower average percentage differences than the latter. Discrepancies emerged at high flow regimes, especially at the stenosis throat, due to particle image blur generated by smartphone camera shutter speed and image acquisition frequency. In conclusion, the present findings demonstrate the feasibility of PTV measurements using a smartphone camera and a low-power light source for the in vitro characterization of cardiovascular flows for research, industrial and educational purposes, with advantages in terms of costs, safety and usability.

Numerical simulation and experimental validation of thrombolytic therapy for patients with venous isomer and normal venous valves

Thrombus is an extremely dangerous factor in the human body that can block the blood vessel. Once thrombosis happens in venous of lower limbs, local blood flow is impeded. This leads to venous thromboembolism (VTE) and even pulmonary embolism. In recent years, venous thromboembolism has frequently occurred in a variety of people, and there is no effective treatment for patients with different venous structures. For the patients with venous isomer with single valve structure, we establish a coupled computational model to simulate the process of thrombolysis with multi-dose treatment schemes by considering the blood as non-Newtonian fluid. Then, the corresponding in vitro experimental platform is built to verify the performance of the developed mathematical model. At last, the effects of different fluid models, valve structures and drug doses on thrombolysis are comprehensively studied through numerical and experimental observations. Comparing with the experimental results, the relative error of blood boosting index (BBI) obtained from non-Newtonian fluid model is 11% smaller than Newtonian fluid. In addition, the BBI from venous isomer is 1300% times stronger than patient with normal venous valve while the valve displacement is 500% times smaller. As consequence, low eddy current and strong molecular diffusion near the thrombus in case of isomer promote thrombolysis rate up to 18%. Furthermore, the 80 μM dosage of thrombolytic drugs gets the maximum thrombus dissolution rate 18% while the scheme of 50 μM doses obtains a thrombolysis rate of 14% in case of venous isomer. Under the two administration schemes for isomer patients, the rates from experiments are around 19.1% and 14.9%, respectively. It suggests that the proposed computational model and the designed experiment platform can potentially help different patients with venous thromboembolism to carry out clinical medication prediction.

The counterbalance of endothelial glycocalyx and high wall shear stress to low-density lipoprotein concentration polarization in mouse ear skin arterioles

BACKGROUND AND AIMS

Atherosclerosis preferentially occurs at regions in arterial branching, curvature, and stenosis, which may be explained by the geometric predilection of low-density lipoprotein (LDL) concentration polarization that has been investigated in major arteries in previous studies. Whether this also happens in arterioles remains unknown.

METHODS

Herein, a radially non-uniform distribution of LDL particles and a heterogeneous endothelial glycocalyx layer in the mouse ear arterioles, as shown by fluorescein isothiocyanate labeled wheat germ agglutinin (WGA-FITC), were successfully observed by a non-invasive two-photon laser-scanning microscopy (TPLSM) technique. The stagnant film theory was applied as the fitting function to evaluate LDL concentration polarization in arterioles.

RESULTS

The concentration polarization rate (CPR, the ratio of the number of polarized cases to that of total cases) in the inner walls of curved and branched arterioles was 22% and 31% higher than the outer counterparts, respectively. Results from the binary logistic regression and multiple linear regression analysis showed that endothelial glycocalyx thickness increases CPR and the thickness of the concentration polarization layer (CPL). Flow field computation indicates no obvious disturbances or vortex in modeled arterioles with different geometries and the mean wall shear stress is about 7.7-9.0 Pa.

CONCLUSIONS

These findings suggest a geometric predilection of LDL concentration polarization in arterioles for the first time, and the existence of an endothelial glycocalyx, acting together with a relatively high wall shear stress in arterioles, may explain to some extent why atherosclerosis rarely occurs in these regions.