Effect of valve lesion on venous valve cycle: A modified immersed finite element modeling

Venous thromboembolism: diagnostic advances and unaddressed challenges in management

PURPOSE OF REVIEW

This review summarizes recent advances in developing targeted diagnostics for venous thromboembolism (VTE) and unaddressed knowledge gaps in patient management. Without addressing these critical data needs, the morbidity in VTE patients will persist.

RECENT FINDINGS

Recent studies investigating plasma protein profiles in VTE patients have identified key diagnostic targets to address the currently unmet need for low-cost, confirmatory, point-of-care VTE diagnostics. These studies and a growing body of evidence from animal model studies have revealed the importance of inflammatory and vascular pathology in driving VTE, which are currently unaddressed targets for VTE therapy. To enhance the translation of preclinical animal studies, clinical quantification of thrombus burden and comparative component analyses between modeled VTE and clinical VTE are necessary.

SUMMARY

Lead candidates from protein profiling of VTE patients' plasma offer a promising outlook in developing low cost, confirmatory, point-of-care testing for VTE. Additionally, addressing the critical knowledge gap of quantitatively measuring clinical thrombi will allow for an array of benefits in VTE management and informing the translatability of experimental therapeutics.

Bidirectional perforators in the lower limb are not physiologically normal: A brief commentary

The suggestion that bidirectional flow is a normal feature seen in venous perforators of the lower leg has been a longstanding debate. Newer published evidence has changed the perspective on normal perforator flow and is presented here to resolve the misunderstandings and different viewpoints previously held.

Effect of intermittent pneumatic compression on preventing deep vein thrombosis using microfluidic vein chip

Background: Deep Vein Thrombosis (DVT) is a common disease, frequently afflicting the lower limb veins of bedridden patients. Intermittent Pneumatic Compression (IPC) is often employed as an effective solution for this problem. In our study, a random selection of 264 patients underwent IPC treatment for either one or 8 hours daily. The rate of severe venous thrombosis was substantially reduced in the IPC-treated group compared to the control group. However, real-time monitoring of blood flow during IPC operation periods remains a challenge, leading to rare awareness of IPC working mechanism on thrombosis prevention. Methods: Here, microfluidic chip methodology is used to create an in vitro vein-mimicking platform integrating venous valves in a deformable channel. Whole blood of patients after knee surgery was perfused into the venous channel at a controlled flow rate obtained from patients with IPC treatment clinically. Results: According to the numerical simulations results, both of an increase in compressive pressure and a decrease in time interval of IPC device can accelarete blood flow rate and the shear stress within the vein. The vein chip experiments also reveal that the fibrin accumulation can be greatly lowered in IPC treated group, indicating less thrombosis formation in future. A time interval of 24 seconds and a maximum contraction pressure of 40 mmHg were proved to be the most effective parameters for the IPC device adopted in our clinical trail. Conclusion: This vein chip presents a novel method for observing the functional mechanisms of IPC device for DVT prevention. It provides crucial data for further standardization and optimization of IPC devices in clinical usage.

Platelet accumulation in an endothelium-coated elastic vein valve model of deep vein thrombosis is mediated by GPIbα-VWF interaction

Deep vein thrombosis is a life-threatening disease that takes millions of people's lives worldwide. Given both technical and ethical issues of using animals in research, it is necessary to develop an appropriate in vitro model that would recapitulate the conditions of venous thrombus development. We present here a novel microfluidics vein-on-a-chip with moving valve leaflets to mimic the hydrodynamics in a vein, and Human Umbilical Vein Endothelial Cell (HUVEC) monolayer. A pulsatile flow pattern, typical for veins, was used in the experiments. Unstimulated human platelets, reconstituted with the whole blood, accumulated at the luminal side of the leaflet tips proportionally to the leaflet flexibility. Platelet activation by thrombin induced robust platelet accrual at the leaflet tips. Inhibition of glycoprotein (GP) IIb-IIIa did not decrease but, paradoxically, slightly increased platelet accumulation. In contrast, blockade of the interaction between platelet GPIbα and A1 domain of von Willebrand factor completely abolished platelet deposition. Stimulation of the endothelium with histamine, a known secretagogue of Weibel-Palade bodies, promoted platelet accrual at the basal side of the leaflets, where human thrombi are usually observed. Thus, platelet deposition depends on the leaflet flexibility, and accumulation of activated platelets at the valve leaflets is mediated by GPIbα-VWF interaction.

Effects of non-Newtonian viscosity on arterial and venous flow and transport

It is well known that blood exhibits non-Newtonian viscosity, but it is generally modeled as a Newtonian fluid. However, in situations of low shear rate, the validity of the Newtonian assumption is questionable. In this study, we investigated differences between Newtonian and non-Newtonian hemodynamic metrics such as velocity, vorticity, and wall shear stress. In addition, we investigated cardiovascular transport using two different approaches, Eulerian mass transport and Lagrangian particle tracking. Non-Newtonian solutions revealed important differences in both hemodynamic and transport metrics relative to the Newtonian model. Most notably for the hemodynamic metrics, in-plane velocity and vorticity were consistently larger in the Newtonian approximation for both arterial and venous flows. Conversely, wall shear stresses were larger for the non-Newtonian case for both the arterial and venous models. Our results also indicate that for the Lagrangian metrics, the history of accumulated shear was consistently larger for both arterial and venous flows in the Newtonian approximation. Lastly, our results also suggest that the Newtonian model produces larger near wall and luminal mass transport values compared to the non-Newtonian model, likely due to the increased vorticity and recirculation. These findings demonstrate the importance of accounting for non-Newtonian behavior in cardiovascular flows exhibiting significant regions of low shear rate and recirculation.

Advances in Engineering Venous Valves: The Pursuit of a Definite Solution for Chronic Venous Disease

Native venous valves enable proper return of blood to the heart. Under pathological conditions (e.g., chronic venous insufficiency), venous valves malfunction and fail to prevent backward flow. Clinically, this can result in painful swelling, varicose veins, edema, and skin ulcerations leading to a chronic wound situation. Surgical correction of venous valves has proven to drastically reduce these symptoms. However, the absence of intact leaflets in many patients limits the applicability of this strategy. In this context, the development of venous valve replacements represents an appealing approach. Despite acceptable results in animal models, no venous valve has succeeded in clinical trials, and so far no single prosthetic venous valve is commercially available. This calls for advanced materials and fabrication approaches to develop clinically relevant venous valves able to restore natural flow conditions in the venous circulation. In this study, we critically discuss the approaches attempted in the last years, and we highlight the potential of tissue engineering to offer new avenues for valve fabrication. Impact statement Venous valves prosthesis offer the potential to restore normal venous flow, and to improve the prospect of patients that suffer from chronic venous disease. Current venous valve replacements are associated with poor outcomes. A deeper understanding of the approaches attempted so far is essential to establish the next steps toward valve development, and importantly, tissue engineering constitutes a unique toolbox to advance in this quest.

Fluid-structure interaction of blood flow around a vein valve

Introduction: Venous valves are a type of one-way valves which conduct blood flow toward the heart and prevent its backflow. Any malfunction of these organs may cause serious problems in the circulatory system. Numerical simulation can give us detailed information and point to point data such as velocity, wall shear stress, and von Mises stress from veins with small diameters, as obtaining such data is almost impossible using current medical devices. Having detailed information about fluid flow and valves' function can help the treatment of the related diseases. Methods: In the present work, the blood flow through a venous valve considering the flexibility of the vein wall and valve leaflets is investigated numerically. The governing equations of fluid flow and solid domain are discretized and solved by the Galerkin finite element method. Results: The obtained results showed that the blood velocity increases from inlet to the leaflets and then decreases passing behind the valve. A pair of vortices and the trapped region was observed just behind the valves. These regions have low shear stresses and are capable of sediment formation. Conclusion: The von Mises stress which is a criterion for the breakdown of solid materials was obtained. It was also observed that a maximum value occurred at the bottom of the leaflets.