Flow Effects on Coagulation and Thrombosis

A mathematical model for activated platelet-dependent activation of coagulation factor X by factor IXa

Membrane-dependent enzymatic reactions are central in many signaling and regulatory biological networks. Activation of blood coagulation factor X by activated factor IXa is a classical example, which retains many mysteries and controversies. Here we developed a novel non-stationary two-compartment computational model of this reaction on the physiological membrane of activated platelets (rather than phospholipid vesicles) within a wide platelet concentration range up to the intra-thrombus conditions, which took into account novel essential revisions in the mechanisms on factor IXa interactions with platelets. The set of ordinary differential equations (ODEs) was based on the laws of mass action and included several possible pathways of the complex formation. Sensitivity analysis was employed to identify critical points in the regulation. The model was able to describe the available experimental data and suggested that the major pathways of the enzyme-substrate complex assembly were membrane-dependent and solution-dependent enzyme delivery, with comparable contributions. The dependence of factor Xa formation on the activated procoagulant platelet concentration was predicted to be bell-shaped with the peak at (1.5-2)·106 platelets/μL, which is similar to the expected intra-thrombus concentration. The modeling of the kinetics of all model variables demonstrated two-phase kinetics. With increasing platelet concentration in the system, the transition time after which a stationary concentration is reached increases to approximately 5 min.

3D bioprinting of collagen-based high-resolution internally perfusable scaffolds for engineering fully biologic tissue systems

Organ-on-a-chip and microfluidic systems have improved the translational relevance of in vitro systems; however, current manufacturing approaches impart limitations on materials selection, non-native mechanical properties, geometric complexity, and cell-driven remodeling into functional tissues. Here, we three-dimensionally (3D) bioprint extracellular matrix (ECM) and cells into collagen-based high-resolution internally perfusable scaffolds (CHIPS) that integrate with a vascular and perfusion organ-on-a-chip reactor (VAPOR) to form a complete tissue engineering platform. We improve the fidelity of freeform reversible embedding of suspended hydrogels (FRESH) bioprinting to produce a range of CHIPS designs fabricated in a one-step process. CHIPS exhibit size-dependent permeability of perfused molecules into the surrounding scaffold to support cell viability and migration. Lastly, we implemented multi-material bioprinting to control 3D spatial patterning, ECM composition, cellularization, and material properties to create a glucose-responsive, insulin-secreting pancreatic-like CHIPS with vascular endothelial cadherin+ vascular-like networks. Together, CHIPS and VAPOR form a platform technology toward engineering full organ-scale function for disease modeling and cell replacement therapy.

Breaking the Limitation of Laminar Flow in Thrombolytic Therapy with Reconfigurable Vortex-Like Nanobot Swarms

Laminar blood flow represents the normal physiological state of blood circulation, but it also acts as a natural physiological barrier for the effective diffusion of drugs to the lesion site. Here, we report a bioinspired strategy in which reconfigurable vortex-like swarms of magnetic swimming nanobots actively disrupt the laminar flow to deliver drugs in a manner similar to how bacteria seek food. The drug was released from the cavity of biodegradable, submicron pentosan flask-like nanobots, aggregates as the dynamic rotating drug fluid under a rotating magnetic field. The vortex-like nanobot swarm successfully overcame the laminar barrier near the thrombus in a rat inferior vena cava stenosis thrombosis model, which was observed by ultrasound blood flow imaging. Furthermore, the clinical feasibility of nanobots swarm for enhancing thrombolytic efficacy through drug aggregation after breaking the laminar flow was further confirmed in a rat deep vein thrombosis model. This bionic active targeting approach overcomes the laminar flow barrier and restricts the release of drugs by the swarm-induced vortex fluid to facilitate targeted drug delivery, which is expected to be an innovative method to enhance drug delivery efficiency.

Cardiomyopathy and thrombogenesis in cats through left atrial morphological and fluid dynamics analysis

The relationship between atrial fibrillation (AF), blood flow disturbances and thrombus formation is well-established in humans. Thrombi primarily form in the left atrial appendage (LAA), but the specific role of LAA morphology remains unclear. Felines, despite rarely experiencing AF, present a valuable model for studying human heart diseases. Cats exhibit a high incidence of cardiomyopathies, often accompanied by significant left atrial dilation and thrombus formation. This unique aspect prompts research focusing on LAA morphology and function in relation to thrombus development. Our study, using advanced image processing and fluid simulations on 24 cat hearts ranging from normal to cardiomyopathy subjects, aims to find distinctions in left atrium (LA) and LAA morphologies, blood flow patterns and their relation to thrombus formation. Significantly different variables in feline heart groups included: heart weight, LAA volume, LA volume, ostium area, ostium area-to-heart weight ratio, centreline length and velocity at the LAA ostium. Fluid simulations revealed lower LAA blood flow velocities and increased thrombotic risk in cases with thrombi. Our study enhances the understanding of LAA structure and function, offering insights into thrombus formation mechanisms with potential implications for better managing thrombosis risk in patients.

Mechanisms of aortic dissection: From pathological changes to experimental and in silico models

Aortic dissection continues to be responsible for significant morbidity and mortality, although recent advances in medical data assimilation and in experimental and in silico models have improved our understanding of the initiation and progression of the accumulation of blood within the aortic wall. Hence, there remains a pressing necessity for innovative and enhanced models to more accurately characterize the associated pathological changes. Early on, experimental models were employed to uncover mechanisms in aortic dissection, such as hemodynamic changes and alterations in wall microstructure, and to assess the efficacy of medical implants. While experimental models were once the only option available, more recently they are also being used to validate in silico models. Based on an improved understanding of the deteriorated microstructure of the aortic wall, numerous multiscale material models have been proposed in recent decades to study the state of stress in dissected aortas, including the changes associated with damage and failure. Furthermore, when integrated with accessible patient-derived medical data, in silico models prove to be an invaluable tool for identifying correlations between hemodynamics, wall stresses, or thrombus formation in the deteriorated aortic wall. They are also advantageous for model-guided design of medical implants with the aim of evaluating the deployment and migration of implants in patients. Nonetheless, the utility of in silico models depends largely on patient-derived medical data, such as chosen boundary conditions or tissue properties. In this review article, our objective is to provide a thorough summary of medical data elucidating the pathological alterations associated with this disease. Concurrently, we aim to assess experimental models, as well as multiscale material and patient data-informed in silico models, that investigate various aspects of aortic dissection. In conclusion, we present a discourse on future perspectives, encompassing aspects of disease modeling, numerical challenges, and clinical applications, with a particular focus on aortic dissection. The aspiration is to inspire future studies, deepen our comprehension of the disease, and ultimately shape clinical care and treatment decisions.

Antithrombotic coating with sheltered positive charges prevents contact activation by controlling factor XII-biointerface binding

Antithrombotic surfaces that prevent coagulation activation without interfering with haemostasis are required for blood-contacting devices. Such materials would restrain device-induced thrombogenesis and decrease the need for anticoagulant use, thereby reducing unwanted bleeding. Here, by optimizing the interactions with coagulation factor XII rather than preventing its surface adsorption, we develop a substrate-independent antithrombotic polymeric coating with sheltered positive charges. The antithrombic properties of the coating were demonstrated in vitro with human blood and in vivo using a carotid artery-jugular vein shunt model in rabbits. The coating exhibits a strong interaction with factor XII, but results in a low reciprocal activation of the contact pathway that triggers clot formation. These findings contradict the prevailing strategy of designing antithrombotic materials through protein-repelling surfaces. Overall, the polymeric coating we describe can benefit most blood-contacting devices and is a useful engineering guideline for designing surfaces with improved antithrombotic properties.

"Hot-dog-string" drug-eluting degradable stents for treating stenosis in tortuous arteries

Despite advances in cardiovascular technology, treating stenosis in tortuous arteries with balloon-expandable stents, typically deployed in a straight orientation, remains a challenge. This study developed novel balloon-expandable "hot-dog-string" (HDS) drug-eluting poly(ε-caprolactone) (PCL) nanofibrous stents using solvent casting and coaxial electrospinning techniques. A unique HDS geometry was designed for the PCL stent backbone, while aspirin and sirolimus were loaded into the core-sheath structured poly(lactic-co-glycolic acid) (PLGA) nanofibers, which were then wrapped around the degradable stent. In vitro characterization of the biodegradable HDS stent and drug-eluting nanofibers was conducted. The results indicate that the biodegradable HDS stents exhibited excellent mechanical properties and superior flexibility, allowing them to navigate curved sections of a simulated in vitro vessel model more effectively than metallic stents. The core-sheath structure of the nanofibers enabled sustained release of high concentrations of aspirin and sirolimus over 14 and 23 days, respectively, with sirolimus effectively inhibiting smooth muscle cell proliferation. Moreover, in vivo animal tests showed that the rabbits remained in good health with excellent vessel patency following stent placement. By implementing the innovative design and techniques proposed in this study, we anticipate fabricating biodegradable drug-eluting HDS stents of various sizes for diverse cardiovascular applications at curved lesions.

Surface Modification of Poly(dimethylsiloxane) Blood Flow Chambers with a Poly(ethylene glycol) Conjugate and Factor XII Inhibitor

This study is focused on the application of a dual surface coating on poly(dimethylsiloxane) (PDMS) flow chambers, which aims to inhibit the contact activation pathway of coagulation. Polyethylene glycol (PEG) is a commonly used biocompatible molecule due to its hydrophilic nature and capacity to reduce protein adsorption. Corn trypsin inhibitor (CTI) is a selective inhibitor of Factor XII, which is the initial factor responsible for activating the intrinsic pathway of coagulation. By sequentially applying these two coatings to PDMS substrates, we expect the PEG-CTI coating to decrease blood clot formation and reduce fibrinogen deposition on surfaces compared to uncoated surfaces. Our results indicate that the PEG-CTI coating was successful in significantly reducing both cell adsorption and fibrinogen deposition to the surfaces of PDMS flow chambers. This study is a step toward applying PEG-CTI surface coatings to PDMS microfluidic artificial lungs, in which the surface interaction between the PDMS lungs and blood is a critical issue that must be mitigated to realize the full potential of this exciting therapeutic tool.

The biological role and future therapeutic uses of nitric oxide in extracorporeal membrane oxygenation, a narrative review

BACKGROUND

Nitric oxide (NO) is a gas naturally produced by the human body that plays an important physiological role. Specifically, it binds guanylyl cyclase to induce smooth muscle relaxation. NO's other protective functions have been well documented, particularly its protective endothelial functions, effects on decreasing pulmonary vascular resistance, antiplatelet, and anticoagulation properties. The use of nitric oxide donors as vasodilators has been known since 1876. Inhaled nitric oxide has been used as a pulmonary vasodilator and to improve ventilation perfusion matching since the 1990s. It is currently approved by the United States Food and Drug Administration for neonates with hypoxic respiratory failure, however, it is used off-label for acute respiratory distress syndrome, acute bronchiolitis, and COVID-19.

PURPOSE

In this article we review the currently understood biological action and therapeutic uses of NO through nitric oxide donors such as inhaled nitric oxide. We will then explore recent studies describing use of NO in cardiopulmonary bypass and extracorporeal membrane oxygenation and speculate on NO's future uses.

Impact of Vein Wall Hyperelasticity and Blood Flow Turbulence on Hemodynamic Parameters in the Inferior Vena Cava with a Filter

Inferior vena cava (IVC) filters are vital in preventing pulmonary embolism (PE) by trapping large blood clots, especially in patients unsuitable for anticoagulation. In this study, the accuracy of two common simplifying assumptions in numerical studies of IVC filters-the rigid wall assumption and the laminar flow model-is examined, contrasting them with more realistic hyperelastic wall and turbulent flow models. Using fluid-structure interaction (FSI) and computational fluid dynamics (CFD) techniques, the investigation focuses on three hemodynamic parameters: time-averaged wall shear stress (TAWSS), oscillatory shear index (OSI), and relative residence time (RRT). Simulations are conducted with varying sizes of clots captured in the filter. The findings show that, in regions of high wall shear stress, the rigid wall model predicted higher TAWSS values, suggesting an increased disease risk compared to the hyperelastic model. However, the laminar and turbulent flow models did not show significant differences in TAWSS predictions. Conversely, in areas of low wall shear stress, the rigid wall model indicated lower OSI and RRT, hinting at a reduced risk compared to the hyperelastic model, with this discrepancy being more evident with larger clots. While the predictions for OSI and TAWSS were closely aligned for both laminar and turbulent flows, divergences in RRT predictions became apparent, especially in scenarios with very large clots.

Parasagittal dural arteriovenous fistulas

BACKGROUND

The majority of studies on parasagittal dural arteriovenous fistulas (DAVFs) have been limited to case reports or case series, and they are frequently reported alongside true superior sagittal sinus (SSS) DAVFs. Because of the selective bias present in the reporting of dispersed small numbers of parasagittal DAVFs, the results of each study may influence the findings. As a result, we present a large sequential cohort of parasagittal DAVFs from our institution spanning a 20-year period.

METHODS

This study was a retrospective analysis involving 80 patients with parasagittal DAVFs who were hospitalized at a single medical center from 2002 to 2022. We explore their clinical manifestations, angioarchitecture, clinical and radiographic outcomes.

RESULTS

We identified 80 patients with 85 parasagittal DAVFs. The cohort consisted of 69 men and 11 women, with a M ± SD age of 50.5 ± 11.1 years. Seventy-six patients underwent trans-arterial embolization (TAE), two underwent surgery, and two received conservative treatment. Immediate complete occlusion was achieved in 74 cases (94.9%). Fifty (96.2%) patients were cured, with no recurrence detected on final follow-up imaging. One patient died 6 months after the final subtotal occlusion, while the other patients experienced improvement or resolution of clinical symptoms following treatment.

CONCLUSIONS

These lesions carry a high risk of hemorrhage and nonhemorrhagic neurological deficits. In our series, TAE achieved a high cure rate for these lesions, with no major complications reported.

Design and simulation of a microfluidics-based artificial glomerular ultrafiltration unit to reduce cell-induced fouling

BACKGROUND

The microfluidic-based Glomerulus-on-Chips (GoC) are mostly cell based, that is, 3D cell culture techniques are used to culture glomerular cells in order to mimic glomerular ultrafiltration. These chips require high maintenance to keep cell viability intact. There have been some approaches to build non-cell-based GoCs but many of these approaches have the drawback of membrane fouling. This article presents a structural design and simulation study of a dialysate free microfluidic channel for replicating the function of the human glomerular filtration barrier. The key advancement of the current work is addressing the fouling issue by combining a pre-filter to eliminate cellular components and performing filtration on the blood plasma.

METHODS

The Laminar Flow Mixture Model in COMSOL Multiphysics 5.6 has been utilized to simulate the behavior of blood flow in the microchannels. The geometrical effect of microchannels on the separation of the filtrate was investigated. The velocity at the inlet of the microchannel and pore size of the filtration membrane are varied to see the change in outflow and filtration fraction.

RESULTS

The efficiency of the device is calculated in terms of the filtration fraction (FF%) formed. Simulation results show that the filtrate obtained is ~20% of the plasma flow rate in the channel, which resembles the glomerular filtration fraction.

CONCLUSION

Given that it is not dependent on the functionality of grown cells, the proposed device is anticipated to have a longer lifespan due to its non-cell-based design. The device's cost can be reduced by avoiding cell cultivation inside of it. It can be integrated as a glomerular functional unit with other units of kidney model to build a fully developed artificial kidney.

Bathing-Related Ischemic Stroke: Association between Stroke Subtype and Cerebral Small Vessel Disease

AIMS

Bathing-related ischemic stroke (BIS) is sometimes fatal. However, its mechanisms and risk factors remain unclear. We aimed to identify the incidence of stroke subtypes in BIS, and clarify the impact of cerebral small vessel disease (CSVD) on BIS.

METHODS

Consecutive patients with ischemic stroke between October 2012 and February 2022 were retrospectively screened. The inclusion criteria were: 1) onset-to-door time within 7 days; and 2) availability of the results of MRI evaluation of CSVD markers during hospitalization. BIS was defined as an ischemic stroke that occurred while or shortly after bathing. We investigated the incidence of the stroke subtype and the correlation between CSVD markers and BIS.

RESULTS

1,753 ischemic stroke patients (1,241 [71%] male, median age 69 years) were included. 57 patients (3%) were included in the BIS group. A higher frequency of large artery atherosclerosis (LAA) (prevalence ratio [PR] 2.069, 95% confidence interval [CI] 1.089 to 3.931, p=0.026) and lower frequency of cardio-embolism (CES) (PR 0.362, 95% CI 0.132 to 0.991, p=0.048) in BIS cases were identified. Moreover, lower periventricular hyperintensity (PVH) Fazekas grade (PR 0.671, 95% CI 0.472 to 0.956, p=0.027) and fewer cerebral microbleeds (CMBs) in deep brain region (PR 0.810, 95%CI 0.657 to 0.999, p=0.049) were associated with BIS cases.

CONCLUSIONS

The BIS group was more likely to develop LAA and less likely to develop CES. Lower PVH grade and fewer CMBs in deep brain region were associated with the development of BIS.

Analysis of bleeding outcomes in patients with hypoproliferative thrombocytopenia in the A-TREAT clinical trial

BACKGROUND

Despite prophylactic platelet transfusions, hypoproliferative thrombocytopenia is associated with bleeding; historical risk factors include hematocrit (HCT) ≤ 25%, activated partial thromboplastin time ≥ 30 s, international normalized ratio ≥ 1.2, and platelets ≤ 5000/μL.

METHODS

We performed a post hoc analysis of bleeding outcomes and risk factors in participants with hematologic malignancy and hypoproliferative thrombocytopenia enrolled in the American Trial to Evaluate Tranexamic Acid Therapy in Thrombocytopenia (A-TREAT) and randomized to receive either tranexamic acid (TXA) or placebo.

RESULTS

World Health Organization (WHO) grade 2+ bleeding occurred in 46% of 330 participants, with no difference between the TXA (44%) and placebo (47%) groups (p = 0.66). Overall, the most common sites of bleeding were oronasal (18%), skin (17%), gastrointestinal (11%), and genitourinary (11%). Among participants of childbearing potential, 28% experienced vaginal bleeding. Platelets ≤5000/μL and HCT < 21% (after adjusting for severe thrombocytopenia) were independently associated with increased bleeding risk (HR 3.78, 95% CI 2.16-6.61; HR 2.67, 95% CI 1.35-5.27, respectively). Allogeneic stem cell transplant was associated with nonsignificant increased risk of bleeding versus chemotherapy alone (HR 1.34, 95% CI 0.94-1.91).

DISCUSSION

The overall rate of WHO grade 2+ bleeding was similar to previous reports, albeit with lower rates of gastrointestinal bleeding. Vaginal bleeding was common in participants of childbearing potential. Platelets ≤5000/μL remained a risk factor for bleeding. Regardless of platelet count, bleeding risk increased with HCT < 21%, suggesting a red blood cell transfusion threshold above 21% should be considered to mitigate bleeding. More investigation is needed on strategies to reduce bleeding in this population.

Flow Dynamic Factors Correlated With Device-Related Thrombosis After Left Atrial Appendage Occlusion

Background

Device-related thrombosis (DRT) occurs in up to 4% of patients undergoing left atrial appendage occlusion (LAAO) and is associated with substantial morbidity and mortality. However, its pathophysiology, predictors, and optimal management remain unclear.

Objectives

This study aims to assess flow dynamic factors correlating to DRT.

Methods

A multicenter registry of patients who underwent LAAO and had pre- and post-computed tomography imaging was used. Patient-specific 3-dimensional digital models of the left atrium were created, and finite element simulations were performed to implant an LAAO device into each model in a position that matched the clinical deployment. Computational fluid dynamic simulations were performed to quantify the following flow dynamic parameters: time averaged wall shear stress, oscillatory shear index, and endothelial cell activation potential.

Results

A total of 38 patients (19 with DRT and 19 without DRT) were included. Left atrium volumes and mitral valve areas were larger in the DRT cohort compared with controls. Patients with DRT had a significantly lower time averaged wall shear stress (1.76 ± 1.24 Pa vs 2.90 ± 2.70 Pa), a higher oscillatory shear index (0.19 ± 0.11 vs 0.17 ± 0.11), and a higher endothelial cell activation potential (0.23 ± 0.58 Pa-1 vs 0.17 ± 0.30 Pa-1) than the controls (P < 0.001 for all). Thrombus locations identified from in-vivo images correlated well with the flow dynamic parameters tested.

Conclusions

Flow dynamic parameters may be able to predict the risk of DRT after LAAO. Further investigation with a larger patient cohort and long-term follow-up is needed to assess the role of computational fluid dynamics in the risk stratification of patients considered for LAAO.

The Basic Principles of Pathophysiology of Venous Thrombosis

The past few decades have brought tremendous insight into the molecular and pathophysiological mechanisms responsible for thrombus generation. For a clinician, it is usually sufficient to explain the incident of deep vein thrombosis (DVT) with provoking factors such as trauma with vascular injury, immobilization, hormonal factors, or inherited or acquired coagulation defects. About half of DVTs are, however, lacking such triggers and are called unprovoked. Venous stasis and hypoxia at the valve sinus level may start a chain of reactions. The concept of immunothrombosis has added a new dimension to the old etiological triad of venous stasis, vessel wall injury, and changes in blood components. This is particularly important in COVID-19, where hyperinflammation, cytokines, and neutrophil extracellular traps are associated with the formation of microthrombi in the lungs. To better understand the mechanisms behind DVT and reach beyond the above-mentioned simplifications, animal models and clinical epidemiological studies have brought insight into the complex interplay between leukocytes, platelets, endothelium, cytokines, complements, and coagulation factors and inhibitors. These pathways and the interplay will be reviewed here, as well as the roles of cancer, anticancer drugs, and congenital thrombophilic defects on the molecular level in hypercoagulability and venous thromboembolism.

Residual Red Blood Cell Volume in Extracorporeal Blood Circuit after Hemodialysis: A Single-Center Study

INTRODUCTION

The factors contributing to blood loss during hemodialysis (HD) procedures remain underexplored. This study aimed to quantify blood loss during HD and identify the potential factors associated with it.

METHODS

The study included 70 ESRD patients undergoing HD. After dialysis, the extracorporeal blood circuits were rinsed with 1,000 mL of 0.05% NH3 solution in distilled water, and hemoglobin levels were measured. Univariate regression was used to assess the linear relationship between residual red blood cell (RBC) volume and various parameters, including HD mode, dialyzer surface area, ultrafiltration goal, hypotension during HD, blood flow rate, activated partial thromboplastin time, and C-reactive protein. Multivariate regression was also conducted to explore the relationships among these parameters.

RESULTS

The mean RBC volume remaining in the extracorporeal blood circuit after HD was 1.6 ± 0.9 mL (mode: 1.0, range: 0.3-6.5 mL). When converted to whole blood volume per patient, the mean blood volume was 5.3 ± 3.0 mL (median: 4.1 mL, mode: 4.0 mL, range: 1.0-19.0 mL). Multivariate analysis identified the dialyzer surface area as the only significant determinant of residual RBC volume.

CONCLUSION

After HD, the remaining RBC volume in the extracorporeal blood circuit varies from 1.6 to 6.5 mL. When the RBC volume was converted to whole blood volume for each case, the blood loss ranged from 1.0 to 19.0 mL. Dialyzer surface area was the only significant determinant of residual RBC volume.

Utility of Global Hemostatic Assays in Patients with Bleeding Disorders of Unknown Cause

Bleeding disorder of unknown cause (BDUC) is a diagnosis of exclusion after exhaustive evaluation of plasmatic coagulation and platelet function. This review explores the utility of global hemostatic assays as confirmatory tests and in elucidating the pathophysiology of BDUC. Unlike traditional hemostatic tests that focus on coagulation factors, global assays are conducted both in plasma and also whole blood. These assays provide a more comprehensive understanding of the cell-based model of coagulation, aid in the identification of plasmatic factor abnormalities that may reduce hemostatic capacity, and allow for the assessment of impaired platelet-endothelial interactions under shear stress, as well as hyperfibrinolytic states. While clinical tests such as skin bleeding time and global assays such as PFA-100 exhibit limited diagnostic capacity, the role of viscoelastic testing in identifying hemostatic dysfunction in patients with BDUC remains unclear. Thrombin generation assays have shown variable results in BDUC patients; some studies demonstrate differences compared with healthy controls or reference values, whereas others question its clinical utility. Fibrinolysis assessment in vitro remains challenging, with studies employing euglobulin clot lysis time, plasma clot lysis time, and fluorogenic plasmin generation yielding inconclusive or conflicting results. Notably, recent studies suggest that microfluidic analysis unveils shear-dependent platelet function defects in BDUC patients, undetected by conventional platelet function assays. Overall, global assays might be helpful for exploring underlying hemostatic impairments, when conventional hemostatic laboratory tests yield no results. However, due to limited data and/or discrepant results, further research is needed to evaluate the utility of global assays as screening tools.

Biomechanical Analysis of Age-Dependent Changes in Fontan Power Loss

The hemodynamics in Fontan patients with single ventricles rely on favorable flow and energetics, especially in the absence of a subpulmonary ventricle. Age-related changes in energetics for extracardiac and lateral tunnel Fontan procedures are not well understood. Vorticity (VOR) and viscous dissipation rate (VDR) are two descriptors that can provide insights into flow dynamics and dissipative areas in Fontan pathways, potentially contributing to power loss. This study examined power loss and its correlation with spatio-temporal flow descriptors (vorticity and VDR). Data from 414 Fontan patients were used to establish a relationship between the superior vena cava (SVC) to inferior vena cava (IVC) flow ratio and age. Computational flow modeling was conducted for both extracardiac conduits (ECC, n = 16) and lateral tunnels (LT, n = 25) at different caval inflow ratios of 2, 1, and 0.5 that corresponded with ages 3, 8, and 15+. In both cohorts, vorticity and VDR correlated well with PL, but ECC cohort exhibited a slightly stronger correlation for PL-VOR (>0.83) and PL-VDR (>0.89) than that for LT cohort (>0.76 and > 0.77, respectively) at all ages. Our data also suggested that absolute and indexed PL increase (p < 0.02) non-linearly as caval inflow changes with age and are highly patient-specific. Comparison of indexed power loss between our ECC and LT cohort showed that while ECC had a slightly higher median PL for all 3 caval inflow ratio examined (3.3, 8.3, 15.3) as opposed to (2.7, 7.6, 14.8), these differences were statistically non-significant. Lastly, there was a consistent rise in pressure gradient across the TCPC with age-related increase in IVC flows for both ECC and LT Fontan patient cohort. Our study provided hemodynamic insights into Fontan energetics and how they are impacted by age-dependent change in caval inflow. This workflow may help assess the long-term sustainability of the Fontan circulation and inform the design of more efficient Fontan conduits.

Autophagy-enabled protein degradation: Key to platelet activation and ANGII production in patients with type 2 diabetes mellitus

Background

Type 2 diabetes mellitus (T2DM) presents a thrombotic environment, contributing to diabetic macroangiopathy and microangiopathy. In this study, the regulation of microthrombosis in T2DM was assessed.

Methods

Platelets from T2DM patients and healthy controls were analyzed using 4D label-free proteomics and bioinformatics. The role of autophagy in T2DM platelet activation and conversion of platelet-derived angiotensinogen (AGT) was investigated.

Results

The results showed that complement and coagulation cascades, platelet activation, metabolic pathways, endocytosis, autophagy, and other protein digestion-related pathways were enriched. The levels of the key protein AGT were increased in T2DM platelets. Chloroquine (CQ) inhibited ADP- or arachidonic acid (AA)-stimulated platelet aggregation and granule release in a dose-dependent manner, while the effects were less pronounced or even reversed for the proteasome inhibitor PYR-41 and the endocytosis inhibitor Pitstop 2. This indicated the dependence of platelet activation and the accompanying protein digestion on the autophagy-lysosome pathway. Mitophagy occurred in fresh T2DM platelets and ADP- or storage-stimulated platelets; mitophagy was inhibited by CQ. However, the mitophagy inhibitor Mdivi-1 failed to show effects similar to those of CQ. AGT, which could be transformed into ANGII in vitro by ADP-stimulated platelets, was upregulated in T2DM platelets and in MEG-01 cell-derived platelets cultured in a high-glucose medium. Finally, microthrombosis was alleviated as indicated by a reduction in the levels of red blood cells in the liver, spleen, heart, and kidney tissues of db/db mice treated with CQ or valsartan.

Conclusion

In platelets, macroautophagy promotes protein digestion, subsequently facilitating platelet activation, ANGII-mediated vasoconstriction, and microthrombosis. Our results suggested that lysosome is a promising therapeutic target for antithrombotic treatment in T2DM.

Parasagittal and Superior Sagittal Sinus Dural Arteriovenous Fistulas: Clinical Presentations, Imaging Characteristics, and Treatment Strategies

BACKGROUND AND PURPOSE

Parasagittal and superior sagittal sinus (SSS) dural arteriovenous fistulas (DAVFs) are often inappropriately classified. We explore the clinical presentations, imaging characteristics, and endovascular treatment strategies of these 2 DAVF subtypes.

MATERIALS AND METHODS

Clinical and imaging data of 19 patients with SSS or parasagittal sinus DAVFs who underwent endovascular treatment in our institution between 2017 and 2022 were retrospectively analyzed. The angiographic findings, endovascular treatment strategies, and angiographic outcomes were evaluated and recorded.

RESULTS

Among these 19 patients, 14 had a parasagittal DAVF, 4 had a SSS DAVF, and 1 patient had both parasagittal and SSS DAVF. Only 1 (1/19, 5.26%) patient presented with intracranial hemorrhage. For the parasagittal DAVF group, most of the shunts were located along the middle third of the SSS (12/15, 80%), on the dura in proximity with the junctional zone between the bridging vein and SSS (15/15, 100%), with ipsilateral cortical venous reflux (CVR) (15/15, 100%). For the SSS DAVF group, all 5 patients had shunting zone along the middle third of the SSS, on the sinus or parasinus wall, with bilateral CVR. Transarterial embolization, via the middle meningeal artery as the primary route of access, was the primary treatment approach in 95% of cases (19/20). Reflux of embolization material into the SSS was observed in 1 case (1/5, 20%) of SSS DAVF in which balloon sinus protection was not used during embolization.

CONCLUSIONS

Our study found that parasagittal DAVFs have shunting point(s) centered on the junctional zone of the bridging vein and the SSS with ipsilateral CVR, while SSS DAVFs have shunting point(s) centered on the sinus or parasinus wall with bilateral CVR. Transarterial embolization via the middle meningeal artery can be used as the primary treatment strategy in most cases. Balloon sinus protection during embolization is not necessary in cases of parasagittal DAVF with occluded or stenosed connection with the SSS but its use should be considered in cases of SSS DAVF with patent sinus.

Numerical simulation and in vitro experimental study of the hemodynamic performance of vena cava filters with helical forms

Inferior vena cava filter (IVCF) implantation is a common method of thrombus capture. By implanting a filter in the inferior vena cava (IVC), microemboli can be effectively blocked from entering the pulmonary circulation, thereby avoiding acute pulmonary embolism (PE). Inspired by the helical flow effect in the human arterial system, we propose a helical retrievable IVCF, which, due to the presence of a helical structure inducing a helical flow pattern of blood in the region near the IVCF, can effectively avoid the deposition of microemboli in the vicinity of the IVCF while promoting the cleavage of the captured thrombus clot. It also reduces the risk of IVCF dislodging and slipping in the vessel because its shape expands in the radial direction, allowing its distal end to fit closely to the IVC wall, and because its contact structure with the inner IVC wall is curved, increasing the contact area and reducing the risk of the vessel wall being punctured by the IVCF support structure. We used ANSYS 2023 software to conduct unidirectional fluid-structure coupling simulation of four different forms of IVCF, combined with microthrombus capture experiments in vitro, to explore the impact of these four forms of IVCF on blood flow patterns and to evaluate the risk of IVCF perforation and IVCF dislocation. It can be seen from the numerical simulation results that the helical structure does have the function of inducing blood flow to undergo helical flow dynamics, and the increase in wall shear stress (WSS) brought about by this function can improve the situation of thrombosis accumulation to a certain extent. Meanwhile, the placement of IVCF will change the flow state of blood flow and lead to the deformation of blood vessels. In in vitro experiments, we found that the density of the helical support rod is a key factor affecting the thrombus trapping efficiency, and in addition, the contact area between the IVCF and the vessel wall has a major influence on the risk of IVCF displacement.

Sutureless vascular anastomotic approaches and their potential impacts

Sutureless anastomotic devices present several advantages over traditional suture anastomosis, including expanded global access to microvascular surgery, shorter operation and ischemic times, and reduced costs. However, their adaptation for arterial use remains a challenge. This review aims to provide a comprehensive overview of sutureless anastomotic approaches that are either FDA-approved or under investigation. These approaches include extraluminal couplers, intraluminal devices, and methods assisted by lasers or vacuums, with a particular emphasis on tissue adhesives. We analyze these devices for artery compatibility, material composition, potential for intimal damage, risks of thrombosis and restenosis, and complications arising from their deployment and maintenance. Additionally, we discuss the challenges faced in the development and clinical application of sutureless anastomotic techniques. Ideally, a sutureless anastomotic device or technique should eliminate the need for vessel eversion, mitigate thrombosis through either biodegradation or the release of antithrombotic drugs, and be easily deployable for broad use. The transformative potential of sutureless anastomotic approaches in microvascular surgery highlights the necessity for ongoing innovation to expand their applications and maximize their benefits.

Computational Pulsatile Flow and Efficiency Analysis of Biocompatible Microfluidic Artificial Lungs for Different Fiber Configurations

Average-sized microfluidic artificial lungs consisting of rows and columns of fiber bundles with different column to row aspect ratios (AR) are numerically analyzed for flow characteristics, maximum gas transfer performance, minimum pressure drop, and proper wall shear stress (WSS) values in terms of biocompatibility. The flow is fully laminar and assumed to be incompressible and Newtonian. The transport analysis is performed using a combined convection-diffusion model, and the numerical simulations are carried out with the finite element method. The inlet volumetric flow is modeled as a sinusoidal wave function to simulate the cardiac cycle and its effect on the device performance. The model is first validated with experimental studies in steady-state condition and compared with existing correlations for transient conditions. Then, the validated model is used for a parametric study in both steady and pulsatile flow conditions. The results show that increasing the aspect ratio in fiber configuration leads to converging gas transfer, higher pressure drop, and higher WSS. While determining the optimum configuration, the acceptable shear stress levels play a decisive role to ensure biocompatibility. Also, it is observed that the steady analysis underestimates the gas transfer for higher aspect ratios.

INVESTIGATING THE RELATIONSHIP BETWEEN BLEEDING, CLOTTING, AND COAGULOPATHY DURING AUTOMATED PARTIAL REBOA STRATEGIES IN A HIGHLY LETHAL PORCINE HEMORRHAGE MODEL

ABSTRACT

Background: Death due to hemorrhagic shock, particularly, noncompressible truncal hemorrhage, remains one of the leading causes of potentially preventable deaths. Automated partial and intermittent resuscitative endovascular balloon occlusion of the aorta (i.e., pREBOA and iREBOA, respectively) are lifesaving endovascular strategies aimed to achieve quick hemostatic control while mitigating distal ischemia. In iREBOA, the balloon is titrated from full occlusion to no occlusion intermittently, whereas in pREBOA, a partial occlusion is maintained. Therefore, these two interventions impose different hemodynamic conditions, which may impact coagulation and the endothelial glycocalyx layer. In this study, we aimed to characterize the clotting kinetics and coagulopathy associated with iREBOA and pREBOA, using thromboelastography (TEG). We hypothesized that iREBOA would be associated with a more hypercoagulopathic response compared with pREBOA due to more oscillatory flow. Methods: Yorkshire swine (n = 8/group) were subjected to an uncontrolled hemorrhage by liver transection, followed by 90 min of automated pREBOA, iREBOA, or no balloon support (control). Hemodynamic parameters were continuously recorded, and blood samples were serially collected during the experiment (i.e., eight key time points: baseline (BL), T0, T10, T30, T60, T90, T120, T210 min). Citrated kaolin heparinase assays were run on a TEG 5000 (Haemonetics, Niles, IL). General linear mixed models were employed to compare differences in TEG parameters between groups and over time using STATA (v17; College Station, TX), while adjusting for sex and weight. Results: As expected, iREBOA was associated with more oscillations in proximal pressure (and greater magnitudes of peak pressure) because of the intermittent periods of full aortic occlusion and complete balloon deflation, compared to pREBOA. Despite these differences in acute hemodynamics, there were no significant differences in any of the TEG parameters between the iREBOA and pREBOA groups. However, animals in both groups experienced a significant reduction in clotting times (R time: P < 0.001; K time: P < 0.001) and clot strength (MA: P = 0.01; G: P = 0.02) over the duration of the experiment. Conclusions: Despite observing acute differences in peak proximal pressures between the iREBOA and pREBOA groups, we did not observe any significant differences in TEG parameters between iREBOA and pREBOA. The changes in TEG profiles were significant over time, indicating that a severe hemorrhage followed by both pREBOA and iREBOA can result in faster clotting reaction times (i.e., R times). Nevertheless, when considering the significant reduction in transfusion requirements and more stable hemodynamic response in the pREBOA group, there may be some evidence favoring pREBOA usage over iREBOA.

Clot Accumulation in 3D Microfluidic Bifurcating Microvasculature Network

The microvasculature, which makes up the majority of the cardiovascular system, plays a crucial role in the process of thrombosis, with the pathological formation of blood clots inside blood vessels. Since blood microflow conditions significantly influence platelet activation and thrombosis, accurately mimicking the structure of bifurcating microvascular networks and emulating local physiological blood flow conditions are valuable for understanding blood clot formation. In this work, we present an in vitro model for blood clotting in microvessels, focusing on 3D bifurcations that align with Murray's law, which guides vascular networks by maintaining a constant wall shear rate throughout. Using these models, we demonstrate that microvascular bifurcations act as sites facilitating thrombus formation compared to straight models. Additionally, by culturing endothelial cells on the luminal surfaces of the models, we show the potential of using our in vitro platforms to recapitulate the initial clotting in diseases involving endothelial dysfunction, such as Thrombotic Thrombocytopenic Purpura.

A double-edged sword: The complex interplay between engineered nanoparticles and platelets

Nanoparticles (NP) play a crucial role in nanomedicine, serving as carriers for localized therapeutics to allow for precise drug delivery to specific disease sites and conditions. When injected systemically, NP can directly interact with various blood cell types, most critically with circulating platelets. Hence, the potential activation/inhibition of platelets following NP exposure must be evaluated a priori due to possible debilitating outcomes. In recent years, various studies have helped resolve the physicochemical parameters that influence platelet-NP interactions, and either emphasize nanoparticles' therapeutic role such as to augment hemostasis or to inhibit thrombus formation, or conversely map their potential undesired side effects upon injection. In the present review, we discuss some of the main effects of several key NP types including polymeric, ceramic, silica, dendrimers and metallic NPs on platelets, with a focus on the physicochemical parameters that can dictate these effects and modulate the therapeutic potential of the NP. Despite the scientific and clinical significance of understanding Platelet-NP interactions, there is a significant knowledge gap in the field and a critical need for further investigation. Moreover, improved guidelines and research methodologies need to be developed and implemented. Our outlook includes the use of biomimetic in vitro models to investigate these complex interactions under both healthy physiological and disease conditions.

Whole Blood Viscosity and Cerebral Blood Flow in Acute Ischemic Stroke

Existing effective treatments for ischemic stroke restore blood supply to the ischemic region using thrombolysis or mechanical removal of clot. However, it is increasingly recognized that successful removal of occlusive thrombus from the large artery-recanalization, may not always be accompanied by successful restoration of blood flow to the downstream tissues-reperfusion. Ultimately, brain tissue survival depends on cerebral perfusion, and a functioning microcirculation. Because capillary diameter is often equal to or smaller than an erythrocyte, microcirculation is largely dependent on erythrocyte rheological (hemorheological) factors such as whole blood viscosity (WBV). Several studies in the past have demonstrated elevated WBV in stroke compared with healthy controls. Also, elevated WBV has shown to be an independent risk factor for stroke. Elevated WBV leads to endothelial dysfunction, decreases nitric oxide-dependent flow-mediated vasodilation, and promotes hemostatic alterations/thrombosis, all leading to microcirculation sludging. Compromised microcirculation further leads to decreased cerebral perfusion. Hence, modulating WBV through pharmacological agents might be beneficial to improve cerebral perfusion in stroke. This review discusses the effect of elevated WBV on endothelial function, hemostatic alterations, and thrombosis leading to reduced cerebral perfusion in stroke.

Water content for clot composition prediction in acute ischemic stroke

BACKGROUND

Mechanical thrombectomy (MT) has become the gold standard care for treating acute ischemic stroke (AIS) due to large vessel occlusion. Emerging evidence suggests that understanding the composition of clots prior to intervention could be useful for the selection of neuroendovascular techniques, potentially improving the efficacy of treatments. However, current imaging modalities lack the ability to distinguish clot composition accurately and reliably. Since water content can influence signal intensity on CT and MRI scans, its assessment may provide indirect clues about clot composition. This study aimed to elucidate the correlation between water content and clot composition using human clots retrieved from stroke patients and experimentally generated ovine clots.

MATERIALS AND METHODS

This study involved an analysis of ten clots retrieved from patients with AIS undergoing MT. Additionally, we created ten red blood cells (RBC)-rich and ten fibrin-rich ovine blood clots, which were placed in a human intracranial vascular model under realistic flow conditions. The water content and compositions of these clots were evaluated, and linear regression analyses were performed to determine the relationship between clot composition and water content.

RESULTS

The regression analysis in human stroke clots revealed a significant negative association between RBC concentration and water content. We also observed a positive correlation between water content and both fibrin and platelets in ovine blood clots. Conclusion.

In silico analysis of embolism in cerebral arteries using fluid-structure interaction method

Ischemic stroke, particularly embolic stroke, stands as a significant global contributor to mortality and long-term disabilities. This paper presents a comprehensive simulation of emboli motion through the middle cerebral artery (MCA), a prevalent site for embolic stroke. Our patient-specific computational model integrates major branches of the middle cerebral artery reconstructed from magnetic resonance angiography images, pulsatile flow dynamics, and emboli of varying geometries, sizes, and material properties. The fluid-structure interactions method is employed to simulate deformable emboli motion through the middle cerebral artery, allowing observation of hemodynamic changes in artery branches upon embolus entry. We investigated the impact of embolus presence on shear stress magnitude on artery walls, analyzed the effects of embolus material properties and geometries on embolus trajectory and motion dynamics within the middle cerebral artery. Additionally, we evaluated the non-Newtonian behavior of blood, comparing it with Newtonian blood behavior. Our findings highlight that embolus geometry significantly influences trajectory, motion patterns, and hemodynamics within middle cerebral artery branches. Emboli with visco-hyperelastic material properties experienced higher stresses upon collision with artery walls compared to those with hyperelastic properties. Furthermore, considering blood as a non-Newtonian fluid had notable effects on emboli stresses and trajectories within the artery, particularly during collisions. Notably, the maximum von Mises stress experienced in our study was 21.83 kPa, suggesting a very low probability of emboli breaking during movement, impact, and after coming to a stop. However, in certain situations, the magnitude of shear stress on them exceeded 1 kPa, increasing the likelihood of cracking and disintegration. These results serve as an initial step in anticipating critical clinical conditions arising from arterial embolism in the middle cerebral artery. They provide insights into the biomechanical parameters influencing embolism, contributing to improved clinical decision-making for stroke management.

Design, development and preliminary assessment in a porcine model of a novel peripheral intravenous catheter aimed at reducing early failure rates

BACKGROUND

Peripheral intravenous catheters (PIVCs) are the most commonly used invasive medical device, yet despite best efforts by end-users, PIVCs experience unacceptably high early failure rates. We aimed to design a new PIVC that reduces the early failure rate of in-dwelling PIVCs and we conducted preliminary tests to assess its efficacy and safety in a porcine model of intravenous access.

METHODS

We used computer-aided design and simulation to create a PIVC with a ramped tip geometry, which directs the infused fluid away from the vein wall; we called the design the FloRamp™. We created FloRamp prototypes (test device) and tested them against a market-leading device (BD Insyte™; control device) in a highly-controlled setting with five insertion sites per device in four pigs. We measured resistance to infusion and visual infusion phlebitis (VIP) every 6 h and terminated the experiment at 48 h. Veins were harvested for histology and seven pathological markers were assessed.

RESULTS

Computer simulations showed that the optimum FloRamp tip reduced maximum endothelial shear stress by 60%, from 12.7 Pa to 5.1 Pa, compared to a typical PIVC tip and improved the infusion dynamics of saline in the blood stream. In the animal study, we found that 2/5 of the control devices were occluded after 24 h, whereas all test devices remained patent and functional. The FloRamp created less resistance to infusion (0.73 ± 0.81 vs 0.47 ± 0.50, p = 0.06) and lower VIP scores (0.60 ± 0.93 vs 0.31 ± 0.70, p = 0.09) than the control device, although neither findings were significantly different. Histopathology revealed that 5/7 of the assessed markers were lower in veins with the FloRamp.

CONCLUSIONS

Herein we report preliminary assessment of a novel PIVC design, which could be advantageous in clinical settings through decreased device occlusion and reduced early failure rates.

Extracorporeal Blood Treatment Using Functional Magnetic Nanoclusters Mitigates Organ Dysfunction of Sepsis in Swine

Mitigating sepsis-induced severe organ dysfunction with magnetic nanoparticles has shown remarkable advances in extracorporeal blood treatment. Nevertheless, treating large septic animals remains challenging due to insufficient magnetic separation at rapid blood flow rates (>6 L h-1) and limited incubation time in an extracorporeal circuit. Herein, superparamagnetic nanoclusters (SPNCs) coated with red blood cell (RBC) membranes are developed, which promptly capture and magnetically separate a wide range of pathogens at high blood flow rates in a swine sepsis model. The SPNCs exhibited an ultranarrow size distribution of clustered iron oxide nanocrystals and exceptionally high saturation magnetization (≈ 90 emu g-1) close to that of bulk magnetite. It is also revealed that CD47 on the RBCs allows the RBC-SPNCs to remain at a consistent concentration in the blood by evading innate immunity. The uniform size distribution of the RBC-SPNCs greatly enhances their effectiveness in eradicating various pathogenic materials in extracorporeal blood. The use of RBC-SPNCs for extracorporeal treatment of swine infected with multidrug-resistant E. coli is validated and found that severe bacteremic sepsis-induced organ dysfunction is significantly mitigated after 12 h. The findings highlight the potential application of RBC-SPNCs for extracorporeal therapy of severe sepsis in large animal models and potentially humans.

Patient-specific tissue engineered vascular graft for aortic arch reconstruction

Objectives

The complexity of aortic arch reconstruction due to diverse 3-dimensional geometrical abnormalities is a major challenge. This study introduces 3-dimensional printed tissue-engineered vascular grafts, which can fit patient-specific dimensions, optimize hemodynamics, exhibit antithrombotic and anti-infective properties, and accommodate growth.

Methods

We procured cardiac magnetic resonance imaging with 4-dimensional flow for native porcine anatomy (n = 10), from which we designed tissue-engineered vascular grafts for the distal aortic arch, 4 weeks before surgery. An optimal shape of the curved vascular graft was designed using computer-aided design informed by computational fluid dynamics analysis. Grafts were manufactured and implanted into the distal aortic arch of porcine models, and postoperative cardiac magnetic resonance imaging data were collected. Pre- and postimplant hemodynamic data and histology were analyzed.

Results

Postoperative magnetic resonance imaging of all pigs with 1:1 ratio of polycaprolactone and poly-L-lactide-co-ε-caprolactone demonstrated no specific dilatation or stenosis of the graft, revealing a positive growth trend in the graft area from the day after surgery to 3 months later, with maintaining a similar shape. The peak wall shear stress of the polycaprolactone/poly-L-lactide-co-ε-caprolactone graft portion did not change significantly between the day after surgery and 3 months later. Immunohistochemistry showed endothelization and smooth muscle layer formation without calcification of the polycaprolactone/poly-L-lactide-co-ε-caprolactone graft.

Conclusions

Our patient-specific polycaprolactone/poly-L-lactide-co-ε-caprolactone tissue-engineered vascular grafts demonstrated optimal anatomical fit maintaining ideal hemodynamics and neotissue formation in a porcine model. This study provides a proof of concept of patient-specific tissue-engineered vascular grafts for aortic arch reconstruction.

Virtual Planning and Patient-Specific Graft Design for Aortic Repairs

PURPOSE

Patients presenting with coarctation of the aorta (CoA) may also suffer from co-existing transverse arch hypoplasia (TAH). Depending on the risks associated with the surgery and the severity of TAH, clinicians may decide to repair only CoA, and monitor the TAH to see if it improves as the patient grows. While acutely successful, eventually hemodynamics may become suboptimal if TAH is left untreated. The objective of this work aims to develop a patient-specific surgical planning framework for predicting and assessing postoperative outcomes of simple CoA repair and comprehensive repair of CoA and TAH.

METHODS

The surgical planning framework consisted of virtual clamp placement, stenosis resection, and design and optimization of patient-specific aortic grafts that involved geometrical modeling of the graft and computational fluid dynamics (CFD) simulation for evaluating various surgical plans. Time-dependent CFD simulations were performed using Windkessel boundary conditions at the outlets that were obtained from patient-specific non-invasive pressure and flow data to predict hemodynamics before and after the virtual repairs. We applied the proposed framework to investigate optimal repairs for six patients (n = 6) diagnosed with both CoA and TAH. Design optimization was performed by creating a combination of a tubular graft and a waterslide patch to reconstruct the aortic arch. The surfaces of the designed graft were parameterized to optimize the shape.

RESULTS

Peak systolic pressure drop (PSPD) and time-averaged wall shear stress (TAWSS) were used as performance metrics to evaluate surgical outcomes of various graft designs and implantation. The average PSPD improvements were 28% and 44% after the isolated CoA repair and comprehensive repair, respectively. Maximum values of TAWSS were decreased by 60% after CoA repair and further improved by 22% after the comprehensive repair. The oscillatory shear index was calculated and the values were confirmed to be in the normal range after the repairs.

CONCLUSION

The results showed that the comprehensive repair outperforms the simple CoA repair and may be more advantageous in the long term in some patients. We demonstrated that the surgical planning and patient-specific flow simulations could potentially affect the selection and outcomes of aorta repairs.

Fundamental considerations for designing endothelialized in vitro models of thrombosis

Endothelialized in vitro models for cardiovascular disease have contributed greatly to our current understanding of the complex molecular mechanisms underlying thrombosis. To further elucidate these mechanisms, it is important to consider which fundamental aspects to incorporate into an in vitro model. In this review, we will focus on the design of in vitro endothelialized models of thrombosis. Expanding our understanding of the relation and interplay between the different pathways involved will rely in part on complex models that incorporate endothelial cells, blood, the extracellular matrix, and flow. Importantly, the use of tissue-specific endothelial cells will help in understanding the heterogeneity in thrombotic responses between different vascular beds. The dynamic and complex responses of endothelial cells to different shear rates underlines the importance of incorporating appropriate shear in in vitro models. Alterations in vascular extracellular matrix composition, availability of bioactive molecules, and gradients in concentration and composition of these molecules can all regulate the function of both endothelial cells and perivascular cells. Factors modulating these elements in in vitro models should therefore be considered carefully depending on the research question at hand. As the complexity of in vitro models increases, so can the variability. A bottom-up approach to designing such models will remain an important tool for researchers studying thrombosis. As new techniques are continuously being developed and new pathways are brought to light, research question-dependent considerations will have to be made regarding what aspects of thrombosis to include in in vitro models.

Flow characterization of Maquet and Bio-Medicus multi-stage drainage cannulae during venoarterial extracorporeal membrane oxygenation

BACKGROUND

Drainage cannulae extract blood from a patient during venoarterial extracorporeal membrane oxygenation (VA ECMO), a treatment that temporarily supports patients undergoing severe heart and/or lung dysfunction. Currently, the two most commonly used multi-stage drainage cannulae are manufactured by Maquet and Bio-Medicus, but their designs vary in many aspects which impacts the generated flow dynamics. Therefore, this study aimed to use computational fluid dynamics (CFD) to explore the flow characteristics of the aforementioned cannulae and their impact on complications such as thrombosis.

METHODS

The Maquet and Bio-Medicus cannulae were 3D modelled within a patient-specific geometry of the venous vasculature taken from a computed tomography scan of a patient undergoing VA ECMO. A drainage flow rate of 4 L/min was assigned to each cannula. Lastly, a stress blended eddy simulation turbulence model was employed to resolve bulk flow turbulence.

RESULTS

The proximal row of side holes in both cannulae generated high intensity counter-rotating vortices, thus generating supraphysiological shear. These proximal rows were also responsible for the majority of flow extraction in both cannulae (>1.6 L/min). Despite identical simulation settings, each cannulae had differing impacts on global flow dynamics. For instance, the Bio-Medicus model produced a total stagnant blood volume of 25.6 ml, compared to 17.8 ml the Maquet cannula, thereby increasing the risk of thrombosis.

CONCLUSIONS

Overall, our results demonstrate that differences in design clearly impact flow dynamics and risk of complications. Therefore, further work in optimizing cannula design may be beneficial to prevent harmful flow characteristics.

A microfluidic platform integrating functional vascularized organoids-on-chip

The development of vascular networks in microfluidic chips is crucial for the long-term culture of three-dimensional cell aggregates such as spheroids, organoids, tumoroids, or tissue explants. Despite rapid advancement in microvascular network systems and organoid technologies, vascularizing organoids-on-chips remains a challenge in tissue engineering. Most existing microfluidic devices poorly reflect the complexity of in vivo flows and require complex technical set-ups. Considering these constraints, we develop a platform to establish and monitor the formation of endothelial networks around mesenchymal and pancreatic islet spheroids, as well as blood vessel organoids generated from pluripotent stem cells, cultured for up to 30 days on-chip. We show that these networks establish functional connections with the endothelium-rich spheroids and vascular organoids, as they successfully provide intravascular perfusion to these structures. We find that organoid growth, maturation, and function are enhanced when cultured on-chip using our vascularization method. This microphysiological system represents a viable organ-on-chip model to vascularize diverse biological 3D tissues and sets the stage to establish organoid perfusions using advanced microfluidics.

Flow affects the structural and mechanical properties of the fibrin network in plasma clots

The fibrin network is one of the main components of thrombi. Altered fibrin network properties are known to influence the development and progression of thrombotic disorders, at least partly through effects on the mechanical stability of fibrin. Most studies investigating the role of fibrin in thrombus properties prepare clots under static conditions, missing the influence of blood flow which is present in vivo. In this study, plasma clots in the presence and absence of flow were prepared inside a Chandler loop. Recitrated plasma from healthy donors were spun at 0 and 30 RPM. The clot structure was characterized using scanning electron microscopy and confocal microscopy and correlated with the stiffness measured by unconfined compression testing. We quantified fibrin fiber density, pore size, and fiber thickness and bulk stiffness at low and high strain values. Clots formed under flow had thinner fibrin fibers, smaller pores, and a denser fibrin network with higher stiffness values compared to clots formed in absence of flow. Our findings indicate that fluid flow is an essential factor to consider when developing physiologically relevant in vitro thrombus models used in researching thrombectomy outcomes or risk of embolization.

A streamlined controlled-expansion covered tapered stent for TIPS in the treatment of PHT

Transjugular intrahepatic portosystemic shunt (TIPS) relieves cirrhotic complications by reducing portacaval pressure gradient (PCG), but it lacks precision in achieving a targeted post-TIPS PCG simply through diameter adjustment of equal diameter stents. This study aimed to present a controlled-expansion, streamlined, and covered tapered stent, and examined its effects on pressure reduction compared with equal- diameter stents. Twenty-four patients who underwent standardized 8-mm stent TIPS implantation at West China Hospital from December 2017 to February 2021 were included in the current study. Virtual equal-diameter stent graft with different diameter and streamlined tapered stents were created in the post-TIPS 3-dimentional models reconstructed based on computed tomography angiography data. The numerical simulation showed that only two patients achieved targeted post-TIPS PCG consistent with the clinical invasive measurement. When 6-mm and 10-mm equal-diameter stents were employed, simulated post-TIPS PCGs for most patients remained outside the safe range, and recirculating flow was observed at the stent-portal vein anastomosis. In contrast, the use of the new streamlined taper stent resulted in post-TIPS PCGs within the 10-12 mmHg range for 17 out of 24 patients, with no recirculating flow observed at the anastomotic sites. In conclusion, the streamlined tapered stent could pose an effective solution to the problem that the big jump depressurization between two different equal-diameter stents and it would improve the hemodynamics in the region near the PV-stent anchorage. Therefore, the streamlined tapered stent may present a superior alternative for TIPS procedure.

High blood viscosity in acute ischemic stroke

Background

The changes in blood viscosity can influence the shear stress at the vessel wall, but there is limited evidence regarding the impact on thrombogenesis and acute stroke. We aimed to investigate the effect of blood viscosity on stroke and the clinical utility of blood viscosity measurements obtained immediately upon hospital arrival.

Methods

Patients with suspected stroke visiting the hospital within 24 h of the last known well time were enrolled. Point-of-care testing was used to obtain blood viscosity measurements before intravenous fluid infusion. Blood viscosity was measured as the reactive torque generated at three oscillatory frequencies (1, 5, and 10 rad/sec). Blood viscosity results were compared among patients with ischemic stroke, hemorrhagic stroke, and stroke mimics diagnosed as other than stroke.

Results

Among 112 enrolled patients, blood viscosity measurements were accomplished within 2.4 ± 1.3 min of vessel puncture. At an oscillatory frequency of 10 rad/sec, blood viscosity differed significantly between the ischemic stroke (24.2 ± 4.9 centipoise, cP) and stroke mimic groups (17.8 ± 6.5 cP, p < 0.001). This finding was consistent at different oscillatory frequencies (134.2 ± 46.3 vs. 102.4 ± 47.2 at 1 rad/sec and 39.2 ± 11.5 vs. 30.4 ± 12.4 at 5 rad/sec, Ps < 0.001), suggesting a relationship between decreases in viscosity and shear rate. The area under the receiver operating curve for differentiating cases of stroke from stroke mimic was 0.79 (95% confidence interval, 0.69-0.88).

Conclusion

Patients with ischemic stroke exhibit increases in whole blood viscosity, suggesting that blood viscosity measurements can aid in differentiating ischemic stroke from other diseases.

Effect of molar mass and alkyl chain length on the surface properties and biocompatibility of poly(alkylene terephthalate)s for potential cardiovascular applications

Cardiovascular diseases are the leading cause of death worldwide. Treatments for occluded arteries include balloon angioplasty with or without stenting and bypass grafting surgery. Poly(ethylene terephthalate) is frequently used as a vascular graft material, but its high stiffness leads to compliance mismatch with the human blood vessels, resulting in altered hemodynamics, thrombus formation and graft failure. Poly(alkylene terephthalate)s (PATs) with longer alkyl chain lengths hold great potential for improving the compliance. In this work, the effect of the polymer molar mass and the alkyl chain length on the surface roughness and wettability of spin-coated PAT films was investigated, as well as the endothelial cell adhesion and proliferation on these samples. We found that surface roughness generally increases with increasing molar mass and alkyl chain length, while no trend for the wettability could be observed. All investigated PATs are non-cytotoxic and support endothelial cell adhesion and growth. For some PATs, the endothelial cells even reorganized into a tubular-like structure, suggesting angiogenic maturation. In conclusion, this research demonstrates the biocompatibility of PATs and their potential to be applied as materials serving cardiovascular applications.

Hemodynamics of different configurations of the left subclavian artery parallel stent graft for thoracic endovascular aortic repair

BACKGROUND AND OBJECTIVE

Parallel (chimney and periscope) graft technique is an effective approach for left subclavian artery (LSA) reconstruction in patients treated by thoracic endovascular aortic repair (TEVAR) for the inadequate landing zone. However, certain stent graft (SG) configurations may promote thrombosis and reduce distal blood flow, increasing risks of cerebral infarction and reintervention.

METHODS

In this paper, we first attempt to systematically evaluate the hemodynamic performances of different parallel graft techniques as potential determinants of complication risks. Based on the patient-specific 3D aortic geometry undergoing parallel graft technique, fifteen models in total for five kinds of LSA branched SG configurations (Forward, Backward, Extended, Elliptical and Periscopic) were designed virtually, and the hemodynamic discrepancies between them were analyzed by computational fluid dynamics.

RESULTS

Results show that flow rate of patients undergoing periscope technique reduces by half compared with chimney technique, suggesting that periscope SG may cause more serious flow obstruction to LSA, leading to stroke. For chimney stent structure, the extension length 0has little influence on energy loss and other parameters. Conversely, hemodynamic differences between the retrograde curvature and the antegrade curvature are significant (time average WSS: 47.07%), so the retrograde curvature might prompt SG displacement. Furthermore, the flatter chimney SG induces more aggressive hemodynamic forces, among which the difference of the maximum WSS between the flatter SG and nearly round SG reaches 65.56%, leading to the greater risk of vascular wall damage.

CONCLUSIONS

Results obtained might provide suggestions for physicians to formulate appropriate parallel graft technique schemes in TEVAR.

The effect of splenic vein diameter on the diagnosis of portal vein thrombosis

BACKGROUND

It was still controversial that whether the increase of splenic vein (SV) diameter increased the risk of portal vein thrombosis (PVT), which was a severe disease with high mortality, in the clinic.

PURPOSES

This study, using computational fluid dynamics method, aimed to investigate how the increase of SV diameter affects the portal vein hemodynamics under different anatomical and geometric features of the portal venous system, thus how it induced to PVT.

METHODS

The ideal models of the portal system, including different anatomical structures according to the location of left gastric vein (LGV) and inferior mesenteric vein (IMV), and different geometric morphological parameters models were established to carry out numerical simulation in this study. In addition, the morphological parameters of real patients were measured to verify the numerical simulation results.

RESULTS

First, the wall shear stress (WSS) and helicity intensity, which were closely related to the occurrence of thrombosis, gradually decreased with the increase of SV diameter in all models. However, the degree of decrease was bigger in following models: (1) the models with LGV and IMV linking to SV compared with them linking to PV; (2) the models with big angle of PV and SV compared with small angle. In addition, the morbidity of PVT was higher when LGV and IMV linked to SV rather than them linked to PV in the real patients. Moreover, the angle of PV and SV was also different between PVT and non-PVT patients (125.53° ± 16.90° vs. 115.03° ± 16.10°, p = 0.01).

CONCLUSION

Whether the increase of SV diameter will result in PVT is depended on the anatomical structure of portal system and the angle between PV and SV, this is also the reason leading to the clinical controversy that the increase of SV diameter is the risk factor of PVT.

The Relationship Between TIMI Flow and MAPH Score in Patients Undergoing Primary Percutaneous Coronary Intervention for STEMI

The MAPH (mean platelet volume, age, total protein and hematocrit) score is a newly developed simple scoring system for patients with STEMI that has been associated with satisfactory predictive values to determine thrombus burden in STEMI patients. Therefore, the aim of our study was to determine the relationship between the MAPH risk score and TIMI flow in patients with STEMI.The study included 260 patients who underwent primary percutaneous coronary intervention between December 2019 to July 2022, and had TIMI 0 flow in the responsible coronary artery due to STEMI. According to the TIMI flow score after stent implantation, the patients were classified into either the no-reflow group (n = 59) or the normal flow group (n = 201). In order to calculate the MAPH score, ROC analysis was performed to find the cutoff point for each component of the MAPH score. MAPH scores were calculated (MPV + Age + Protein + Hematocrit) for both groups. Our study was a retrospective, observational study.In the multivariable regression analysis, the MAPH score (OR: 0.567; 95%CI: 0.330-0.973, P = 0.04) and glycoprotein IIb/IIIa inhibitors (OR: 0.249; 95%CI: 0.129-0.483, P < 0.001) were parameters found to be independent predictors of TIMI flow. An MAPH score value > 2.5 predicted the presence of low TIMI coronary flow in patients with STEMI, with 78% specificity and 45% sensitivity (ROC area under curve: 0.691, 95% CI: 0.617-0.766, P < 0.001).The MAPH risk score is simple, inexpensive, and quick to calculate. A high MAPH score may be an indicator of coronary no-reflow in patients with STEMI.

Prevention of cardiac surgery-associated acute kidney injury: a systematic review and meta-analysis of non-pharmacological interventions

BACKGROUND

Cardiac surgery-associated acute kidney injury (CSA-AKI) is frequent. While two network meta-analyses assessed the impact of pharmacological interventions to prevent CSA-AKI, none focused on non-pharmacological interventions. We aim to assess the effectiveness of non-pharmacological interventions to reduce the incidence of CSA-AKI.

METHODS

We searched PubMed, Embase, Central and clinical trial registries from January 1, 2004 (first consensus definition of AKI) to July 1, 2023. Additionally, we conducted manual screening of abstracts of major anesthesia and intensive care conferences over the last 5 years and reference lists of relevant studies. We selected all randomized controlled trials (RCTs) assessing a non-pharmacological intervention to reduce the incidence of CSA-AKI, without language restriction. We excluded RCTs of heart transplantation or involving a pediatric population. The primary outcome variable was CSA-AKI. Two reviewers independently identified trials, extracted data and assessed risk of bias. Random-effects meta-analyses were conducted to calculate risk ratios (RRs) with 95% confidence intervals (CIs). We used the Grading of Recommendations Assessment, Development, and Evaluation to assess the quality of evidence.

RESULTS

We included 86 trials (25,855 patients) evaluating 10 non-pharmacological interventions to reduce the incidence of CSA-AKI. No intervention had high-quality evidence to reduce CSA-AKI. Two interventions were associated with a significant reduction in CSA-AKI incidence, with moderate quality of evidence: goal-directed perfusion (RR, 0.55 [95% CI 0.40-0.76], I2 = 0%; Phet = 0.44) and remote ischemic preconditioning (RR, 0.86 [0.78-0.95]; I2 = 23%; Phet = 0.07). Pulsatile flow during cardiopulmonary bypass was associated with a significant reduction in CSA-AKI incidence but with very low quality of evidence (RR = 0.69 [0.48; 0.99]; I2 = 53%; Phet < 0.01). We found high quality of evidence for lack of effect of restrictive transfusion strategy (RR, 1.02 [95% CI 0.92; 1.12; Phet = 0.67; I2 = 3%) and tight glycemic control (RR, 0.86 [95% CI 0.55; 1.35]; Phet = 0.25; I2 = 26%).

CONCLUSIONS

Two non-pharmacological interventions are likely to reduce CSA-AKI incidence, with moderate quality of evidence: goal-directed perfusion and remote ischemic preconditioning.

Hemodynamics of thrombus formation in intracranial aneurysms: An in silico observational study

How prevalent is spontaneous thrombosis in a population containing all sizes of intracranial aneurysms? How can we calibrate computational models of thrombosis based on published data? How does spontaneous thrombosis differ in normo- and hypertensive subjects? We address the first question through a thorough analysis of published datasets that provide spontaneous thrombosis rates across different aneurysm characteristics. This analysis provides data for a subgroup of the general population of aneurysms, namely, those of large and giant size (>10 mm). Based on these observed spontaneous thrombosis rates, our computational modeling platform enables the first in silico observational study of spontaneous thrombosis prevalence across a broader set of aneurysm phenotypes. We generate 109 virtual patients and use a novel approach to calibrate two trigger thresholds: residence time and shear rate, thus addressing the second question. We then address the third question by utilizing this calibrated model to provide new insight into the effects of hypertension on spontaneous thrombosis. We demonstrate how a mechanistic thrombosis model calibrated on an intracranial aneurysm cohort can help estimate spontaneous thrombosis prevalence in a broader aneurysm population. This study is enabled through a fully automatic multi-scale modeling pipeline. We use the clinical spontaneous thrombosis data as an indirect population-level validation of a complex computational modeling framework. Furthermore, our framework allows exploration of the influence of hypertension in spontaneous thrombosis. This lays the foundation for in silico clinical trials of cerebrovascular devices in high-risk populations, e.g., assessing the performance of flow diverters in aneurysms for hypertensive patients.

Validity of Customized Branched Tissue Engineered Vascular Graft in a Porcine Model

Background

Patient-specific, 3-dimensional printed, tissue engineered vascular grafts (3DTEVGs) are manufactured to optimize hemodynamic performance and to accommodate growth. We evaluate growth outcomes of 3DTEVGs compared with standard grafts for pulmonary artery reconstruction in porcine models.

Methods

Magnetic resonance imaging (MRI) with 4-dimensional flow data was acquired in porcine models (n = 8). 3DTEVGs guided in design by computational flow dynamics were implanted (n = 4), with polytetrafluorethylene grafts used as controls (n = 4). Postoperative MRI and histologic features of explanted grafts were evaluated after 10 weeks.

Results

All pigs survived, with evidence of patent grafts on postoperative MRI. Graft inner diameter changes were 0.47 ± 2.31 mm in 3DTEVGs and -4.61 ± 2.15 mm in controls (P = .018). Mean main pulmonary artery wall shear stress was significantly lower in 3DTEVGs (7.12 ± 4.21 Pa) than in controls (18.15 ± 8.37 Pa; P = .0396). Histologic evaluation of 3DTEVGs showed a single layer of endothelial cells, an organized smooth muscle layer, and collagen deposition with a remaining scaffold area of 21.37% ± 20.46%.

Conclusions

Our patient-specific 3DTEVGs demonstrated optimal anatomic fit while maintaining ideal flow dynamics and promoting appropriate neovessel formation.

The role of venous pressure variability during hemodialysis in the prediction of impending arteriovenous graft occlusion

BACKGROUND

Elevated venous pressure during hemodialysis (VPHD) is associated with arteriovenous graft (AVG) stenosis. This study investigated the role of VPHD variations in the prediction of impending AVG occlusion.

METHODS

Data were retrieved from 118 operations to treat AVG occlusion (occlusion group) and 149 operations to treat significant AVG stenosis (stenosis group). In addition to analyzing the VPHD values for the three hemodialysis (HD) sessions prior to the intervention, VPHD values were normalized to mean blood pressure (MBP), blood flow rate (BFR), BFR × MBP, and BFR2 × MBP to yield ratios for analysis. The coefficient of variation (CV) was used to measure relative variations.

RESULTS

The within-group comparisons for both groups revealed no significant differences in the VPHD mean and CV values among the three HD sessions prior to intervention. However, the CVs for VPHD/MBP, VPHD/(BFR × MBP), and VPHD/(BFR2 × MBP) exhibited significant elevation in the occlusion group during the last HD session prior to intervention compared with both the penultimate and antepenultimate within-group HD data (p < 0.05). In the receiver operating characteristic curve analysis, the CV for VPHD/(BFR2 × MBP) was the only parameter able to discriminate between the last and the penultimate HD outcomes (p < 0.001). According to a multivariate analysis, after controlling for covariates, CV for VPHD/(BFR2 × MBP) >8.76% was associated with a higher risk of AVG thrombosis (odds ratio: 3.17, p < 0.001).

CONCLUSIONS

Increasing the variation in VPHD/(BFR2 × MBP) may increase the probability of AVG occlusion.

Evaluating Short-Term and Long-Term Risks Associated with Renal Artery Stenosis Position and Severity: A Hemodynamic Study

Background: Moderate renal artery stenosis (50-70%) may lead to uncontrolled hypertension and eventually cause irreversible damage to renal function. However, the clinical criteria for interventional treatment are still ambiguous in this condition. This study investigated the impact of the position and degree of renal artery stenosis on hemodynamics near the renal artery to assess the short-term and long-term risks associated with this disease. Methods: Calculation models with different degrees of stenosis (50%, 60%, and 70%) located at different positions in the right renal artery were established based on the computed tomography angiography (CTA) of a personalized case. And computational fluid dynamics (CFD) was used to analyze hemodynamic surroundings near the renal artery. Results: As the degree of stenosis increases and the stenosis position is far away from the aorta, there is a decrease in renal perfusion. An analysis of the wall shear stress (WSS)-related parameters indicated areas near the renal artery (downstream of the stenosis and the entrance of the right renal artery) with potential long-term risks of thrombosis and inflammation. Conclusion: The position and degree of stenosis play a significant role in judging short-term risks associated with renal perfusion. Moreover, clinicians should consider not only short-term risks but also independent long-term risk factors, such as certain regions of 50% stenosis with adequate renal perfusion may necessitate prompt intervention.

Passive performance evaluation and validation of a viscous impeller pump for subpulmonary fontan circulatory support

Patients with single ventricle defects undergoing the Fontan procedure eventually face Fontan failure. Long-term cavopulmonary assist devices using rotary pump technologies are currently being developed as a subpulmonary power source to prevent and treat Fontan failure. Low hydraulic resistance is a critical safety requirement in the event of pump failure (0 RPM) as a modest 2 mmHg cavopulmonary pressure drop can compromise patient hemodynamics. The goal of this study is therefore to assess the passive performance of a viscous impeller pump (VIP) we are developing for Fontan patients, and validate flow simulations against in-vitro data. Two different blade heights (1.09 mm vs 1.62 mm) and a blank housing model were tested using a mock circulatory loop (MCL) with cardiac output ranging from 3 to 11 L/min. Three-dimensional flow simulations were performed and compared against MCL data. In-silico and MCL results demonstrated a pressure drop of < 2 mmHg at a cardiac output of 7 L/min for both blade heights. There was good agreement between simulation and MCL results for pressure loss (mean difference - 0.23 mmHg 95% CI [0.24-0.71]). Compared to the blank housing model, low wall shear stress area and oscillatory shear index on the pump surface were low, and mean washout times were within 2 s. This study demonstrated the low resistance characteristic of current VIP designs in the failed condition that results in clinically acceptable minimal pressure loss without increased washout time as compared to a blank housing model under normal cardiac output in Fontan patients.