Physiological Flow Research Articles

Impact of compressed sensing (CS) acceleration of two-dimensional (2D) flow sequences in clinical paediatric cardiac magnetic resonance (CMR)

Abstract Background Two-dimensional (2D) through-plane phase-contrast (PC) cine flow imaging assesses shunts and valve regurgitations in paediatric CMR, and is considered the reference standard for Clinical quantification Of blood Flow (COF). However, the longer breath-hold (BH) for a flow cine can reduce patient compliance with possibly large respiratory maneuvers altering flow. Compressed sensing (CS) flow has not been widely evaluated in pediatric clinical CMR, although CS flow reduces scan time with persistent accuracy [1–3]. Kocaoglu et al applied CS to ascending and descending aorta and SVC with good results. We used main pulmonary artery (MPA) and sinotubular junction (STJ) planes as usual for clinical CMR. Purpose We hypothesise that reduced BH time by modest application of CS to 2D cine through-plane flows (Short BH quantification of Flow) (SBOF) retains accuracy while enabling faster and potentially more reliable paediatric flows. We therefore investigate the variance between conventional COF and new SBOF cine flows in paediatric CMR. Methods Paediatric patients were enrolled. Aortic (AO) and MPA COFs were planned from cines of the left and right ventricular outflow tracts. For AO flow the plane was placed at the STJ, and MPA flow was acquired above the pulmonary valve. The same planes were used for COF and SBOF flows at nominally similar parameters except the moderate application of CS exploiting redundancy across the cine frames, SBOF being segmented CS cines not real-time. CVI42 (5.10; Circle CVI) was used for flow analysis (single observer, 3 years' experience). Paired t-tests found the overall differences, and variability was defined at ±2SD for STJSV, MPASV, STJCO, MPACO, and Qp/Qs. Results and discussion 20 patients (mean age 13.7, range 10–17y) were enrolled (12 CHDs, 7 cardiomyopathies or other diseases). The BH times were COF mean 11.7s (range 8.4–20.9s) vs SBOF mean 6.5s (min 3.6–9.1s). For STJ flows the differences and variabilities between the COF and SBOF flows were SV 6.95±13.6 (ml/beat), CO 0.16±1.35 (l/min) and for MPA flows SV 2.95±12.3 (ml/beat), CO 0.27±0.96 (l/min) and for Qp/Qs were 0.04±0.19 by ml/beat and 0.02±0.23 by l/min. The mean differences were non significant, and variability between SBOF and COF was similar to intrasession repeatability of COF in a separate paediatric population at our centre (unpublished), that might arise from physiological flow changes, possibly in terms of pre and post load and heart rate. With shorter BHs also assisting patient compliance of the SBOF, physiological flow effects might be reduced, although given the variability in COV this was unconfirmed. Conclusion Moderate CS applied to clinical segmented-cine paediatric phase-contrast flows in the STJ and MPA planes did not degrade flow repeatability or cause bias. SBOF assists clinical flows by shorter BHs and also may aid compliance and reduce physiological variations. Funding Acknowledgement Type of funding sources: None.

Aortic flow patterns by 4D flow CMR in Marfan and Loeys-Dietz patients before and after valve sparing aortic root replacement: a comparison with healthy volunteers

Abstract Introduction Abnormal aortic flow patterns in patients with a connective tissue disorder (CTD), such as Marfan or Loeys-Dietz syndrome, may contribute to aortic root dilation [1,2]. Valve sparing aortic root replacement, which is effective in reducing the risk of aortic dissection in case of severe dilation, may also normalize flow patterns beyond the replaced aorta and potentially slow its progressive aortic dilation. Purpose To assess aortic flow dynamics in patients with a CTD by 4D flow cardiovascular magnetic resonance (CMR) before and after valve sparing aortic root replacement, and to compare the results with those of healthy volunteers (HV). Methods Patients with Marfan or Loeys-Dietz syndrome underwent two non-contrast enhanced 4D flow CMR, one before and another after undergoing valve sparing aortic root replacement. Healthy volunteers matched for age, sex and BSA were also included for comparison. Maximum velocity, in-plane rotational flow (IRF), systolic flow reversal ratio (SFRR) and wall shear stress (WSS) magnitude and its axial and circumferential components were obtained at 24 planes covering the thoracic aorta from the sinotubular junction to the descending aorta at the diaphragmatic level [3–5]. Results Sixteen patients and 21 healthy volunteers were included. Demographic and clinical data is presented in Table. The mean time between the CMR prior and posterior to surgery was 15 months. Compared to HV, patients with CTD before intervention presented lower maximum velocity at the proximal ascending aorta (Fig. 1A), lower IRF and circumferential WSS at the arch and the proximal descending aorta (Fig. 1B and F), lower magnitude and axial WSS at the proximal ascending and descending aorta (Fig. 1E and D), and increased SFRR at the proximal descending aorta (Fig. 1C). The intervention completely restored maximum velocity and partially-restored physiological helical flow and circumferential WSS, but barely improved axial WSS and SFRR. Conclusion Valve sparing aortic root replacement in patients with Marfan or Loeys-Dietz syndrome partially restore to physiological level both in-plane rotational flow and circumferential wall shear stress in the descending aorta. This flow normalization may contribute to prevent progressive dilation after the surgery. Funding Acknowledgement Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Instituto de Salud Carlos III (Spain) (PI17/00381)Spanish Society of Cardiology (SEC/FEC-INV-CLI 20/015)

Primary human monocytes are stimulated in a pro-atherosclerotic manner in hyperhomocysteine conditions by attenuated PTEN phosphatase function

Abstract Purpose Monocytes are essential for atherosclerosis and hereby crucial for the detrimental consequences of cardiovascular diseases like coronary heart disease. Interestingly, homocysteine (HCY) was identified as an idependent risk factor for atherosclerosis development. However, the specific implication of HCY on monocytes has not yet been clarified and was therefore investigated in the present study. Methods Primary human monocytes, isolated from peripheral blood through the immuno-magnetic method, were treated with a clinically relevant dose of 400 μM HCY for 24 hours. Monocyte migration was investigated with transwell migration assays. Adhesion to inflamed endothelium (HUVECs) was studied under static and physiological flow conditions. Expression of relevant molecules was quantified with Western Blot, RT-qPCR and FACS. 5-azacytidine (AZA) was used to inhibit DNA methyltransferase 1 (DNMT1) and SF1670 to inhibit PTEN. Results First, we studied monocyte migration phenotype. Under hyperhomocysteine conditons monocytes revealed elevated chemokinesis and enhance chemotaxis towards MCP-1. In addition, monocytes show a pro-adhesive phenotype under HCY treatment which was indicated by heightened adhesion to inflamed endothelial cells, both in static and physiological flow conditions. These data could be sustained by observation of HCY-induced augmented expression of adhesion molecule CD11a on primary human monocytes. Interestingly, we observed decreased PTEN phosphatase function and activity in HCY-treated monocytes, which was reflected downstream in increased activation of AKT at serine 473. Based on these data, it was also possible to induce the pro-migratory phenotype in monocytes by pharmacological inhibition of PTEN alone. Since HCY can modify the methylation status of PTEN and hereby regulates its expression, we inhibited DNMT1 with AZA which could prevent downregulation of PTEN expression by HCY treatment. In addition, through inhibition of DNMT1 HCY-induced aberrant migration and adhesion was rescued. In line with that, HCY-induced pro-migratory and pro-adhesive phenotype was also rescued by co-treatment with the cofactors (30 μM Vitamin B12 and 3 μM folic acid) responsible for homocysteine to methionine catabolism due to normalized PTEN expression. Conclusions The present work deciphers a previously unknown mechanism how an increased concentration of HCY induces a pro-atherosclerotic activation of monocytes. Accumulation of HCY leads to a methylation-dependent inactivation of PTEN phosphatase. This subsequently causes increased phosphorylation of AKT at serine 473, which results in an augmented migration behaviour of monocytes. At the same time, we were able to reduce HCY-induced aberrant monocyte activation by inhibiting DNTM1 or by interfering with HCY metabolism by adding vitamin B12 or folic acid. In summary, these findings provide a new approach to reset pro-atherosclerotic monocytes in hyperhomocysteinemic conditions. Funding Acknowledgement Type of funding sources: Other. Main funding source(s): IZKF SEED Project 14/20

Flow Behaviour and Wall Shear Stress Derivatives in Abdominal Aortic Aneurysm Models: A Detailed CFD Analysis into Asymmetry Effect

Assessing the risk of rupture is extremely important to reduce the mortality of the abdominal aortic aneurysm (AAA). Current clinical guidelines suggest considering the maximum diameter as a criterion for planning and surgical intervention; however, this approach is too simplistic and overlooks other morphological parameters that are associated with the risk of rupture. The aim of this paper is to study the thrombogenicity and to predict the risk of AAA rupture by taking into consideration the geometrical asymmetry of the aneurysm, studying its effect on blood flow behaviour and vortical structure, spatiotemporal distribution of wall shear stresses (WSS), and their related parameters. To show the effect of asymmetry on blood flow dynamics and hemodynamic forces, five virtual models were constructed using five values of geometrical asymmetry ratio β ranging from β=0.2 (asymmetric model; AM) to β=1 (symmetric model; SM). Simulations were run for each geometry under transient physiological flow conditions using finite volume discretization. Resting flow rate was investigated in these models and our results demonstrate that the asymmetry of the aneurysm has a clear effect on the flow behaviour, and consequently on WSS distribution, oscillatory shear index (OSI) and time averaged wall shear stress (TAWSS). Furthermore, these preliminary findings suggest that thrombus formation and rupture risk are more probable in an asymmetric abdominal aortic aneurysm.

Physiologic Flow Diversion Coiling Technique for Wide-Necked Aneurysms with an Asymmetric Bidirectional Flow at the Aneurysm Neck.

Wide-necked aneurysms in the circle of Willis (CoW) are prone to recur due to reciprocal bidirectional flow. We present a novel concept of coil embolization to prevent recurrence that uses physiologic flow diversion at the CoW. We enrolled 14 patients (15 aneurysms) who underwent aneurysm coiling for wide-necked aneurysms with asymmetric bidirectional inflow into the aneurysm. Four patients had recurrent aneurysms after coiling. The concept of physiologic flow diversion included obliterating antegrade flow into the aneurysm sac as well as opposite CoW flow by performing compact coil packing with intentional protrusion out of the aneurysm neck to the communicating part. Fifteen aneurysms, including 4 recurrent aneurysms, in an anterior communicating artery (n=7), posterior communicating artery (n=5), and tip of the basilar artery (n=3) were treated with coil embolization (n=10) and stent-assisted coiling (n=5). All aneurysms had a wide neck, and the mean largest diameter was 9.0 mm. The mean packing density was 45.1%. Twelve aneurysms were completely occluded, and 3 aneurysms had tiny residual neck remnants. There was neither a neurological event nor recurrence during the mean 12.5 months of follow-up. Wide-necked aneurysms at the CoW tend to recur. As a strategy to prevent a recurrence, physiologic flow diversion can be an option in treating wide-necked aneurysms in the CoW.

Atheroprone fluid shear stress-regulated ALK1-Endoglin-SMAD signaling originates from early endosomes

BackgroundFluid shear stress enhances endothelial SMAD1/5 signaling via the BMP9-bound ALK1 receptor complex supported by the co-receptor Endoglin. While moderate SMAD1/5 activation is required to maintain endothelial quiescence, excessive SMAD1/5 signaling promotes endothelial dysfunction. Increased BMP signaling participates in endothelial-to-mesenchymal transition and inflammation culminating in vascular diseases such as atherosclerosis. While the function of Endoglin has so far been described under picomolar concentrations of BMP9 and short-term shear application, we investigated Endoglin under physiological BMP9 and long-term pathophysiological shear conditions.ResultsWe report here that knock-down of Endoglin leads to exacerbated SMAD1/5 phosphorylation and atheroprone gene expression profile in HUVECs sheared for 24 h. Making use of the ligand-trap ALK1-Fc, we furthermore show that this increase is dependent on BMP9/10. Mechanistically, we reveal that long-term exposure of ECs to low laminar shear stress leads to enhanced Endoglin expression and endocytosis of Endoglin in Caveolin-1-positive early endosomes. In these endosomes, we could localize the ALK1-Endoglin complex, labeled BMP9 as well as SMAD1, highlighting Caveolin-1 vesicles as a SMAD signaling compartment in cells exposed to low atheroprone laminar shear stress.ConclusionsWe identified Endoglin to be essential in preventing excessive activation of SMAD1/5 under physiological flow conditions and Caveolin-1-positive early endosomes as a new flow-regulated signaling compartment for BMP9-ALK1-Endoglin signaling axis in atheroprone flow conditions.

Effect of Temperature Dependent Sink on Peristaltic Transport in a Differentially Heated Vertical Annulus Filled with a Porous Material

In this article, we have presented a mathematical analysis to study the peristaltic flow through vertical annulus filled with a porous material bounded by two concentric uniform tubes. This analysis can serve as a model which may help in understanding the mechanism of physiological flows and heat transfer in a vertical annulus subject to differentially heating in the presence of a temperature dependent sink. The inner tube is uniform and rigid, while the outer tube has a sinusoidal wave traveling down its wall. It is analyzed in a wave frame of reference moving with velocity of the wave under a zero Reynolds number and long wavelength approximation in the presence of a temperature dependent sink. The analytical solutions are obtained for temperature, axial velocity, stream function and axial pressure-gradient. We also present numerical integration in order to analyze the pressure rise and frictional forces on the inner and outer tubes. In order to have an estimate of the quantitative effects of various emerging physical parameters on flow characteristics which are involved in the solutions of the considered analysis, we have used the MATLAB software for plotting the contour graphs and discussed in details. We have observed that the intensity of heat sink increases when amplitude ratio is increased. The trapped bolus appears when Darcy number is small but the important observation is that for the large values of Darcy number, the trapped bolus disappears and fluid moves like a block, which shows some sort of rigidity.

Noncontrast time-resolved pulmonary magnetic resonance angiography with consecutive beam saturation pulse and variable flip angles using three-dimensional fast spin echo: A preliminary study

To develop and validate a novel noncontrast time-resolved magnetic resonance angiography (NC TR-MRA) using consecutive beam pulses with variable flip angles for visualizing hemodynamics in the pulmonary artery, we performed phantom and volunteer studies and applied the novel NC TR-MRA to a 51-year-old woman with pulmonary arteriovenous malformation (PAVM).The novel NC TR-MRA sequence utilized consecutive multiple-beam saturation pulses with variable flip angles considering venous blood T1 relaxation to alter the visualized blood signal length. The flowing blood signal length is suppressed according to the number of beam saturation pulses. NC TR-MRA in each flow phase was assessed by subtracting the images with and without beam saturation pulses. In the flow phantom study, three flow velocities were used to simulate physiological pulmonary arterial blood flow. Signal profiles along the flow direction were evaluated in each flow phase. In the volunteer study, five healthy volunteers were recruited, and NC TR-MRA was applied to evaluate relationships between the flow-saturated time and signal enhancement rates. Four regions of interest (ROIs) were determined on the proximal and distal portions of the right basal artery. A patient with PAVM was included to validate whether a PAVM lesion could be visualized using NC TR-MRA. The visualized flow signal lengths extended proportionally with the number of beam saturation pulses in the steady-flow phantom at all velocities. In the volunteer study, NC TR-MRA images showed signal enhancement from the proximal to distal portions of the right basal artery with increase in the flow-saturated time. Signal enhancement rates in all ROIs were significantly positively correlated with the flow-saturated time (p < 0.001 in all ROIs). Further, the lesion and its hemodynamics could be explicitly visualized in the patient with PAVM. Hence, NC TR-MRA using beam saturation pulse can visualize the hemodynamics of the pulmonary artery and may be useful for diagnosing and following patients with PAVM.

A Live Cell Imaging Microfluidic Model for Studying Extravasation of Bloodborne Bacterial Pathogens

Bacteria that migrate (extravasate) out of the bloodstream during vascular dissemination can cause secondary infections in many tissues and organs, including the brain, heart, liver, joints, and bone with clinically serious and sometimes fatal outcomes. The mechanisms by which bacteria extravasate through endothelial barriers in the face of blood flow-induced shear stress are poorly understood, in part because individual bacteria are rarely observed traversing endothelia in vivo, and in vitro model systems inadequately mimic the vascular environment. To enable the study of bacterial extravasation mechanisms, we developed a transmembrane microfluidics device mimicking human blood vessels. Fast, quantitative, three-dimensional live cell imaging in this system permitted single-cell resolution measurement of the Lyme disease bacterium Borrelia burgdorferi transmigrating through monolayers of primary human endothelial cells under physiological shear stress. This cost-effective, flexible method was 10,000 times more sensitive than conventional plate reader-based methods for measuring transendothelial migration. Validation studies confirmed that B. burgdorferi transmigrate actively and strikingly do so at similar rates under static and physiological flow conditions. This method has significant potential for future studies of B. burgdorferi extravasation mechanisms, as well as the transendothelial migration mechanisms of other disseminating bloodborne pathogens.

Polymeric nanoparticles targeting Sialyl-Tn in gastric cancer: A live tracking under flow conditions.

Drug delivery using nanoparticles (NPs) represents a potential approach for therapy in cancer, such gastric cancer (GC) due to their targeting ability and controlled release properties. The use of advanced nanosystems that deliver anti-cancer drugs specifically to tumor cells may strongly rely on the expression of cancer-associated targets. Glycans aberrantly expressed by cancer cells are attractive targets for such delivery strategy. Sialylated glycans, such as Sialyl-Tn (STn) are aberrantly expressed in several epithelial tumors, including GC, being a potential target for a delivery nanosystem. The aim of this study was the development of NPs surface-functionalized with a specific antibody targeting the STn glycan and further evaluate this nanosystem effectiveness regarding its specificity and recognition capacity. Our results showed that the NPs surface-functionalized with anti-STn antibody efficiently are recognized by cells displaying the cancer-associated STn antigen under static and live cell monitoring flow conditions. This uncovers the potential use of such NPs for drug delivery in cancer. However, flow exposure was disclosed as an important biomechanical parameter to be taken into consideration. Here we presented an innovative and successful methodology to live track the NPs targeting STn antigen under shear stress, simulating the physiological flow. We demonstrate that unspecific binding of NPs agglomerates did not occur under flow conditions, in contrast with static assays. This robust approach can be applied for in vitro drug studies, giving valuable insights for in vivo studies.

Conformation of von Willebrand factor in shear flow revealed with stroboscopic single-molecule imaging

Abstractvon Willebrand factor (VWF) is a multimeric blood protein that acts as a mechanical probe, responding to changes in flow to initiate platelet plug formation. Previously, our laboratory tests had shown that using single-molecule imaging that shear stress can extend surface-tethered VWF, but paradoxically, we found that the required shear stress was higher than reported for free-in-flow VWF, an observation inconsistent with basic physical principles. To resolve this inconsistency critical to VWF’s molecular mechanism, we measured free-VWF extension in shear flow using pulsed laser stroboscopic imaging of single molecules. Here, laser pulses of different durations are used to capture multiple images of the same molecule within each frame, enabling accurate length measurements in the presence of motion blur. At high shear stresses, we observed a mean shift in VWF extension of <200 nm, much shorter than the multiple-micron extensions previously reported with no evidence for the predicted sharp globule-stretch conformational transition. Modeling VWF with a Brownian dynamics simulation, our results were consistent with VWF behaving as an uncollapsed polymer rather than the theorized compact ball. The muted response of free VWF to high shear rates implies that the tension experienced by free VWF in physiological shear flow is lower than indicated by previous reports and that tethering to platelets or the vessel wall is required to mechanically activate VWF adhesive function for primary hemostasis.

EP47.03: Physiological microvascular blood flow profile of the endometrium during the menstrual cycle described using superb‐microvascular imaging

EP47.03: Physiological microvascular blood flow profile of the endometrium during the menstrual cycle described using superb‐microvascular imaging

Evolution of vortex structures in an open deep cavity under pulsatile flow conditions: An experimental study

Experiments have been conducted to investigate the vortex dynamics in a deep open cavity driven by pulsatile flows. Physiological flow waveforms have been examined for mean Re ranging from 200 to 1000 and Wo of 10.2, 12.4, and 17.6, with Strouhal numbers (Str, as a function of Re and Wo) ranging from 0.065 to 0.98. Results show that a two-primary-vortex system develops, similar to a steady driven cavity flow, but it exhibits more dynamic behaviors as it evolves during a cycle. Five stages of vortex evolution are defined: generation, traveling, merging, stretching, and weakening. As Re increases, the first three stages occur faster and earlier in a cycle, allowing more time for the top primary vortex to interact with the rear wall and for the bottom vortex to develop. The opposite trend is found as Wo increases. While the flow strength increases with Re, the vortex patterns are more correlated with Str, which is proportional to the Wo square and inversely proportional to Re: vortices are symmetric at low Str, but become more distorted at high Str. A critical Str exists beyond which the bottom vortex would not develop inside the cavity. Results also suggest that an increasing Wo causes a more significant increase in the in-cavity vortex strength and flow unsteadiness compared to an increasing Re. The peak flow unsteadiness inside the cavity occurs at a later phase compared with that of the main flow. The normalized mass flux ratio and the normalized cavity kinetic energy are both linearly proportional to the Strouhal number.

Biphasic flow dynamics and polarized mass transportation in branched hepatic sinusoids.

In fatty liver diseases, such as liver fibrosis and liver cirrhosis, blood flow in hepatic sinusoids, an elementary building block of the liver lobule, tends to bypass through collateral vessels inside sinusoids and presents distinct sinusoidal flows compared to normal physiological flows. It remains unclear in those flow characteristics in branched sinusoids and the correlation of pathological flows with liver lesions, mainly due to the difficulty of direct hemodynamics measurements in the sinusoids. Here, we developed a dual-branched theoretical model of hepatic sinusoidal flow to elucidate the relevant flow dynamics and mass transport. Numerical simulations, based on the lattice Boltzmann method, indicated that the flow velocity distribution in hepatic sinusoids is mainly dominated by endothelium permeability and presents a non-monotonic variation with the permeability at the fusion segment of these branched sinusoids. Flow-induced shear stress on the endothelium at the side of the Disse space exhibited a biphasic pattern, yielding a low shear stress region at the junctional site. Meanwhile, a highly polarized distribution of lipoproteins concentration was also presented at the low shear stress region, indicating a localized accumulation of typical hepatic serum proteins. Thus, this work provides the basic understanding of blood flow features and mass transport regulations in branched hepatic sinusoids.

Development of physiologically-based toxicokinetic-toxicodynamic (PBTK-TD) model for 4-nonylphenol (4-NP) reflecting physiological changes according to age in males: Application as a new risk assessment tool with a focus on toxicodynamics

Environmental exposure to 4-nonylphenol (4-NP) is extensive, and studies related to human risk assessment must continue. Especially, prediction of toxicodynamics (TDs) related to reproductive toxicity in males is very important in risk-level assessment and management of 4-NP. This study aimed to develop a physiologically-based-toxicokinetic-toxicodynamic (PBTK-TD) model that added a TD prostate model to the previously reported 4-n-nonylphenol (4-n-NP) physiologically-based-pharmacokinetic (PBPK) model. Modeling was performed under the assumption of similar TKs between 4-n-NP and 4-NP because TK experiments on 4-NP, a random-mixture, are practically difficult. This study was very important to quantitatively predict the TKs and TDs of 4-NP by age at exposure using an advanced PBTK-TD model that reflected physiological-changes according to age. TD-modeling was performed based on the reported toxic effects of 4-NP on RWPE-1 cells, a human-prostate-epithelial-cell-line. Through a meta-analysis of reported human physiological data, body weight, tissue volume, and blood flow rate patterns according to age were mathematically modeled. These relationships were reflected in the PBTK-TD model for 4-NP so that the 4-NP TK and TD changes according to age and their differences could be confirmed. Differences in TK and TD parameters of 4-NP at various ages were not large, within 3.61-fold. Point-of-departure (POD) and reference-doses for each age estimated using the model varied as 426.37–795.24 and 42.64–79.52 μg/kg/day, but the differences (in POD or reference doses between ages) were not large, at less than 1.87-times. The PBTK-TD model simulation predicted that even a 100-fold 4-NP PODman dose would not have large toxicity to the prostate. With a focus on TDs, the predicted maximum possible exposure of 4-NP was as high as 6.06–23.60 mg/kg/day. Several toxicity-related values estimated by the dose-response curve were higher than those calculated, depending upon the PK or TK, which would be useful as a new exposure limit for prostate toxicity of 4-NP.

A pulmonary endothelial amplification loop aggravates ex-vivo transfusion-related acute lung injury via increased toll-like receptor 4 and intra-cellular adhesion molecule-1 expression.

Transfusion-Related Acute Lung Injury (TRALI) is a life-threatening complication of blood transfusions characterized by pulmonary endothelial cell damage and edema, with a high incidence in critically ill patients. The pathophysiology of TRALI is unresolved, but can generally be hypothesized to follow a 2-hit model in which the first hit is elicited by the underlying clinical condition of the patient (e.g., inflammation, which can be reflected by LPS in experimental models), and the second hit is delivered by the blood transfusion product (e.g., HLA class I antibodies). Here, we report a synergistic role for LPS and HLA class I antibody binding to pulmonary endothelium resulting in enhanced inflammatory responses. Pulmonary endothelial cells were treated with PBS or low-dose LPS, exclusively or in combination with anti-HLA class I. Endothelial surface expression of HLA class I, TLR4, and inflammatory marker ICAM-1 were measured, and trans-endothelial migration (TEM) of neutrophils was investigated. LPS treatment of pulmonary endothelium enhanced HLA class I antibody binding, and combined LPS and HLA class I antibody binding enhanced TLR4 (LPS receptor) and ICAM-1 expression on the endothelial cell surface. Low-dose LPS and HLA antibody together also increased neutrophil TEM under physiological flow by on average 5-fold. We conclude that LPS and anti-HLA class I antibody have the ability to activate the pulmonary endothelium into a spiral of increasing inflammation, opening the opportunity to potentially block TLR4 to prevent or reduce the severity of TRALI in vivo.

The Modular µSiM Reconfigured: Integration of Microfluidic Capabilities to Study In Vitro Barrier Tissue Models under Flow.

Microfluidic tissue barrier models have emerged to address the lack of physiological fluid flow in conventional "open-well" Transwell-like devices. However, microfluidic techniques have not achieved widespread usage in bioscience laboratories because they are not fully compatible with traditional experimental protocols. To advance barrier tissue research, there is a need for a platform that combines the key advantages of both conventional open-well and microfluidic systems. Here, a plug-and-play flow module is developed to introduce on-demand microfluidic flow capabilities to an open-well device that features a nanoporous membrane and live-cell imaging capabilities. The magnetic latching assembly of this design enables bi-directional reconfiguration and allows users to conduct an experiment in an open-well format with established protocols and then add or remove microfluidic capabilities as desired. This work also provides an experimentally-validated flow model to select flow conditions based on the experimental needs. As a proof-of-concept, flow-induced alignment of endothelial cells and the expression of shear-sensitive gene targets are demonstrated, and the different phases of neutrophil transmigration across a chemically stimulated endothelial monolayer under flow conditions are visualized. With these experimental capabilities, it is anticipated that both engineering and bioscience laboratories will adopt this reconfigurable design due to the compatibility with standard open-well protocols.

Pulmonary Venous Gradients in Healthy Controls and Following the Repair of Total Anomalous Pulmonary Venous Return.

The percent of children who can achieve a normal and physiologic pulmonary venous gradient and flow following the repair of Total Anomalous Pulmonary Venous Return (TAPVR) is not known. Pulmonary venous confluence gradients from infants with supra-, infra-, or mixed TAPVR, repaired using a direct anastomotic connection were measured. Data from age, weight, and gender-matched controls established the normal pulmonary venous gradient range (0.30-0.94mmHg). TAPVR subjects were divided into three groups: (I) pulmonary venous gradient < 2×normal with multiphasic flow (II) pulmonary venous gradient > 2×normal with multiphasic flow, and (III) pulmonary venous gradient > 2×normal with monophasic flow. From 63 children following TAPVR repair and 63 matched controls, pulmonary venous gradients were significantly lower [0.5mmHg (IQR:0.4, 0.6) vs 1.6mmHg (IQR:1.0, 2.4); p < 0.001], and multiphasic flow more frequent (100 vs. 84.1%; p = 0.001) within the control group. There were 38 children (60.3%) in group I, 15 (23.8%) in group II, and 10 (15.8%) in group III. Children in Group I were significantly older at the time of repair, had shorter cardiopulmonary bypass times, and did not utilize deep hypothermic circulatory arrest (DHCA). Multivariate analysis confirmed that avoiding DHCA [Odds Ratio 0.931 (0.913,0.994; p = 0.002)] and shorter cardiopulmonary bypass times [Odds Ratio 0.962 (0.861,0.968; p = 0.02)] during repair were associated with the lowest pulmonary venous gradients and multiphasic flow. Following TAPVR repair with a direct anastomosis, the majority of children can achieve a gradient two times normal or less with multiphasic pulmonary venous flow.

Hemodynamic and anatomic changes after fetal aortic valvuloplasty are associated with procedural success and postnatal biventricular circulation.

There are minimal data characterizing the trajectory of left heart growth and hemodynamics following fetal aortic valvuloplasty (FAV). This retrospective study included patients who underwent FAV between 2000 and 2019, with echocardiograms performed pre-FAV, immediately post-FAV, and in late gestation. Of 118 fetuses undergoing FAV, 106 (90%) underwent technically successful FAV, of which 55 (52%) had biventricular circulation. Technically successful FAV was associated with improved aortic valve growth (p<0.001), sustained antegrade aortic arch (AoA) flow (p=0.02), improved mitral valve (MV) inflow pattern (p=0.002), and favorable patent foramen ovale (PFO) flow pattern (p=0.004) from pre-FAV to late gestation. Compared to patients with univentricular outcome, patients with biventricular outcome had less decrement in size of the left ventricle (LV) (p<0.001) and aortic valve (p=0.005), as well as more physiologic PFO flow (p<0.001) and antegrade AoA flow (p<0.001) from pre-FAV to late gestation. In multivariable analysis, echocardiographic predictors of biventricular outcome were less decline in LV end diastolic dimension (p<0.001), improved PFO flow (p=0.004), and sustained antegrade AoA flow (p=0.002) from pre-FAV to late gestation. Stabilization of left heart growth and improved hemodynamics following successful FAV through late gestation are associated with postnatal biventricular circulation.

Endothelial Responses to Curvature-Induced Flow Patterns in Engineered Cerebral Aneurysms.

Hemodynamic factors have long been associated with clinical outcomes in the treatment of cerebral aneurysms. Computational studies of cerebral aneurysm hemodynamics have provided valuable estimates of the mechanical environment experienced by the endothelium in both the parent vessel and aneurysmal dome walls and have correlated them with disease state. These computational-clinical studies have recently been correlated with the response of endothelial cells (EC) using either idealized or patient-specific models. Here, we present a robust workflow for generating anatomic-scale aneurysm models, establishing luminal cultures of ECs at physiological relevant flow profiles, and comparing EC responses to curvature mediated flow. We show that flow patterns induced by parent vessel curvature produce changes in wall shear stress (WSS) and wall shear stress gradients (WSSG) that are correlated with differences in cell morphology and cellular protein localization. Cells in higher WSS regions align better with the flow and display strong Notch1-extracellular domain (ECD) polarization, while, under low WSS, differences in WSSG due to curvature change were associated with less alignment and attenuation of Notch1-ECD polarization in ECs of the corresponding regions. These proof-of-concept results highlight the use of engineered cellularized aneurysm models for connecting computational fluid dynamics to the underlying endothelial biology that mediates disease.