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Mechanical ventilation and extracorporeal membrane oxygenation are the only immediate options available for patients with respiratory failure. However, these options present significant shortcomings. To address this unmet need for respiratory support, innovative respiratory assist devices are being developed. In this study, we present the computational model-based design, and analysis of functional characteristics and hemocompatibility performance, of an innovative wearable artificial pump-lung (APL) for ambulatory respiratory support. Computer-aided design and computational fluid dynamics (CFD)-based modeling were utilized to generate the geometrical model and to acquire the fluid flow field, gas transfer, and blood damage potential. With the knowledge of flow field, gas transfer, and blood damage potential through the whole device, design parameters were adjusted to achieve the desired specifications based on the concept of virtual prototyping using the computational modeling in conjunction with consideration of the constraints on fabrication processes and materials. Based on the results of the CFD design and analysis, the physical model of the wearable APL was fabricated. Computationally predicted hydrodynamic pumping function, gas transfer, and blood damage potential were compared with experimental data from in vitro evaluation of the wearable APL. The hydrodynamic performance, oxygen transfer, and blood damage potential predicted with computational modeling, along with the in vitro experimental data, indicated that this APL meets the design specifications for respiratory support with excellent biocompatibility at the targeted operating condition. [ABSTRACT FROM AUTHOR]

In this article, the authors discuss various articles in this issue of the periodical on design and development of blood-contacting medical devices.

Background: Neutrophils take part in the innate immune response, phagocytosis, and pro‐inflammatory cytokine release. The phagocytic capacity of circulating neutrophils in patients on continuous flow (CF) ventricular assist device (VAD) has not been well studied. Methods: Blood samples from 14 patients undergoing CF‐VAD implantation were collected and analyzed preoperatively (at baseline) and on postoperative days (POD) 3, 7, 14, and 28. Flow cytometry was used to assess the surface expression levels of CD62L, CD162, and macrophage antigen‐1 (MAC‐1) and neutrophil phagocytic capacity. Interleukin 1 (IL1), IL6, IL8, TNF‐α, neutrophil elastase, and myeloperoxidase in plasma were measured using enzyme‐linked immunosorbent assays. Results: Among the 14 patients, seven patients had preoperative bridge device support. Relative to baseline, patients with no bridge device had elevated leukocyte count and neutrophil elastase by POD3 which normalized by POD7. Neutrophil activation level, IL6, IL8, and TNF‐α increased by POD3 and sustained elevated levels for 7–14 days postoperatively. Elevated neutrophil phagocytic capacity persisted even until POD28. Similar patterns were observed in patients on a preoperative bridge device. Conclusions: Neutrophil activation and phagocytic capacity increased in response to VAD support, while inflammatory cytokines remain elevated for up to 2 weeks postoperatively. These findings may indicate that VAD implantation elicits circulating neutrophils to an abnormal preemptive phagocytotic phenotype. [ABSTRACT FROM AUTHOR]

Background Methods Results Conclusions High mechanical shear stress (HMSS) generated by blood pumps during mechanical circulatory support induces blood damage (or function alteration) not only of blood cell components but also of plasma proteins.In the present study, fresh, healthy human blood was used to prime a blood circuit assisted by a CentriMag centrifugal pump at a flow rate of 4.5 L/min under three pump pressure heads (75, 150, and 350 mm Hg) for 4 h. Blood samples were collected for analyses of plasma‐free hemoglobin (PFH), von Willebrand factor (VWF) degradation and platelet glycoprotein (GP) IIb/IIIa receptor shedding.The extent of all investigated aspects of blood damage increased with increasing cross‐pump pressure and duration. Loss of high‐molecular‐weight multimers (HMWM)‐VWF in Loop 2 and Loop 3 significantly increased after 2 h. PFH, loss of HMWM‐VWF, and platelet GPIIb/IIIa receptor shedding showed a good linear correlation with mean shear stress corresponding to the three pump pressure heads.HMSS could damage red blood cells, cause pathological VWF degradation, and induce platelet activation and platelet receptor shedding. Different blood components can be damaged to different degrees by HMSS; VWF and VWF‐enhanced platelet activation may be more susceptible to HMSS. [ABSTRACT FROM AUTHOR]

Background: von Willebrand factor (vWF) plays a crucial role in physiological hemostasis through platelet and subendothelial collagen adhesion. However, its role in shear‐induced platelet activation and functional alteration under non‐physiological conditions common to blood‐contacting medical devices (BCMDs) is not well investigated. Methods: Fresh healthy human blood was treated with an anti‐vWF antibody to block vWF–GPIbα interaction. Untreated blood was used as a control. They were exposed to three levels of non‐physiological shear stress (NPSS) (75, 125, and 175 Pa) through a shearing device with an exposure time of 0.5 s to mimic typical shear conditions in BCMDs. Flow cytometric assays were used to measure the expression levels of PAC‐1 and P‐Selectin and platelet aggregates for platelet activation and the expression levels of GPIbα, GPIIb/IIIa, and GPVI for receptor shedding. Collagen/ristocetin‐induced platelet aggregation capacity was characterized by aggregometry. Results: The levels of platelet activation and aggregates increased with increasing NPSS in the untreated blood. More receptors were lost with increasing NPSS, resulting in a decreased capacity of collagen/ristocetin‐induced platelet aggregation. In contrast, the increase in platelet activation and aggregates after exposure to NPSS, even at the highest level of NPSS, was significantly lower in treated blood. Nevertheless, there was no notable difference in receptor shedding, especially for GPIIb/IIIa and GPVI, between the two blood groups at the same level of NPSS. The block of vWF exacerbated the decreased capacity of collagen/ristocetin‐induced platelet aggregation. Conclusions: High NPSS activates platelets mainly by enhancing the vWF–GPIbα interaction. Platelet activation and receptor shedding induced by high NPSS likely occur through different pathways. [ABSTRACT FROM AUTHOR]

Background: Although extracorporeal membrane oxygenation (ECMO) has been used to provide temporary support for pediatric patients suffering severe respiratory or cardiac failure since 1970, ECMO systems specifically designed for pediatric patients, particularly for long‐term use, remain an unmet clinical need. We sought to develop a new pediatric ECMO system, that is, pediatric pump‐lung (PPL), consisting of a unique cylinder oxygenator with an outside‐in radial flow path and a centrifugal pump. Methods: Computational fluid dynamics was used to analyze the blood fluid field for optimized biocompatible and gas exchange performances in terms of flow characteristics, hemolysis, and gas transfer efficiency. Ovine blood was used for in vitro hemolysis and gas transfer testing. Results: Both the computational and experimental data showed that the pressure drop through the PPL's oxygenator is significantly low, even at a flow rate of more than 3.5 L/min. The PPL showed better hemolysis performance than a commercial ECMO circuit consisting of the Quadrox‐iD pediatric oxygenator and the Rotaflow pump at a 3.5 L/min flow rate and 250 mm Hg afterload pressure. The oxygen transfer rate of the PPL can reach over 200 mL/min at a flow rate of 3.5 L/min. Conclusions: The PPL has the potential to provide adequate blood pumping and excellent respiratory support with minimal risk of hemolysis for a wide range of pediatric patients. [ABSTRACT FROM AUTHOR]

Thrombosis and bleeding are devastating adverse events in patients supported with blood-contacting medical devices (BCMDs). In this study, we delineated that high non-physiological shear stress (NPSS) caused platelet dysfunction that may contribute to both thrombosis and bleeding. Human blood was subjected to NPSS with short exposure time. Levels of platelet surface GPIbα and GPVI receptors as well as activation level of GPIIb/IIIa in NPSS-sheared blood were examined with flow cytometry. Adhesion of sheared platelets on fibrinogen, von Willibrand factor (VWF), and collagen was quantified with fluorescent microscopy. Ristocetin- and collagen-induced platelet aggregation was characterized by aggregometry. NPSS activated platelets in a shear and exposure time-dependent manner. The number of activated platelets increased with increasing levels of NPSS and exposure time, which corresponded well with increased adhesion of sheared platelets on fibrinogen. Concurrently, NPSS caused shedding of GPIbα and GPVI in a manner dependent on shear and exposure time. The loss of intact GPIbα and GPVI increased with increasing levels of NPSS and exposure time. The number of platelets adhered on VWF and collagen decreased with increasing levels of NPSS and exposure time, respectively. The decrease in the number of platelets adhered on VWF and collagen corresponded well with the loss in GPIbα and GPVI on platelet surface. Both ristocetin- and collagen-induced platelet aggregation in sheared blood decreased with increasing levels of NPSS and exposure time. The study clearly demonstrated that high NPSS causes simultaneous platelet activation and receptor shedding, resulting in a paradoxical effect on platelet function via two distinct mechanisms. The results from the study suggested that the NPSS could induce the concurrent propensity for both thrombosis and bleeding in patients. [ABSTRACT FROM AUTHOR]

Non-physiological shear stress (NPSS) and thrombin have two distinct mechanisms for activating platelets. NPSS in mechanically assisted circulation (MAC) devices can cause platelet dysfunction, e.g., by shedding its key receptors. In addition, patients with heart failure have increased levels of thrombin generation, which may further affect the NPSS-induced platelet dysfunction, resulting in device-associated complications. This study aimed to assess the combined effect of NPSS and thrombin in platelet activation, expression of adhesion receptors on the platelet surface, and alterations of platelet aggregation. Fresh human blood from healthy donors was divided into two groups; one group was treated by adding 0.01 U/mL thrombin, and another group not treated with thrombin served as a control comparison. They were then pumped through a novel blood shearing device which produces similar shear stress conditions to those in the MAC devices. Three levels of NPSS (i.e., 75, 125, and 175 Pa) with a 1.0 s exposure time were selected for the shearing conditions. Expression of platelet activation markers (PAC-1, activated GPIIb/IIIa and CD62P, platelet surface P-selectin) were investigated along with the shedding of platelet receptors (GPIb, GPIIb/IIIa, and GPVI), generation of platelet microparticles, and Phosphatidylserine (PS)-positive platelets detected by flow cytometry. Platelet aggregation (induced by collagen/ristocetin) was measured by Lumi-aggregometry. Platelet receptors were shed after exposure to NPSS showing a positive correlation with the level of shear stress. The generation of platelet microparticles and PS-positive platelets also increased with greater NPSS. Elevated NPSS decreased the platelet aggregation capacity. Platelet activation level increased with greater NPSS. Being treated by thrombin can further exacerbate these characteristics under same level of NPSS, except that platelet activation level drastically dropped after the exposure to 175 Pa NPSS in the thrombin-treated blood. After being treated by thrombin, platelets became more susceptible to NPSS, resulting in more receptor shedding, platelet microparticles, and PS-positive platelets, thus limiting platelet aggregation capacity after exposure to NPSS. Platelet activation, in terms of PAC-1 and P-selectin, is an interim status competing between the expression and shedding of these makers/receptors. When platelets have reached a saturation level of activation, exposure to excessive NPSS can potentially impair activation. [ABSTRACT FROM AUTHOR]

Background: Left ventricular assist devices (LVADs) have been used as a standard treatment option for patients with advanced heart failure. However, these devices are prone to adverse events. Nonsurgical bleeding (NSB) is the most common complication in patients with continuous flow (CF) LVADs. The development of acquired von Willebrand syndrome (AVWS) in CF‐LVAD recipients is thought to be a key factor. However, AVWS is seen across a majority of LVAD patients, not just those with NSB. The purpose of this study was to examine the link between acquired platelet defects and NSB in CF‐LVAD patients. Methods: Blood samples were collected from 62 CF‐LVAD patients at pre‐ and 4 post‐implantation timepoints. Reduced adhesion receptor expression (GPIbα and GPVI) and activation of platelets (GPIIb/IIIa activation) were used as markers for acquired platelet defects. Results: Twenty‐three patients experienced at least one NSB episode. Significantly higher levels of platelet activation and receptor reduction were seen in the postimplantation blood samples from bleeders compared with non‐bleeders. All patients experienced the loss of high molecular weight monomers (HMWM) of von Willebrand Factor (vWF), but no difference was seen between the two groups. Multivariable logistic regression showed that biomarkers for reduced platelet receptor expression (GPIbα and GPVI) and activation (GPIIb/IIIa) have more predictive power for NSB, with the area under curve (AUC) values of 0.72, 0.68, and 0.62, respectively, than the loss of HMWM of vWF (AUC: 0.57). Conclusion: The data from this study indicated that the severity of acquired platelet defects has a direct link to NSB in CF‐LVAD recipients. [ABSTRACT FROM AUTHOR]

Shear-induced platelet activation is one of the critical outcomes when blood is exposed to elevated shear stress. Excessively activated platelets in the circulation can lead to thrombus formation and platelet consumption, resulting in serious adverse events such as thromboembolism and bleeding. While experimental observations reveal that it is related to the shear stress level and exposure time, the underlying mechanism of shear-induced platelet activation is not fully understood. Various models have been proposed to relate shear stress levels to platelet activation, yet most are modified from the empirically calibrated power-law model. Newly developed multiscale platelet models are tested as a promising approach to capture a single platelet's dynamic shape during activation, but it would be computationally expensive to employ it for a large-scale analysis. This paper summarizes the current numerical models used to study the shear-induced platelet activation and their computational applications in the risk assessment of a particular flow pattern and clot formation prediction. [ABSTRACT FROM AUTHOR]

Background: Sheep are a primary model of mechanical circulatory support (MCS) with heparin anticoagulation therapy frequently being monitored by activated clotting time (ACT) due to ease and cost. In patients undergoing long‐term heparin therapy, other anticoagulation monitoring strategies, such as activated partial thromboplastin time (aPTT), have proven to be more reliable indicators for the adequacy of anticoagulation, frequently determined by heparin concentration. As there is a paucity of similar studies in sheep, we sought to investigate the correlation between heparin concentration and ACT and aPTT using whole sheep blood in an ex vivo model. Methods: Fresh whole blood was serially drawn from an adult female Dorset‐hybrid sheep and aliquots were placed into tubes containing heparin saline solutions with concentrations ranging from 0 to 7.81 U heparin per mL of whole blood. ACT and aPTT values were measured on each of the samples. The experiment was performed four times with the same animal. A simple linear regression was performed to determine correlation, and subgroup analysis was performed on low versus high heparin concentrations typically seen in human patients on long‐term MCS, such as extracorporeal membrane oxygenation (ECMO), versus cardiopulmonary bypass, respectively. Results: aPTT measurements versus the heparin concentration had an R2 = 0.7295. ACT measurements versus the heparin concentration had a R2 = 0.4628. aPTT measurements versus the ACT measurements had a R2 = 0.2974. The strength of the correlation between aPTT and heparin concentration increased at low heparin concentrations (R2 = 0.8392). Conclusion: aPTT had a more reliable correlation to heparin concentration and thus anticoagulation level than ACT. This was particularly true at lower heparin concentrations, similar to ranges seen for patients on ECMO. The correlation between aPTT and ACT values was poor. Further in vivo studies should be performed to confirm our results. [ABSTRACT FROM AUTHOR]

We read with interest the article by Granja et al ([1]), published in the recent issue of I Critical Care Medicine i , on multi-modal characterization of extracorporeal membrane oxygenation (ECMO)-induced coagulopathy (EIC). Both the platelet glycoprotein (GP)1b receptor and von Willebrand factor (VWF) play an important role in localizing platelets to a site of vascular injury. [Extracted from the article]

Objective: Leukocytes play an important role in the body's immune system. The aim of this study was to assess alterations in neutrophil phenotype and function in pump‐assisted circulation in vitro. Methods: Human blood was circulated for four hours in three circulatory flow loops with a CentriMag blood pump operated at a flow of 4.5 L/min at three rotational speeds (2100, 2800, and 4000 rpm), against three pressure heads (75, 150, and 350 mm Hg), respectively. Blood samples were collected hourly for analyses of neutrophil activation state (Mac‐1, CD62L, CD162), neutrophil reactive oxygen species (ROS) production, apoptosis, and neutrophil phagocytosis. Results: Activated neutrophils indicated by both Mac‐1 expression and decreased surface expression of CD62L and CD162 receptors increased with time in three loops. The highest level of neutrophil activation was observed in the loop with the highest rotational speed. Platelet‐neutrophil aggregates (PNAs) progressively increased in two loops with lower rotational speeds. PNAs peaked at one hour after circulation and decreased subsequently in the loop with the highest rotational speed. Neutrophil ROS production dramatically increased at one hour after circulation and decreased subsequently in all three loops with similar levels and trends. Apoptotic neutrophils increased with time in all three loops. Neutrophil phagocytosis capacity in three loops initially elevated at one hour after circulation and decreased subsequently. Apoptosis and altered phagocytosis were dependent on rotational speed. Conclusions: Our study revealed that the pump‐assisted circulation induced neutrophil activation, apoptosis, and functional impairment. The alterations were strongly associated with pump operating condition and duration. [ABSTRACT FROM AUTHOR]

High mechanical shear stresses (HMSS) can cause damage to blood, which manifests as morphologic changes, shortened life span, biochemical alterations, and complete rupture of blood cells and proteins, leading to the alterations of normal blood function. The aim of this study is to determine the state of neutrophil activation and function alterations caused by HMSS with short exposure time relevant to ventricular assist devices. Blood from healthy donors was exposed to three levels of HMSS (75Pa, 125Pa, and 175Pa) for a short exposure time (0.5 s) using our Couette‐type blood‐shearing device. Neutrophil activation (Mac‐1, platelet‐neutrophil aggregates) and surface expression levels of two key functional receptors (CD62L and CD162) on neutrophils were evaluated by flow cytometry. Neutrophil phagocytosis and transmigration were also examined with functional assays. Results showed that the expression of Mac‐1 on neutrophils and platelet‐neutrophil aggregates increased significantly while the level of CD62L expression on neutrophils decreased significantly after the exposure to HMSS. The Mac‐1 expression progressively increased while the CD62L expression progressively decreased with the increased level of HMSS. The level of CD162 expression on neutrophils slightly increased after the exposure to HMSS, but the increase was not significant. The phagocytosis assay data revealed that the ability of neutrophils to phagocytose latex beads coated with fluorescently labeled rabbit IgG increased significantly with the increased level of HMSS. The transmigration ability of neutrophils slightly increased after the exposure to HMSS, but did not reach a significant level. In summary, HMSS with a short exposure time of 0.5 seconds could induce neutrophil activation, platelet‐neutrophil aggregation, shedding of CD62L receptor, and increased phagocytic ability. However, the exposure to the three levels of HMSS did not cause a significant change in neutrophil transmigration capacity and shedding of CD162 receptor on neutrophils. [ABSTRACT FROM AUTHOR]

This work introduces a new Lagrangian strain‐based model to predict the shear‐induced hemolysis in biomedical devices. Current computational models for device‐induced hemolysis usually utilize empirical fitting of the released free hemoglobin (Hb) in plasma from damaged red blood cells (RBCs). These empirical correlations contain parameters that depend on specific device and operating conditions, thus cannot be used to predict hemolysis in a general device. The proposed algorithm does not have any empirical parameters, thus can presumably be used for hemolysis prediction in various blood‐wetting medical devices. In contrast to empirical correlations in which the Hb release is related to the shear stress and exposure time without considering the physical processes, the proposed model links flow‐induced deformation of the RBC membrane to membrane permeabilization and Hb release. In this approach, once the steady‐state numerical solution of blood flow in the device is obtained under a prescribed operating condition, sample path lines are traced from the inlet of the device to the outlet to calculate the history of the shear stress tensor. In solving the fluid flow, it is assumed that RBCs do not have any influence on the flow pattern. Along each path line, shear stress tensor will be input into a coarse‐grained (CG) RBC model to calculate the RBC deformation. Then the correlations obtained from molecular dynamics (MD) simulations are applied to relate the local areal RBC deformation to the perforated area on the RBC membrane. Finally, Hb released out of transient pores is calculated over each path line via a diffusion equation considering the effects of the steric hindrance and increased hydrodynamic drag due to the size of the Hb molecule. The total index of hemolysis (IH) is calculated by integration of released Hb over all the path lines in the computational domain. Hemolysis generated in the Food and Drug Administration (FDA) nozzle and two blood pumps, that is, a CentriMag blood pump (a centrifugal pump) and HeartMate II (an axial pump), for different flow regimes including the laminar and turbulent flows are calculated via the proposed algorithm. In all the simulations, the numerical predicted IH is close to the range of experimental data. The results promisingly indicate that this multiscale approach can be used as a tool for predicting hemolysis and optimizing the hematologic design of other types of blood‐wetting devices. [ABSTRACT FROM AUTHOR]

The regions with high non-physiological shear stresses (NPSS) are inevitable in blood-contacting medical devices (BCMDs) used for mechanically assisted circulatory support. NPSS can cause platelet activation and receptor shedding potentially resulting in the alteration of hemostatic function. In this study, we developed a dissipative particle dynamics model to characterize clot formation (platelet–collagen and inter-platelet adhesion) of NPSS-traumatized blood at a vascular injury site. A rectangular tube of 50 × 50 × 200 µm with an 8 × 8 µm collagen-coated area was modeled as a small blood vessel and perfusion with blood. Clot formation dynamics during perfusion was simulated. NPSS-traumatized blood was modeled to have more activated platelet and fewer adhesion receptors with weakened inter-platelet binding. Computational results showed that clots grew at a faster rate while the structure of the clots was less stable and collapsed more frequently for NPSS-traumatized blood compared with normal blood. The finding that NPSS-traumatized platelets could result in quicker but more easily breakable blood clots at injury sites may explain why increased risks of thrombotic and bleeding complications occurred concurrently in patients implanted with BCMDs. [ABSTRACT FROM AUTHOR]

The roles of the large membrane surface of the oxygenator and the high mechanical shear stress (HMSS) of the pump in the extracorporeal membrane oxygenation (ECMO) circuit were examined under a pediatric support setting. A clinical centrifugal pump and a pediatric oxygenator were used to construct the ECMO circuit. An identical circuit without the oxygenator was constructed for comparison. Fresh human blood was circulated in the two circuits for 4 hours under the identical pump speed and flow. Blood samples were collected hourly for blood damage assessment, including platelet activation, generation of platelet‐derived microparticles (PDMP), losses of key platelet hemostasis receptors (glycoprotein (GP) Ibα (GPIbα) and GPVI), and high molecular weight multimers (HMWM) of von Willebrand factor (VWF) and plasma free hemoglobin (PFH). Platelet adhesion on fibrinogen, VWF, and collagen was further examined. The levels of platelet activation and generation of PDMP and PFH exhibited an increasing trend with circulation time while the expression levels of GPIbα and GPVI receptors on the platelet surface decreased. Correspondingly, the platelets in the blood samples exhibited increased adhesion capacity to fibrinogen and decreased adhesion capacities on VWF and collagen with circulation time. Loss of HMWM of VWF occurred in both circuits. No statistically significant differences were found in all the measured parameters for blood damage and platelet adhesion function between the two circuits. The results indicate that HMSS from the pump played a dominant role in blood damage associated with ECMO and the impact of the large surface of the oxygenator on blood damage was insignificant. [ABSTRACT FROM AUTHOR]

The ability of current renal replacement therapy modalities to achieve rapid solute removal is limited by membrane surface area and blood flow rate. Extracorporeal membrane oxygenation offers high blood flow and hemodynamic support that may be harnessed to overcome limitations in traditional renal replacement therapy. Using an extracorporeal membrane oxygenation circuit, we describe a high blood flow, high-efficiency hemofiltration technique using in-line hemofilters (hemoconcentrators) and standard replacement fluid to enhance solute clearance. Using this approach and a total of 5 L of replacement volume per treatment, creatinine (Cr) clearances of 8.3 L/hour and 11.2 L/hour using one and two hemoconcentrators, respectively, were achieved. With use of a high blood flow rate of up to 5 L/min, this hemofiltration technique can potentially offer clearance of 30 times that of continuous renal replacement therapy and of 6 times that of hemodialysis which may expand the ability to remove substances traditionally not considered removable via existing extracorporeal therapies. [ABSTRACT FROM AUTHOR]

Extracorporeal membrane oxygenation (ECMO) has become a mainstay of therapy for patients suffering from severe respiratory failure. Ambulatory ECMO systems aim to provide long‐term out‐of‐hospital respiratory support. As a patient's activity level changes, the required level of ECMO support varies with oxygen consumption and metabolic fluctuations. To compensate for such changes, an autoregulatory ECMO system (AR‐ECMO) has been developed and its performance was evaluated as a proof of concept in an acute ovine model. The AR‐ECMO system consists of a regular ECMO circuit and an electromechanical control system. A custom fuzzy logic control algorithm was implemented to adjust the blood flow and sweep gas flow of the ECMO circuit to meet the varying respiratory demand by utilizing two noninvasive sensors for venous oxyhemoglobin saturation and the oxygenator exhaust gas CO2 concentration. Disturbance responses of the AR‐ECMO to induced acute respiratory distress were assessed for six hours in four juvenile sheep cannulated with a veno‐pulmonary artery ECMO configuration, including acute ventilator shutoff, ventilator step change (off‐on‐off), and forced desaturation. All sheep survived for the study duration. The AR‐ECMO system was able to respond and maintain stable hemodynamics and physiological blood gas contents (SpO2 = 96.3 % ± 4.29, pH 7.44 ± 0.09, pCO2 = 38.9 ± 9.9 mm Hg, and pO2 =237.9 ± 123.6 mm Hg) during simulated respiratory distress. Acceptable correlation between oxygenator exhaust gas CO2 and oxygenator outlet pCO2 were observed (R2 = 0.84). In summary, the AR‐ECMO system successfully maintained physiologic control of peripheral oxygenation and carbon dioxide over the study period, utilizing only measurements taken directly from the ECMO circuit. The range of system response necessitates an adaptable system in the setting of variable metabolic demands. The ability of this system to respond to significant disturbances in ventilator support is encouraging. Future work to evaluate our AR‐ECMO system in long‐term, awake animal studies is necessary for further refinement. [ABSTRACT FROM AUTHOR]

The aim of this study was to examine the impact of the nonphysiological shear stress (NPSS) on platelet hemostatic function relevant to thrombosis and bleeding in mechanically assisted circulation. Fresh human blood was circulated for four hours in in vitro circulatory flow loops with a CentriMag blood pump operated under a flow rate of 4.5 L/min against three pressure heads (70 mm Hg, 150 mm Hg, and 350 mm Hg) at 2100, 2800, and 4000 rpm, respectively. Hourly blood samples from the CentriMag pump‐assisted circulation loops were collected and analyzed for glycoprotein (GP) IIb/IIIa activation and receptor shedding of GPVI and GPIbα on the platelet surface with flow cytometry. Adhesion of platelets to fibrinogen, collagen, and von Willebrand factor (VWF) of the collected blood samples was quantified with fluorescent microscopy. In parallel, mechanical shear stress fields within the CentriMag pump operated under the three conditions were assessed by computational fluid dynamics (CFD) analysis. The experimental results showed that levels of platelet GPIIb/IIIa activation and platelet receptor shedding (GPVI and GPIbα) in the blood increased with increasing the circulation time. The levels of platelet activation and loss of platelet receptors GPVI and GPIbα were consistently higher with higher pressure heads at each increasing hour in the CentriMag pump‐assisted circulation. The platelet adhesion on fibrinogen increased with increasing the circulation time for all three CentriMag operating conditions and was correlated well with the level of platelet activation. In contrast, the platelet adhesion on collagen and VWF decreased with increasing the circulation time under all the three conditions and was correlated well with the loss of the receptors GPVI and GPIbα on the platelet surface, respectively. The CFD results showed that levels of shear stresses inside the CentriMag pump under all three operating conditions exceeded the maximum level of shear stress in the normal physiological circulation and were strongly dependent on the pump operating condition. The level of platelet activation and loss of key platelet adhesion receptors (GPVI and GPIbα) were correlated with the level of NPSS generated by the CentriMag pump, respectively. In summary, the level of NPSS associated with pump operating condition is a critical determinant of platelet dysfunction in mechanically assisted circulation. [ABSTRACT FROM AUTHOR]

In vitro hemolysis testing remains one of the most important performance measures to judge the hemocompatibility of a left ventricular assist device (LVAD). Clinically relevant operating conditions and appropriate testing blood are essential to infer in vitro data for potential clinical use. This in vitro study was carried out to evaluate and compare the hemolytic performance of a newly developed magnetically levitated (maglev) LVAD (CH‐VAD) with two clinically used LVADs (HVAD and HeartMate II (HMII)) using fresh human blood. A small volume (~300 mL) in vitro circulating flow loop was constructed with a LVAD generated flow of 4.5 L/min at the nominal or reported clinical operating speed for each LVAD. The blood was circulated in the loop for 4 hours with samples drawn at baseline and hourly. Plasma‐free hemoglobin (PFH) concentrations in the hourly blood samples were determined with spectrophotometry. Normalized index of hemolysis (NIH) was calculated to compare the hemolytic performance of the CH‐VAD and the two reference LVADs. Platelet activation was measured with flow cytometry. The experimental test for each device was repeated at least 7 times. The data from this study showed that all the three LVADs generated very low hemolysis (NIH <0.01 g/100 L). The CH‐VAD was found to have a significantly lower NIH value (0.00135 ± 0.00032 g/100 L) compared to the HVAD (0.00525 ± 0.00183 g/100 L) and the HMII (0.00583 ± 0.00182 g/100 L). No statistically significant difference in device‐generated hemolysis was found between the HVAD and the HMII. The level of platelet activation induced by the CH‐VAD is significantly lower than those by the HVAD and the HMII. The data suggest that the shear‐induced hemolysis and platelet activation of the CH‐VAD are acceptable relative to the two LVADs currently in clinical use. [ABSTRACT FROM AUTHOR]

The PI3K/Akt signaling pathway has been implicated in playing an important role in platelet activation during hemostasis and thrombosis involving platelet‐matrix interaction and platelet aggregation. Its role in non‐physiological shear stress (NPSS)‐induced platelet activation relevant to high‐shear blood contacting medical devices (BCMDs) is unclear. In the context of blood cells flowing in BCMDs, platelets are subjected to NPSS (>100 Pa) with very short exposure time (<1 s). In this study, we investigated whether NPSS with short exposure time induces platelet activation through the PI3K/Akt signaling pathway. Healthy donor blood treated with or without PI3K inhibitor was subjected to NPSS (150 Pa) with short exposure time (0.5 s). Platelet activation indicated by the surface P‐selectin expression and activated glycoprotein (GP) IIb/IIIa was quantified using flow cytometry. The phosphorylation of Akt, activation of the PI3K signaling, was characterized by western blotting. Changes in adhesion behavior of NPSS‐sheared platelets on fibrinogen, collagen, and von Willebrand factor (vWF) were quantified with fluorescent microscopy by perfusing the NPSS‐sheared and PI3K inhibitor‐treated blood through fibrinogen, collagen, and vWF‐coated microcapillary tubes. The results showed that the PI3K/Akt signaling was involved with both NPSS‐induced platelet activation and platelet‐matrix interaction. NPSS‐sheared platelets exhibited exacerbated platelet adhesion on fibrinogen, but had diminished platelet adhesion on collagen and vWF. The inhibition of PI3K signaling reduced P‐selectin expression and GPIIb/IIIa activation with suppressed Akt phosphorylation and abolished NPSS‐enhanced platelet adhesion on fibrinogen in NPSS‐sheared blood. The inhibition of PI3K signaling can attenuate the adhesion of unsheared platelets (baseline) on collagen and vWF, while had no impact on adhesion of NPSS‐sheared platelets on collagen and vWF. This study confirmed the important role of PI3K/Akt signaling pathway in NPSS‐induced platelet activation. The finding of this study suggests that blocking PI3K/Akt signaling pathway could be a potential method to treat thrombosis in patients implanted with BCMDs. [ABSTRACT FROM AUTHOR]

Thrombotic and bleeding complications are the major obstacles for expanding mechanical circulatory support (MCS) beyond the current use. While providing the needed hemodynamic support, those devices can induce damage to blood, particularly to platelets. In this study, we investigated device‐induced alteration of three major platelet surface receptors, von Willebrand factor (VWF) and associated hemostatic functions relevant to thrombosis and bleeding. Fresh human whole blood was circulated in an extracorporeal circuit with a clinical rotary blood pump (CentriMag, Abbott, Chicago, IL, USA) under the clinically relevant operating condition for 4 hours. Blood samples were examined every hour for glycoprotein (GP) IIb/IIIa activation and receptor loss of GPVI and GPIbα on the platelet surface with flow cytometry. Soluble P‐selectin in hourly collected blood samples was measured by enzyme linked immunosorbent assay to characterize platelet activation. Adhesion of device‐injured platelets to fibrinogen, collagen, and VWF was quantified with fluorescent microscopy. Device‐induced damage to VWF was characterized with western blotting. The CentriMag blood pump induced progressive platelet activation with blood circulating time. Particularly, GPIIb/IIIa activation increased from 1.1% (Base) to 11% (4 hours) and soluble P‐selectin concentration increased from 14.1 ng/mL (Base) to 26.5 ng/mL (4 hours). Those device‐activated platelets exhibited increased adhesion capacity to fibrinogen. Concurrently, the CentriMag blood pump caused progressive platelet receptor loss (GPVI and GPIbα) with blood circulating time. Specifically, MFI of the GPVI and GPIbα receptors decreased by 17.2% and 16.1% for the 4‐hours sample compared to the baseline samples, respectively. The device‐injured platelets exhibited reduced adhesion capacities to collagen and VWF. The high molecular weight multimers (HMWM) of VWF in the blood disappeared within the first hour of the circulation. Thereafter the multimeric patterns of VWF were stable. The change in the VWF multimeric pattern was different from the progressive structural and functional changes of platelets with the circulation time. This study suggested that the CentriMag blood pump could induce two opposite effects on platelets and associated hemostatic functions under a clinically relevant operating condition. The device‐altered hemostatic function may contribute to thrombosis and bleeding simultaneously as occurring in patients supported by a rotary blood pump. Device‐induced damage of platelets may be an important cause for bleeding in patients supported with rotary blood pump MCS systems relative to device‐induced loss of HMWM‐VWF. [ABSTRACT FROM AUTHOR]

Modulation of pump speed has been proposed and implemented clinically to improve vascular pulsatility in continuous flow ventricular assist device patient. The flow dynamics of the HVAD with a promising asynchronous pump speed modulation and its potential risk for device-induced blood trauma was investigated numerically. The boundary conditions at the pump inlet and outlet were defined using the pressure waveforms adapted from the experimentally recorded ventricular and arterial pressure waveforms in a large animal ischemic heart failure (IHF) model supported by the HVAD operated at constant and modulated pump speeds. Shear stress fields and hemolysis indices were derived from the simulated flow fields. The overall features of the computationally generated flow waveforms at simulated constant and pulse-modulated speed operations matched with those of the experimentally recorded flow waveforms. The simulations showed that the shear stress field and hemolysis index vary throughout the cardiac cycle under the constant speed operation, and also as a function of modulation profile under modulated speed operation. The computational model did not demonstrate any differences in the time average hemolysis index between constant and modulated pump speed operations, thereby predicting pulse-modulated speed operation may help to restore vascular pulsatility without any further increased risk of blood trauma. Graphical abstract The streamline inside the HVAD pump and the wall shear stress distribution on the impeller surface at six discrete time instants over one cardiac cycle under constant speed operation (3000 rpm) (a) and under pulse-modulated speed operation (b). c Computationally predicted flow rate waveform under pulse-modulated speed operation. d Computationally predicted time-varying HI generated by the HVAD pump under the two operation modes constant speed (dash line) and pulse-modulated speed (solid line). These figures indicate that the pulse-modulated speed operation may help to restore vascular pulsatility without any further increased risk of blood trauma. [ABSTRACT FROM AUTHOR]

Abstract: In this study, the flow features and device‐associated blood trauma in 4 clinical ventricular assist devices (VADs; 2 implantable axial VADs, 1 implantable centrifugal VAD, and 1 extracorporeal VAD) were computationally analyzed under clinically relevant pulsatile flow conditions. The 4 VADs were operated at fixed pump speed at a mean rate of 4.5 L/min. Mean pressure difference, wall shear stress, volume distribution of scalar shear stress (SSS), and shear‐induced hemolysis index (HI) were derived from the flow field of each VAD and were compared. The computationally predicted mean pressure difference across the 3 implantable VADs was ~70 mmHg, and the extracorporeal VAD was ~345 mmHg, which matched well with their reported pressure‐flow curves. The axial VADs had higher mean wall shear stress and SSS compared with the centrifugal VADs. However, the residence time of the centrifugal VADs was much longer compared with the axial VADs because of the large volume of the centrifugal VADs. The highest SSS was observed in one axial VAD, and the longest exposure time was observed in 1 centrifugal VAD. These 2 VADs generated the highest HI. The shear‐induced HI varied as a function of flow rate within each cardiac cycle. At fixed pump speed, the HI was greatest at low flow rate due to longer exposure time to shear stress compared with at high flow rate. Subsequently, we hypothesize that to reduce the risk of blood trauma during VAD support, shear stress magnitude and exposure time need to be minimized. [ABSTRACT FROM AUTHOR]

Introduction Oxidative stress and platelet integrin α2bβ3 plays important role in the process of hemostasis and thrombosis. We hypothesized that device-induced patient specific oxidative stress and integrin α2bβ3 shedding may be linked to major bleeding complication (MBC) in heart failure (HF) patients supported by continuous flow left ventricular assist devices (CF-LVADs). Materials and methods We recruited 47patients implanted with CF-LVADs and 15 healthy volunteers. Fourteen patients developed MBC (bleeder group) within one month after implantation while others were considered non-bleeder group (n = 33). Oxidative stresses were evaluated by measuring reactive oxygen species (ROS) in platelets, superoxide dismutase (SOD) activity, total antioxidant capacity (TAC) and oxidized low density lipoprotein (oxLDL). Assessments of α2bβ3 were carried out using flow cytometry and ELISA. Results Biomarkers of oxidative stress and α2bβ3 shedding (decreased surface expression and higher plasma levels) were found to be preexisting condition in all HF patients prior to CF-LVAD implantation compared to the healthy volunteers. Significantly elevated levels of ROS and oxLDL; concomitant depletion of SOD and TAC; and α2bβ3 shedding were observed in the bleeder group temporarily in comparison to the non-bleeder group after CF-LVAD implantation. A significantly strong association between α2bβ3 shedding and biomarkers of oxidative stress was observed; suggesting a potential role of oxidative stress in platelet integrin shedding leading to MBC after CF-LVAD implantation. Moreover, a receiver operating characteristic (ROC) analysis indicated that the likelihood of MBC data from Integrin α2bβ3 shedding had a predictive power of MBC in CF-LVAD patients. Conclusions Oxidative stress might play a potential role in accelerating α2bβ3 shedding and platelet dysfunction, resulting in MBC in CF-LVAD patients. Integrin α2bβ3 shedding may be used to refine bleeding risk stratification in CF-LVAD patients. [ABSTRACT FROM AUTHOR]

Respiratory failure is one of the major causes of mortality and morbidity all over the world. Therapeutic options to treat respiratory failure remain limited. The objective of this study was to evaluate the gas transfer performance of a newly developed miniature portable integrated pediatric pump-lung device (PediPL) with small membrane surface for respiratory support in an acute ovine respiratory failure model. The respiratory failure was created in six adult sheep using intravenous anesthesia and reduced mechanical ventilation at 2 breaths/min. The PediPL device was surgically implanted and evaluated for respiratory support in a venovenous configuration between the right atrium and pulmonary artery. The hemodynamics and respiratory status of the animals during support with the device gas transfer performance of the PediPL were studied for 4 h. The animals exhibited respiratory failure 30 min after mechanical ventilation was reduced to 2 breaths/min, indicated by low oxygen partial pressure, low oxygen saturation, and elevated carbon dioxide in arterial blood. The failure was reversed by establishing respiratory support with the PediPL after 30 min. The rates of O2 transfer and CO2 removal of the PediPL were 86.8 and 139.1 mL/min, respectively. The results demonstrated that the PediPL (miniature integrated pump-oxygenator) has the potential to provide respiratory support as a novel treatment for both hypoxia and hypercarbia. The compact size of the PediPL could allow portability and potentially be used in many emergency settings to rescue patients suffering acute lung injury. [ABSTRACT FROM AUTHOR]

Blood can become hypercoagulable by shear-induced platelet activation and generation of microparticles. It has been reported that nonphysiological shear stress (NPSS) could induce shedding of platelet receptor glycoprotein (GP) Iba, which may result in an opposite effect to hemostasis. The aim of this study was to investigate the influence of the NPSS on platelets and von Willebrand factor (vWF). Human blood was exposed to two levels of NPSS (25 Pa, 125 Pa) with an exposure time of 0.5 s, generated by using a novel blood-shearing device. Platelet activation (P-selectin expression, GPIIb/IIIa activation and generation of microparticles) and shedding of three platelet receptors (GPIbα, GPVI, GPIIb/IIIa) in sheared blood were quantified using flow cytometry. Aggregation capacity of sheared blood induced by ristocetin and collagen was evaluated using an aggregometer. Shear-induced vWF damage was characterized with Western blotting. Consistent with the published data, the NPSS caused significantly more platelets to become activated with increasing NPSS level. Meanwhile, the NPSS induced the shedding of platelet receptors. The loss of the platelet receptors increased with increasing NPSS level. The aggregation capacity of sheared blood induced by ristocetin and collagen decreased. There was a loss of high molecular weight multimers (HMWMs) of vWF in sheared blood. These results suggest that the NPSS induced a paradoxical effect. More activated platelets increase the risk of thrombosis, while the reduction in platelet receptors and the loss of HMWM-vWF increased the propensity of bleeding. The finding might provide a new perspective to understand thrombosis and acquired bleeding disorder in patients supported with blood contacting medical devices. [ABSTRACT FROM AUTHOR]

The role of oxidative stress and leukocyte activation has not been elucidated in developing systemic inflammatory response syndrome ( SIRS) in heart failure ( HF) patients after continuous-flow left ventricular assist device ( CF-LVAD) implantation. The objective of this study was to investigate the change of plasma redox status and leukocyte activation in CF-LVAD implanted HF patients with or without SIRS. We recruited 31 CF-LVAD implanted HF patients (16 SIRS and 15 non- SIRS) and 11 healthy volunteers as the control. Pre- and postimplant blood samples were collected from the HF patients. Plasma levels of oxidized low-density lipoprotein ( oxLDL), malondialdehyde ( MDA), total antioxidant capacity ( TAC), superoxide dismutase ( SOD) in erythrocyte, myeloperoxidase ( MPO), and polymorphonuclear elastase ( PMN-elastase) were measured. The HF patients had a preexisting condition of oxidative stress than healthy controls as evident from the higher oxLDL and MDA levels as well as depleted SOD and TAC. Leukocyte activation in terms of higher plasma MPO and PMN-elastase was also prominent in HF patients than controls. Persistent oxidative stress and reduced antioxidant status were found to be more belligerent in HF patients with SIRS after the implantation of CF-LVAD when compared with non- SIRS patients. Similar to oxidative stress, the activation of blood leukocyte was significantly highlighted in SIRS patients after implantation compared with non- SIRS. We identified that the plasma redox status and leukocyte activation became more prominent in CF-LVAD implanted HF patients who developed SIRS. Our findings suggest that plasma biomarkers of oxidative stress and leukocyte activation may be associated with the development of SIRS after CF-LVAD implant surgery. [ABSTRACT FROM AUTHOR]

The scarcity of donor organs has led to the development of devices that provide optimal long-term respiratory or cardiopulmonary support to bridge recipients as they wait for lung and/or heart transplantation. This study was designed to evaluate the 30-day in vivo performance of the newly developed pediatric pump-lung ( PediPL) for cardiopulmonary support using a juvenile sheep model. The PediPL device was placed surgically between the right atrium and descending aorta in eight sheep (25.4-31.2 kg) and evaluated for 30 days. Anticoagulation was maintained with continuous heparin infusion (activated clotting time 150-200 s). The flow rate was measured continually, and gas transfer was measured daily. Plasma free hemoglobin, platelet activation, hematologic data, and blood biochemistry were assessed twice a week. Sheep were euthanized after 30 days. The explanted devices were examined for gross thrombosis. Six sheep survived for 30-32 days. During the study, the oxygen transfer rate of the devices was 54.9 ± 13.2 mL/min at a mean flow rate of 1.14 ± 0.46 L/min with blood oxygen saturation of 95.4% ± 1.7%. Plasma free hemoglobin was 8.2 ± 3.7 mg/dL. Platelet activation was 5.35 ± 2.65%. The animals had normal organ chemistries except for surgery-related transient alterations in kidney and liver function. Although we found some scattered thrombi on the membrane surfaces of some explanted devices during the necropsy, the device function and performance did not degrade. The PediPL device was capable of providing cardiopulmonary support with long-term reliability and good biocompatibility over the 30-day duration and offers the potential option for bridging pediatric patients with end-stage heart or lung disease to heart and/or lung transplantation. [ABSTRACT FROM AUTHOR]

The surviving myocardium initially compensates the loss of injured myocardium after myocardial infarction (MI) and gradually becomes progressively dysfunctional. There have been limited studies on the effect of infarct size on temporal and spatial alterations in the myocardium during progressive myocardial remodeling. MI with three infarct sizes, i.e. 15, 25 and 35% of the left ventricular (LV) wall, was created in an ovine infarction model. The progressive LV remodeling over a 12-week period was studied. Echocardiography, sonomicrometry, and histological and molecular analyses were carried out to evaluate cardiac function, regional tissue contractile function, structural remodeling and cardiomyocyte hypertrophy, and calcium handling proteins. Twelve weeks after MI, the 15, 25 and 35% MI groups had normalized LV end diastole volumes of 1.4 ± 0.2, 1.7 ± 0.3 and 2.0 ± 0.4 ml/kg, normalized end systole volumes of 1.0 ± 0.1, 1.0 ± 0.2 and 1.3 ± 0.3 ml/kg and LV ejection fractions of 43 ± 3, 42 ± 6 and 34 ± 4%, respectively. They all differed from the sham group (p < 0.05). All the three MI groups exhibited larger wall areal expansion (remodeling strain), larger cardiomyocyte size and altered expression of calcium handing proteins in the adjacent myocardium compared to the remote counterpart from the infarct. A significant correlation was found between cardiomyocyte size and remodeling strain in the adjacent zone. A comparative analysis among the three MI groups showed that a larger infarct size (35 vs. 15% MI) was associated with larger remodeling strain, more serious impairment in the cellular structure and composition, and regional contractile function at regional tissue level and LV function at organ level. © 2015 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]

Non-surgical bleeding (NSB) is the most common clinical complication among heart failure (HF) patients supported by continuous-flow left ventricular assist devices (CF-LVADs). Understanding the role of platelet functionality contributing to NSB after CF-LVAD implantation is crucial for prevention and management of this adverse event. The aim of this study was to examine the role of intraplatelet reactive oxygen species (ROS) and platelet damage on the incidence of bleeding events after CF-LVAD implantation in HF patients. We recruited 25 HF patients implanted with CF-LVADs and 11 healthy volunteers as the control. Intraplatelet ROS generation, platelet mitochondrial damage and platelet apoptosis were quantified by flow cytometry. Among 25 patients, 8 patients developed non-surgical bleeding within one month after CF-LVAD implantation. Intraplatelet ROS, depolarized and apoptotic platelet were found to be pre-existing conditions in all baseline samples of the 25 HF patients when compared to the healthy volunteers. There was no significant difference in the levels of ROS between the non-bleeder and the bleeder groups prior to CF-LVAD implantation, although we noticed 2-fold and 1.5-fold rise in depolarized and apoptotic platelets, respectively, in the bleeder group compared to those in the non-bleeder group. Post implant levels of intraplatelet ROS, depolarized and apoptotic platelets increased and remained elevated in the bleeder group, whereas periodic decreases were noticed in the non-bleeder group, suggesting the potential role of platelet damage on bleeding incidence. ROS generation after CF-LVAD implantation positively associated with platelet apoptosis (ρ = 0.4263,p = 0.0023) and depolarized platelets (ρ = 0.4774,p = 0.0002), especially the latter. In conclusion, elevated intraplatelet ROS and platelet damage may be linked to the NSB among HF patients supported by CF-LVAD. These results provide mechanistic insights into the bleeding complication in patients with CF-LVAD support. [ABSTRACT FROM PUBLISHER]

The nonphysiological mechanical shear stress in blood-contacting medical devices is one major factor to device-induced blood damage. Animal blood is often used to test device-induced blood damage potential of these devices due to its easy accessibility and low cost. However, the differences in shear-induced blood damage between animals and human have not been well characterized. The purpose of this study was to investigate shear-induced hemolysis of human and three commonly used preclinical evaluation animal species (ovine, porcine, and bovine) under shear conditions encountered in blood-contacting medical devices. Shear-induced hemolysis experiments were conducted using two single-pass blood-shearing devices. Driven by an externally pressurized reservoir, blood single-passes through a small annular gap in the shearing devices where the blood was exposed to a uniform high shear stress. Shear-induced hemolysis at different conditions of exposure time (0.04 to 1.5 s) and shear stress (25 to 320 Pa) was quantified for ovine, porcine, bovine, and human blood, respectively. Within these ranges of shear stress and exposure time, shear-induced hemolysis was less than 2% for the four species. The results showed that the ovine blood was more susceptible to shear-induced injury than the bovine, porcine, and human blood. The response of the porcine and bovine blood to shear was similar to the human blood. The dependence of hemolysis on shear stress level and exposure time was found to fit well the power law functional form for the four species. The coefficients of the power law models for the ovine, porcine, bovine, and human blood were derived. [ABSTRACT FROM AUTHOR]

Thrombosis and thromboembolism are the lifethreatening clinical complications for patients supported or treated with prosthetic cardiovascular devices. The high mechanical shear stress within these devices is believed to be the major contributing factor to cause platelet activation (PA) and function alteration, leading to thrombotic events. There have been limited quantitative data on how the high mechanical shear stress causes platelet activation. In this study, shear-induced PA in the ranges of well-defined shear stress and exposure time relevant to cardiovascular devices was quantitatively characterized for human blood using two novel flow-through Couette-type blood shearing devices. Four markers of platelet activation--surface Pselectin (CD62p), platelet-derived microparticles (PMPs), platelet-monocyte aggregation (PMA), and soluble P-selectin--were measured by flow cytometry and enzymelinked immunosorbent assay (ELISA), respectively. The results indicated that PA induced by high shear stresses with short exposure time could be reliably detected with surface P-selectin, and, to a lesser extent, PMPs rather than soluble P-selectin. It was also verified that PMA can be a highly sensitive indirect marker of platelet activation. The quantitative relationship between percentage of activated platelets indicated by surface P-selectin expression and shear stress/exposure time follows well the power law functional form. The coefficients of the power law models of PA based on surface P-selectin expression were derived. [ABSTRACT FROM AUTHOR]

Mesenchymal stem cells (MSCs) are currently undergoing testing in several clinical settings. The propagation of MSCs from multiple species in culture is an important step in furthering our understanding of these progenitor cells. Pim-1, a proto-oncogenic serine/threonine kinase, regulates cell proliferation, survival, and differentiation. Although it has been shown that Pim-1 participates in signal transduction mediating mitogenic action in MSCs, its roles in the modulation of MSC propagation remain to be defined. Understanding of ovine MSCs transduced with Pim-1 may provide improved ovine models for cellular therapy development. Using genetically modified ovine MSCs that constitutively overexpressed Pim-1 (MSC expressing PIM-1 and ZsGreen protein), we evaluated the impact of elevated Pim-1 activity on the proliferation, survival, and differentiation of MSCs in culture. Our results showed that Pim-1 enhanced the intrinsic molecular signals of growth and survival implicated in the mediation of serum signaling under normal culture conditions (10% serum). We found that Pim-1 promoted MSC proliferation irrespectively of the serum concentration, but with a decreased proliferation rate compared to increased serum concentrations, relative to the control vector-transduced MSC expressing ZsGreen protein. Further, Pim-1 prevented MSC apoptosis induced by hypoxia or serum deprivation as evidenced by enhanced mitochondria integrity and reduced annexin V binding. Interestingly, the phenotype and multilineage differentiation potential of the cells were not influenced by Pim-1. Taken together, these observations demonstrate that Pim-1 kinase cooperates with exogenous serum signals supporting MSC propagation in the ovine model. © 2014 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]

Background: Device availability of mechanical circulatory or respiratory support to the right heart has been limited. The purpose of this study was to investigate the effect of right heart unloading and respiratory support with a wearable integrated artificial pump-lung (APL). Methods: The APL device was placed surgically between the right atrium and pulmonary artery in 7 sheep. Anti-coagulation was performed with heparin infusion. The device's ability to unload the right ventricle (RV) was investigated by echocardiograms and right heart catheterization at different bypass flow rates. Hemodynamics and echocardiographic data were evaluated. APL flow and gas transfer rates were also measured at different device speeds. Results: Hemodynamics remained stable during APL support. There was no significant change in systemic blood pressure and cardiac index. Central venous pressure, RV pressure, RV end-diastolic dimension and RV ejection fraction were significantly decreased when APL device flow rate approached 2 liters/min. Linear regression showed significant correlative trends between the hemodynamic and cardiac indices and device speed. The oxygen transfer rate increased with device speed. The oxygen saturation from the APL outlet was fully saturated (>95%) during support. The impact of APL support on blood elements (plasma free hemoglobin and platelet activation) was minimal. Conclusions: APL device support significantly unloaded the RV with increasing device speed. The device also provided stable hemodynamics and respiratory support in terms of blood flow and oxygen transfer. The right heart unloading performance of this wearable device needs to be evaluated further in an animal model of right heart failure with long-term support. [ABSTRACT FROM AUTHOR]

Background: Non-surgical bleeding (NSB) is a major complication among heart failure (HF) patients supported by continuous-flow left ventricular assist devices (CF-LVADs). Understanding the hemostatic defects contributing to NSB after CF-LVAD implantation is crucial for prevention of this adverse event. The aim of this study was to examine the link between platelet glycoprotein Ibα (GPIbα) ectodomain shedding and NSB in CF-LVAD recipients and to identify a potential biomarker of NSB. Methods: Serial blood samples were collected from 35 HF patients supported with CF-LVADs. Platelet function was evaluated by a platelet function analysis device and thromboelastography (TEG). Platelet GPIbα shedding, von Willebrand factor (vWF) antigen and vWF collagen binding capacity were determined using enzyme-linked immunosorbent assays (ELISAs). The structural analysis of vWF was performed by gel electrophoresis. These platelet function measures with vWF parameters of the patients who had NSB between 4 and 32 days after CF-LVAD implantation (bleeder) were analyzed against those without NSB (non-bleeder). Blood samples from 7 healthy individuals were collected to obtain healthy reference values for the laboratory assays. Results: Elevated GPIbα shedding was found to be a pre-existing condition in all HF patients prior to CF-LVAD implantation. Post-operative level of GPIbα shedding increased and remained elevated in the bleeder group, whereas a consistent decrease was found in the non-bleeder group. A receiver operating characteristic (ROC) analysis indicated that the level of GPIbα shedding had a predictive power of NSB in patients on CF-LVAD support. Conclusions: Platelet GPIbα ectodomain shedding which attenuates platelet reactivity is associated with NSB. Plasma GPIbα level may potentially be used to refine bleeding risk stratification in CF-LVAD patients. [Copyright &y& Elsevier]

Abstract: Background: Large animal models serve as a critical link in the translation of basic science to clinical practice. However, large animal models of myocardial infarction (MI), especially large size MI, have been associated with high mortality because of arrhythmia. The prophylactic effect of amiodarone and lidocaine were retrospectively reviewed in our ovine MI model. Materials and methods: A total of 114 Dorset hybrid sheep with 25%–30% MI were included in the present study. The sheep were prophylactically treated with amiodarone plus lidocaine before ligation of the four to six coronary artery branches supplying the apex of the heart (arrhythmia prevention [AP] group, n = 45) and with epinephrine (shock prevention [SP] group, n = 49), respectively. The sheep without prophylactic treatment (no prevention [NP] group, n = 20) were used as the control group. The incidence of arrhythmia requiring treatment, mortality due to arrhythmia, hemodynamics, and arterial blood gas values during surgery were analyzed in these three groups. Results: No significant difference was found in infarct size among the three groups. The incidence of arrhythmia requiring treatment was significantly decreased in the AP group compared with that in the NP or SP groups (4.4% for AP versus 35% for NP and 45% for SP groups; P < 0.05). The mortality due to lethal arrhythmia was 2.2% in the AP group, significantly lower than that in the NP group (15%) or SP group (18.4%). Other than the heart rate, no significant differences were found in the hemodynamic data between the AP and NP groups. Metabolic acidosis was not observed in any group, as indicated by the pH and lactate values. Conclusions: Prophylactic amiodarone plus lidocaine decreased the mortality due to lethal arrhythmia after acute MI in our sheep model without significant negative effects on the hemodynamics. However, epinephrine improved the hemodynamics but also increased the mortality due to lethal arrhythmia. Thus, prophylactic amiodarone plus lidocaine is recommended to improve the stability in a large MI animal model. [Copyright &y& Elsevier]

In vitro and in vivo experimentation of various synthetic polymer hydrogels was conducted to establish some of the integral material properties that influence hemostasis. In vitro swelling experiments suggested that positive electrostatic charge was a key determinant of the ability of a polymer hydrogel to absorb physiological fluids, e.g. human plasma and blood. In vitro testing using unadulterated sheep blood suggested positive electrostatic charge and crosslink density were key determinants of the ability of a material to induce or enhance clot formation. Hydrogel formulations composed of higher amounts of positive electrostatic charge and lower crosslink density were able to effectively induce and enhance clot formation in the presence of a coagulation cascade activator. In vivo experimentation confirmed that hydrogels containing higher electrostatic charge and low crosslink density are more effective at fostering the formation of a robust hemostatic plug to control blood loss. [ABSTRACT FROM AUTHOR]

Abstract: The serine/threonine kinase Pim-1 was recently identified as a cardiomyocyte survival regulator downstream of Akt. The present study aims to examine Pim-1 activity and its association with the post MI remodeling myocardium in a clinically relevant large animal model. Apical myocardial infarction of approximately 25% left ventricular mass was created in an ovine model. Regional post-infarction deformation of the left ventricle was monitored by sonomicrometry and quantified using areal remodeling strain (i.e., areal expansion). Myocardial tissues were harvested at 12weeks from the adjacent and remote regions of the infarct for analysis of Pim-1 mediated survival signaling proteins as well as apoptotic activity. The cDNA coding sequences of two ovine Pim-1 kinase isoforms, 44 and 33kDa, were identified. Both isoforms were detected in heart tissue and the overall Pim-1 expression was found to be tightly controlled at multiple molecular levels. Pim-1 as well as the Pim-1 mediated survival signaling proteins Bcl-2, Bcl-xL, and phospho-Bad (Ser112) were upregulated in the adjacent region at 12weeks post-infarction and their expression correlated positively with the degree of the remodeling, which was accompanied by significant upregulations of the PP2A/BAD mediated apoptotic signaling proteins. However these upregulations were imbalanced, such that p-BAD (Ser112)/BAD decreased in the adjacent region of the infarcted hearts. Apoptotic activity also increased with remodeling strain. Despite an observed intrinsic upregulation of survival proteins, the imbalanced activation of apoptotic pathways resulted in evident apoptosis in the adjacent region. Ultramini-abstract: Pim-1 mediated survival signaling in myocardial tissues from infarcted ovine hearts was studied. It was shown that the adjacent region of the infarct experienced higher remodeling strain and exhibited increased levels of Pim-1 and related anti-apoptotic proteins. Despite this elevation of survival activity, however, the imbalanced activation of PP2A/BAD mediated apoptotic pathway resulted in evident apoptosis in the adjacent region. [Copyright &y& Elsevier]

The purpose of this study was to assess the biocompatibility of a newly developed long-term wearable artificial pump-lung ( APL) in a clinically relevant ovine animal model. The wearable APL device was implanted in five sheep through left thoracotomy. The device was connected between the right atrium and pulmonary artery and evaluated for 30 days. Three sheep were used as the sham control. Platelet activation was assessed by measuring platelet surface P-selectin ( CD62 P) expression with flow cytometry and plasma soluble P-selectin with an enzyme-linked immunosorbent assay. Thrombotic deposition on the device components and hollow fiber membranes were analyzed with digital imaging and scanning electron microscopy. Surface P-selectin of the APL and sham groups changed significantly over the study period, but without significant differences between the two groups. Soluble P-selectin for the two groups peaked in the first 24 h after the surgery. Soluble P-selectin of the APL group remained slightly elevated over the study period compared to the presurgical baseline value and was slightly higher compared to that of the sham group. Plasma free hemoglobin remained in the normal ranges in all the animals. In spite of the surgery-related alteration in laboratory tests and elevation of platelet activation status, the APL devices in all the animals functioned normally (oxygen transfer and blood pumping) during the 30-day study period. The device flow path and membrane surface were free of gross thrombus. Electron microscopy images showed only scattered thrombi on the fibers (membrane surface and weft). In summary, the APL exhibited excellent biocompatibility. Two forms of platelet activation, surgery-related and device-induced, in the animals implanted with the wearable APL were observed. The limited device-induced platelet activation did not cause gross thrombosis and impair the long-term device performance. [ABSTRACT FROM AUTHOR]

Abstract: Background: The underlying molecular mechanisms of the remodeling after myocardial infarction (MI) remain unclear. The purpose of this study was to investigate the role of a survival pathway (PI3K/Akt) and an apoptosis pathway (calcineurin/BAD) in the remodeling after MI in a large animal model. Methods: Ten Dorset hybrid sheep underwent 25% MI in the left ventricle (LV, n=10). Five sheep were used as sham control. The regional strain was calculated from sonomicrometry. Apoptosis and the activation of the PI3K/Akt and calcineurin/BAD pathways were evaluated in the non-ischemic adjacent zone and the remote zone relative to infarct by immunoblotting, immunoprecipitation, and immunofluorescence staining. Results: Dilation and dysfunction of LV were present at 12weeks after MI. The regional strain in the adjacent zone was significantly higher than in the remote zone at 12weeks (36.6±4.0% vs 9.5±3.6%, p< 0.05). Apoptosis was more severe in the adjacent zone than in the remote zone. The PI3K/Akt and calcineurin/BAD pathways were activated in the adjacent zone. Dephosphorylation and translocation of BAD were evident in the adjacent zone. Regional correlation between the strain and the expression of calcineurin/BAD indicated that the activation was strain-related (R 2 =0.46, 0.48, 0.39 for calcineurin, BAD, mitochondrial BAD, respectively, p <0.05). Conclusions: The PI3K/Akt survival and calcineurin/BAD apoptotic pathways were concomitantly activated in the non-ischemic adjacent zone after MI. The calcineurin/BAD pathway is strain related and its imbalanced activation may be one of the causes of progressive remodeling after MI. [Copyright &y& Elsevier]

With the recent advances in computer technology, computational fluid dynamics ( CFDs) has become an important tool to design and improve blood-contacting artificial organs, and to study the device-induced blood damage. Commercial CFD software packages are readily available, and multiple CFD models are provided by CFD software developers. However, the best approach of using CFD effectively to characterize fluid flow and to predict blood damage in these medical devices remains debatable. This study aimed to compare these CFD models and provide useful information on the accuracy of each model in modeling blood flow in circulatory assist devices. The laminar and five turbulence models (Spalart-Allmaras, k-ε (k-epsilon), k-ω (k-omega), SST [Menter's Shear Stress Transport], and Reynolds Stress) were implemented to predict blood flow in a clinically used circulatory assist device, the Centri Mag centrifugal blood pump. In parallel, a transparent replica of the Centri Mag pump was constructed and selected views of the flow fields were measured with digital particle image velocimetry ( DPIV). CFD results were compared with the DPIV experimental results. Compared with the experiment, all the selected CFD models predicted the flow pattern fairly well except the area of the outlet. However, quantitatively, the laminar model results were the most deviated from the experimental data. On the other hand, k-ε renormalization group theory models and Reynolds Stress model are the most accurate. In conclusion, for the circulatory assist devices, turbulence models provide more accurate results than the laminar model. Among the selected turbulence models, k-ε and Reynolds Stress Method models are recommended. [ABSTRACT FROM AUTHOR]

BACKGROUND: The infant Jarvik 2000 heart is a very small, hermetically sealed, intracorporeal, axial-flow ventricular assist device (VAD) designed for circulatory support in neonates and infants. The anatomic fit, short-term biocompatibility and hemodynamic performance of the device were evaluated in a neonate piglet model. METHODS: The infant Jarvik 2000 heart with two different blade profiles (low- or high-flow blade design) was tested in 6 piglets (8.8±0.9 kg). Using a median sternotomy, the pump was placed in the left ventricle through the apex without cardiopulmonary bypass. An outflow graft was anastomosed to the ascending aorta. Hemodynamics and biocompatibility were studied for 6 hours. RESULTS: All 6 pumps were implanted without complication. Optimal anatomic positioning was found with the pump body inserted 2.4 cm into the left ventricle. Hemodynamics demonstrated stability throughout the 6-hour duration. The pump flow increased from 0.27 to 0.95 liter/min at increasing speeds from 18 to 31 krpm for the low-flow blade design, whereas the pump flow increased from 0.54 liter/min to 1.12 liters/min at increasing speeds from 16 krpm to 31 krpm for the high-flow blade design. At higher speeds, >80% of flow could be supplied by the device. Blood chemistry and final pathology demonstrated no acute organ injury or thrombosis for either blade design. CONCLUSIONS: The infant Jarvik 2000 heart is anatomically and biologically compatible with an short-term neonate piglet model. This in vivo study demonstrates the future feasibility of this device for clinical use. [ABSTRACT FROM AUTHOR]

Background: To provide long-term ambulatory cardiopulmonary and respiratory support for adult patients, a novel wearable artificial pump-lung device has been developed. The design features and in vitro and acute in vivo performance of this device are reported. Methods: This device features a uniquely designed hollow-fiber membrane bundle integrated with a magnetically levitated impeller that together form one ultracompact pump-lung device, which can be placed like current paracorporeal ventricular assist devices to allow ambulatory support. The device is 117 mm in length and 89 mm in diameter and has a priming volume of 115 ml. In vitro hydrodynamic, gas transfer and biocompatibility experiments were carried out in mock flow-loops using ovine blood. Acute in vivo characterization was conducted in an ovine model by surgically implanting the device between right atrium and pulmonary artery. Results: The in vitro results show that the device with a membrane surface area of 0.8 m2 was capable of pumping blood from 1 to 4 liters/min against a wide range of pressures and transferring oxygen at a rate of up to 180 ml/min at a blood flow of 3.5 liters/min. Standard hemolysis tests demonstrated low hemolysis at the targeted operating condition. The acute in vivo results also confirmed that the device can provide sufficient oxygen transfer with excellent biocompatibility. Conclusions: Based on in vitro and acute in vivo study findings, this highly integrated wearable pump-lung device can provide efficient respiratory support with good biocompatibility and it is ready for long-term evaluation. [Copyright &y& Elsevier]

To assist the development and application of blood-contacting medical devices, two novel flow-through Couette-type blood-shearing devices have been developed to study the quantitative relationship between blood damage indexes and flow-dependent parameters. One device is an axial flow-through Couette-type device supported by a pair of pin bearings adapted from the adult Jarvik 2000 blood pump. The other is a centrifugal flow-through Couette-type device supported with magnetic bearings adapted from the CentriMag blood pump. In both devices, a rotor spindle was used to replace the original impeller blades so that a small gap was created between the housing and the rotating spindle surface. Computational fluid dynamics simulations have shown that a uniform, high shear stress region can be generated inside the small gap while the shear stresses elsewhere are relatively low. The possibility of secondary blood damage caused by mechanical seals was eliminated due to the use of a magnetic rotor system. Blood flow through the gap was driven by an externally pressurized reservoir. By adjusting the rotational speed and blood flow rate, shear-induced hemolysis was quantified at a matrix of exposure time (0.039 to 1.48 s) and shear stress (50 to 320 Pa). All of the experiments were conducted at room temperature using heparinized ovine blood with a hematocrit value of 30%. The measured hemolysis levels were much lower than those published in the literature, and the overestimation of those earlier studies may be attributable to device-related secondary blood-damaging effects. A new set of coefficients for the power law model was derived from the regression of the experimental data. [ABSTRACT FROM AUTHOR]

Abstract: Progress in the field of prosthetic cardiovascular devices has significantly contributed to the rapid advancements in cardiac therapy during the last four decades. The concept of mechanical circulatory assistance was established with the first successful clinical use of heart–lung machines for cardiopulmonary bypass. Since then a variety of devices have been developed to replace or assist diseased components of the cardiovascular system. Ventricular assist devices (VADs) are basically mechanical pumps designed to augment or replace the function of one or more chambers of the failing heart. Computational Fluid Dynamics (CFD) is an attractive tool in the development process of VADs, allowing numerous different designs to be characterized for their functional performance virtually, for a wide range of operating conditions, without the physical device being fabricated. However, VADs operate in a flow regime which is traditionally difficult to simulate; the transitional region at the boundary of laminar and turbulent flow. Hence different methods have been used and the best approach is debatable. In addition to these fundamental fluid dynamic issues, blood consists of biological cells. Device-induced biological complications are a serious consequence of VAD use. The complications include blood damage (haemolysis, blood cell activation), thrombosis and emboli. Patients are required to take anticoagulation medication constantly which may cause bleeding. Despite many efforts blood damage models have still not been implemented satisfactorily into numerical analysis of VADs, which severely undermines the full potential of CFD. This paper reviews the current state of the art CFD for analysis of blood pumps, including a practical critical review of the studies to date, which should help device designers choose the most appropriate methods; a summary of blood damage models and the difficulties in implementing them into CFD; and current gaps in knowledge and areas for future work. [Copyright &y& Elsevier]

The Levitronix UltraMag blood pump is a next generation, magnetically suspended centrifugal pump and is designed to provide circulatory support for pediatric and adult patients. The aim of this study is to investigate the hemodynamic and hemolytic characteristics of this pump using the computational fluid dynamics (CFD) approach. The computational domain for CFD analysis was constructed from the three-dimensional geometry (3D) of the UltraMag blood pump and meshed into 3D tetrahedral/hybrid elements. The governing equations of fluid flow were computationally solved to obtain a blood flow through the blood pump. Further, hemolytic blood damage was calculated by solving a scalar transport equation where the scalar variable and the source term were obtained utilizing an empirical power-law correlation between the fluid dynamic variables and hemolysis. To obtain mesh independent flow solution, a comparative examination of vector fields, hydrodynamic performance, and hemolysis predictions were carried out. Different sizes of tetrahedral and tetrahedral/hexahedral mixed hybrid models were considered. The mesh independent solutions were obtained by a hybrid model. Laminar and SST κ-ω turbulence flow models were used for different operating conditions. In order to pinpoint the most significant hemolytic region, the flow field analysis was coupled to the hemolysis predictions. In summary, computational characterization of the device was satisfactorily carried out within the targeted operating conditions of the device, and it was observed that the UltraMag blood pump can be safely operated for its intended use to create a circulatory support for both pediatric and adult-sized patients. [ABSTRACT FROM AUTHOR]

Abstract: The aim of this work was to develop a modeling approach to solve the flow and oxygen transfer when the blood passes through the hollow-fiber membrane bundle. For this purpose, a “two-region” modeling approach was developed regarding the hollow-fiber and blood regions. The oxygen transfer in these regions was defined with separate diffusion processes. Two-dimensional single and multi-fiber geometries were created and flow solutions were obtained for a non-Newtonian fluid. The convection–diffusion–reaction equation was solved to produce the oxygen partial pressure distributions. As a benefit of coupling the interstitial flow field into the oxygen transfer through the hollow-fiber membrane bundle, the membrane resistance was taken into consideration. Thus, varying oxygen partial pressures were observed on the outer fiber surface, which is contrary to the common simplifying assumptions of negligible membrane resistance and uniform oxygen content on the fiber surface (traditional approach). It was illustrated that, the current approach can be utilized to predict the mass transfer efficiencies without overestimating as compared to the predictions obtained with the traditional approach. Utilization of the current approach was found to be beneficial for the geometries with lower packing density which allows significant variations on the fiber surfaces. For the geometries with dense packings, the above simplifying assumptions could be applicable. The model predictions were validated with the experimental measurements taken from a benchmark device. [ABSTRACT FROM AUTHOR]