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Background: 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. Methods: 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. Results: 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. Conclusions: 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: 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: 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: 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]

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]