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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]