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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: 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]

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]