Implantable left ventricular assist devices (LVADs) became the therapy of choice in treating end-stage heart failure. Although survival improved substantially and is similar in currently clinically implanted LVADs HeartMate II (HM II) and HeartWare HVAD, complications related to blood trauma are frequently observed. The aim of this study was to compare these two pumps regarding their potential blood trauma employing computational fluid dynamics. High-resolution structured grids were generated for the pumps. Newtonian flow was calculated, solving Reynolds-averaged Navier-Stokes equations with a sliding mesh approach and a k-ω shear stress transport turbulence model for the operating point of 4.5 L/min and 80 mm Hg. The pumps were compared in terms of volumes subjected to certain viscous shear stress thresholds, below which no trauma was assumed (von Willebrand factor cleavage: 9 Pa, platelet activation: 50 Pa, and hemolysis: 150 Pa), and associated residence times. Additionally, a hemolysis index was calculated based on a Eulerian transport approach. Twenty-two percent of larger volumes above 9 Pa were observed in the HVAD; above 50 Pa and 150 Pa the differences between the two pumps were marginal. Residence times were higher in the HVAD for all thresholds. The hemolysis index was almost equal for the HM II and HVAD. Besides the gap regions in both pumps, the inlet regions of the rotor and diffuser blades have a high hemolysis production in the HM II, whereas in the HVAD, the volute tongue is an additional site for hemolysis production. Thus, in this study, the comparison of the HM II and the HVAD using numerical methods indicated an overall similar tendency to blood trauma in both pumps. However, influences of turbulent shear stresses were not considered and effects of the pivot bearing in the HM II were not taken into account. Further in vitro investigations are required.

The aim of this study was to determine a method for the numerical estimation of blood damage. Normally, human or animal blood is used for in vitro evaluation of lysis by artificial organs. However, blood has some disadvantages: large biological variability and different initial test conditions lead to nonreproducible test results. For that reason, it would be an advantage to have a numerical method for blood damage estimation. This proposed method is based on the calculation of an integrated hemolysis and platelet lysis index along the path line in the flow field of the artificial organ. The time-dependent shear stress related lysis is based on known experimental data. In order to calibrate these data, the method was first applied to blood circulation in the human body. The results showed that the known data overestimate hemolysis by a factor of approximately 25. Next, the method was applied to a standard Björk-Shiley valve. The flow through a valve was simulated with the computational fluid dynamics program FLUENT. The calculation of lysis was added into FLUENT and done automatically. The results showed that the Björk-Shiley valve increased the hemolysis index by 7% if implanted in the human body circulation.

The surface roughness of left ventricular assist devices (LVADs) is important for the biocompatibility of blood pumps. However, little is known about the effect of surface roughness on the antithrombogenicity of the device. The present study investigated the effect of surface roughness on the activation of the coagulation system and platelet adhesion in an impeller-type blood pump. Three identical Baylor Gyro 710 centrifugal blood pumps (Baylor College of Medicine, Houston, TX, USA) were manufactured with impeller surface roughness of 0.05, 0.2, and 0.4 microm, respectively, as determined by a stylus profilometer and by scanning electron microscopy. Whole blood was anticoagulated (1-IU heparin/mL, ACT 250 s) and circulated for 60 min in an artificial circulatory system, simulating LVAD perfusion (5-L/min flow against 100 mm Hg). Enzyme-linked immunosorbent assays were developed to quantify fibrinogen- and von Willebrand factor (vWf) adsorption as well as platelet adhesion directly on the impellers of the pumps. Levels of prothrombin fragment F1.2 and thrombin-antithrombin (TAT) complex were measured in order to quantify activation of coagulation. Compared with the 0.05-microm surface, platelet adhesion was 40 and 76% higher on the 0.2- and 0.4-microm surface, respectively (P < 0.01). The evaluation of adsorbed fibrinogen and vWf showed significant higher protein antigen levels on the rougher surfaces (P < 0.01). Furthermore, nonpulsatile perfusion activated the coagulation system. By contrast, the surface roughness had no significant influence on plasma prothrombin F1.2 fragment- and TAT concentrations. Antithrombogenicity was significantly reduced in pumps with inferior metal-finishing quality.

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Abstract-A study was conducted to measure in vitro the procoagulant properties of platelets induced by flow through Carbomedics bileaflet and Bjork-Shiley monoleaflet mechanical heart valves (MHVs). Valves were mounted in a left ventricular assist device, and platelets were circulated through them under pulsatile flow. Platelet activation states (PAS) were measured during circulation using a modified prothrombinase method. Computational fluid dynamics (CFD) simulations of turbulent, transient, and nonNewtonian blood flow patterns generated by the two valve designs were done using the Wilcox k − ω turbulence model, and platelet shear-stress histories (the integral of shear-stress exposure with respect to time) through the two MHVs were calculated. PAS measurements indicated that the bileaflet MHV activated platelets at a rate more than twice that observed with the monoleaflet MHV. Turbulent flow patterns were evident in CFD simulations for both valves, and corroborated the PAS observations, showing that, for particles close to the leaflet(s), shear-stress exposure in the bileaflet MHV can be more than four times that in the monoleaflet valve.

The interaction of flow and thrombus generation often is a crucial question for the engineer working in the field of artificial organs. However, this interaction is only incompletely known, and quantitative data under well-defined experimental conditions are especially rare. These can be attained with the stagnation point flow chamber. This flow model applies platelet-rich plasma (PRP) as fluid. Its flow conditions are assessed with the help of computational fluid mechanics. In addition, the concept of the boundary layer is introduced, which permits assessment of the platelet flow along the wall. The results of the experiment indicate that platelets are deposited at a defined shear rate.

Hence, blood trauma might be reduced with this design. Based on these encouraging results, future in vitro investigations to investigate actual blood damage are intended.