BACKGROUND: The Food and Drug Administration (FDA) blood pump is an open-source benchmark cardiovascular device introduced for validating computational and experimental performance analysis tools. The time-resolved velocity field for the whole impeller has not been established, as is undertaken in this particle image velocimetry (PIV) study. The level of instantaneous velocity fluctuations is important, to assess the flow-induced rotor vibrations which may contribute to the total blood damage.
METHODS: To document these factors, time-resolved two-dimensional PIV experiments were performed that were precisely phase-locked with the impeller rotation angle. The velocity fields in the impeller and in the volute conformed with the previous single blade passage experiments of literature.
RESULTS: Depending on the impeller orientation, present experiments showed that volute outlet nozzle flow can fluctuate up to 34% during impeller rotation, with a maximum standard experimental uncertainty of 2.2%. Likewise, the flow fields in each impeller passage also altered in average 33.5%. Considerably different vortex patterns were observed for different blade passages, with the largest vortical structures reaching an average core radii of 7 mm. The constant volute area employed in the FDA pump design contributes to the observed velocity imbalance, as illustrated in our velocity measurements.
CONCLUSIONS: By introducing the impeller orientation parameter for the nozzle flow, this study considers the possible uncertainties influencing pump flow. Expanding the available literature data, analysis of inter-blade relative velocity fields is provided here for the first-time to the best of our knowledge. Consequently, our research fills a critical knowledge gap in the understanding of the flow dynamics of an important benchmark cardiovascular device. This study prompts the need for improved hydrodynamic designs and optimized devices to be used as benchmark test devices, to build more confidence and safety in future ventricular assist device performance assessment studies.

BACKGROUND: Blood clots are composed of aggregated fibrin and platelets, and thrombosis is the body\'s natural response to repairing injured blood vessels or stopping bleeding. However, when this process is activated abnormally, such as in a mechanical blood pump, it can lead to excessive thrombus formation. Therefore, how to avoid or reduce the probability of thrombus formation is an important indicator of the stable operation of a blood pump.
METHODS: In this paper, Lagrangian particle tracking trajectories are simulated to study platelet transport in a blood pump. The design of the thrombus blood pump was optimized using an orthogonal design method based on three factors: inlet angle, outlet angle, and blade number. The effect of blood pump pressure, rotational speed, impeller outlet angle, inlet angle, and number of blades on thrombus formation was analysed using Fluent software. The thrombogenic potential was derived by analyzing the trajectory and flow parameters of platelet particles in the blood pump, as well as the statistical parameters of residence time and stress accumulation thrombus in the platelet pump.
RESULTS: When the impeller inlet angle is 30°, the outlet angle is 20°, and the number of blades is 6, the probability of thrombus formation is minimized in the orthogonal design method, aligning with the requirements for blood pump performance.
CONCLUSIONS: These design parameters serve as a numerical guideline for optimizing the geometry of the semi-open impeller in blood pumps and provide a theoretical foundation for subsequent in vitro experiments.

Systematic research into device-induced red blood cell (RBC) damage beyond hemolysis, including correlations between hemolysis and RBC-derived extracellular vesicles, remains limited. This study investigated non-physiological shear stress-induced RBC damage and changes in related biochemical indicators under two blood pump clinical support conditions. Pressure heads of 100 and 350 mmHg, numerical simulation methods, and two in vitro loops were utilized to analyze the shear stress and changes in RBC morphology, hemolysis, biochemistry, metabolism, and oxidative stress. The blood pump created higher shear stress in the 350-mmHg condition than in the 100-mmHg condition. With prolonged blood pump operation, plasma-free hemoglobin and cholesterol increased, whereas plasma glucose and nitric oxide decreased in both loops. Notably, plasma iron and triglyceride concentrations increased only in the 350-mmHg condition. The RBC count and morphology, plasma lactic dehydrogenase, and oxidative stress across loops did not differ significantly. Plasma extracellular vesicles, including RBC-derived microparticles, increased significantly at 600 min in both loops. Hemolysis correlated with plasma triglyceride, cholesterol, glucose, and nitric oxide levels. Shear stress, but not oxidative stress, was the main cause of RBC damage. Hemolysis alone inadequately reflects overall blood pump-induced RBC damage, suggesting the need for additional biomarkers for comprehensive assessments.

Centrifugal blood pumps can be used for treating heart failure patients. However, pump thrombosis has remained one of the complications that trouble clinical treatment. This study analyzed the effect of impeller shroud on the thrombosis risk of the blood pump, and predicted areas prone to thrombosis. Multi-constituent transport equations were presented, considering mechanical activation and biochemical activation. It was found that activated platelets concentration can increase with shear stress and adenosine diphosphate(ADP) concentration increasing, and the highest risk of thrombosis inside the blood pump was under extracorporeal membrane oxygenation (ECMO) mode. Under the same condition, ADP concentration and thrombosis index of semi-shroud impeller can increase by 7.3% and 7.2% compared to the closed-shroud impeller. The main reason for the increase in thrombosis risk was owing to elevated scalar shear stress and more coagulation promoting factor-ADP released. The regions with higher thrombosis potential were in the center hole, top and bottom clearance. As a novelty, the findings revealed that impeller shroud can influence mechanical and biochemical activation factors. It is useful for identifying potential risk regions of thrombus formation based on relative comparisons.

Background: Hemolysis and its complications are major concerns during the clinical application of blood pumps. In-vitro circulatory testing loops have been employed as the key procedure to evaluate the hemolytic and thrombogenic performance of blood pumps during the development phase and before preclinical in-vivo animal studies. Except for the blood damage induced by the pump under test, blood damage induced by loop components such as the resistance valve may affect the accuracy, reproducibility, and intercomparability of test results. Methods: This study quantitatively investigated the impact of the resistance valve on in vitro evaluation of blood damage caused by blood pumps under different operating points. A series of idealized tubing models under the resistance valve with different openings were created. Three pumps - the FDA benchmark pump, the HeartMate 3 LVAD, and the CH-VAD - were involved in hypothetical tests. Eight operating points were chosen to cover a relatively wide spectrum of testing scenarios. Computational fluid dynamics (CFD) simulations of the tubing and pump models were conducted at the same operating points. Results and Conclusion: Overall, hemolysis and platelet activation induced by a typical resistance valve are equivalent to 17%-45% and 14%-60%, respectively, of those induced by the pump itself. Both ratios varied greatly with flow rate, valve opening and pump models. Differences in blood damage levels between different blood pumps or working conditions can be attenuated by up to 45%. Thus, hemolysis and platelet activation induced by the resistance valve significantly affect the accuracy of in-vitro hemocompatibility evaluations of blood pumps. A more accurate and credible method for hemocompatibility evaluations of blood pumps will benefit from these findings.

OBJECTIVE: Ventricular assist devices (VADs) are generally designed to perform continuous flow. However, it has been proven that continuous flow, which is not a physiological hemodynamic state, may cause severe complications such as gastrointestinal bleeding, pulmonary hypertension, and ventricular suction. For these reasons, many pulsating blood pump control strategies have been proposed and have the potential for application in percutaneous ventricular assist devices (pVADs) or microaxial blood pumps. A few cases report extra hemolysis when introducing pulsating speed, while none involve blood pumps. This research\'s primary purpose is to evaluate the potential hemolysis of pVAD under pulsating flow conditions.
METHODS: First, the pulsating flow state is deduced using a heart failure model and varying speed. The heart model is established according to the pathology state collected from a clinical check. The rotation speed and boundary physical state are set to fit the heart failure model. The computational fluid dynamics (CFD) method with the hemolysis prediction model is performed. Furthermore, we used proper orthogonal decomposition (POD) analysis to reconstruct the flow field and obtain more details about shearing and transporting effects.
RESULTS: (1) As a variable rotational speed was introduced, no significant gain in hemolysis accumulation appeared in pVAD. This is quite different from long-term implantable VADs. (2) Pulsation affects hemolysis mainly through pressure (or normal stress). Variable rotational speed affects hemolysis mainly through flow instability. (3) Variable rotational speed will increase the instability and influence hemolysis by transporting and shearing effects, while the transporting effect is more significant.
CONCLUSIONS: The unsteady flow state will affect the spatial distribution of hemolysis, which should be taken into account during control strategy and impeller shape design.

Extracorporeal centrifugal blood pumps are used to treat cardiogenic shock. Owing to the imbalanced excitation or initial assembly configurations, the variation in the impeller axial position has the potential to affect the blood pump performance. This study compared the hydrodynamics and hemolysis outcomes at different impeller axial positions via numerical simulations. The result shows that pressure difference of the blood pump decreased with increasing impeller axial position, with decreasing by 4.5% at a flow rate of 2 L/min. Under axial impeller motion close to the top pump casing, average wall shear stress and scalar shear stress reached their maximum values (64.2 and 29.1 Pa, respectively). The residence time in the impeller center hole and bottom clearance were extended to 0.5 s by increasing impeller axial position. Compared to the baseline blood pump, hemolysis index increased by 12.3% and 24.3% when impeller axial position is 2.5 and 4.0 mm, respectively. As a novelty, the findings reveal that the impeller axial position adversely affects hemolysis performance when the impeller is close to the pump casing. Therefore, in the development process of centrifugal blood pumps, the optimal axial position of the impeller must be defined to ensure hemodynamic performance.

BACKGROUND: Mechanical circulatory support (MCS), including ventricular assist devices (VADs), have emerged as promising therapeutic alternatives for end-stage congestive heart failure (CHF). The latest generation of these devices are continuous flow (CF) blood pumps. While there have been demonstrated benefits to patient outcomes due to CF-MCS, there continue to be significant clinical challenges. Research to-date has concentrated on mitigating thromboembolic risk (stroke), while the downstream impact of CF-MCS on the cerebrospinal fluid (CSF) flow has not been well investigated. Disturbances in the CSF pressure and flow patterns are known to be associated with neurologic impairment and diseased states. Thus, here we seek to develop an understanding of the pathophysiologic consequences of CF-MCS on CSF dynamics.
METHODS: We built and validated a computational framework using lumped parameter modeling of cardiovascular, cerebrovascular physics, CSF dynamics, and autoregulation. A sensitivity analysis was performed to confirm robustness of the modeling framework. Then, we characterized the impact of CF-MCS on the CSF and investigated cardiovascular conditions of healthy and end-stage heart failure.
RESULTS: Modeling results demonstrated appropriate hemodynamics and indicated that CSF pressure depends on blood flow pulsatility more than CSF flow. An acute equilibrium between CSF production and absorption was observed in the CF-MCS case, characterized by CSF pressure remaining elevated, and CSF flow rates remaining below healthy, but higher than CHF states.
CONCLUSIONS: This research has advanced our understanding of the impact of CF-MCS on CSF dynamics and cerebral hemodynamics.

Head-flow HQ curves for a Fontan cavopulmonary assist device (CPAD) were measured using a blood surrogate in a mock circulatory loop and simulated with various computational fluid dynamics (CFD) models. The tests benchmarked the CFD tools for further enhancement of the CPAD design. Recommended Reynolds-Averaged Navier-Stokes (RANS) CFD approaches for the development of conventional ventricular assist devices (VAD) were found to have shortcomings when applied to the Fontan CPAD, which is designed to neutralize off-condition obstruction risks that could contribute to a major adverse event. The no-obstruction condition is achieved with a von Karman pump, utilizing large clearances and small blade heights, which challenge conventional VAD RANS-based CFD hemodynamic simulations. High-fidelity large eddy simulation (LES) is always recommended; however, this may be cost-inhibitive for optimization studies in commercial settings, thus the reliance on RANS models. This study compares head and power predictions of various RANS turbulence models, employing experimental measurements and LES results as a basis for comparison. The models include standard k-ϵ, re-normalization group k-ϵ, realizable k-ϵ, shear stress transport (SST) k-ω, SST with transitional turbulence, and Generalized k-ω. For the pressure head predictions, it was observed that the standard k-ϵ model provided far better agreement with experiment. For the rotor torque, k-ϵ predictions were 30% lower than LES, while the SST and LES torque values were near identical. For the Fontan CPAD, the findings support using LES for the final design simulations, k-ϵ model for head and general flow simulation, and SST for power, shear stress, hemolysis, and thrombogenicity predictions.

Extracorporeal membrane oxygenation (ECMO) is a life support system used in the treatment of severe respiratory and circulatory failure. High shear stress caused by the high rotational speed of centrifugal blood pumps can cause hemolysis and platelet activation, which are among the major factors leading to the complications of the ECMO system. In this study, a novel blood pump named rotary displacement blood pump (RDBP), which can considerably reduce rotational speed and shear stress while ensuring the normal pressure flow relationship, was proposed. We employed computational fluid dynamics (CFD) analysis to investigate the performance of RDBP under adult ECMO support operating conditions (5 L/min with 350 mmHg). The efficiency and H-Q curves of the RDBP were calculated to evaluate its hydraulic performance, and pressure, flow patterns, and shear stress distribution were analyzed to estimate the hemodynamic characteristics in the pump. In addition, the modified index of hemolysis (MIH) was calculated for the RDBP based on a Eulerian approach. The hydraulic efficiency of the RDBP was 47.28%. The velocity distribution of flow field in the pump was relatively uniform. Most of the liquid (more than 75%) in the pump was exposed to low scale shear stress (<1 Pa), which was close to normal physiological conditions. The gap area was the main distribution location of high scale shear stress. The high wall shear stress (>9 Pa) volume fraction of the RDBP was small and located in the boundary areas between the rotor\'s edge and the housing. The MIH value of the RDBP was 9.87 ± 0.93 (mean ± SD). The RDBP can achieve better hydraulic efficiency and hemodynamic performance at lower rotational speed. The design of this novel pump is expected to provide a new direction for developing a blood pump for ECMO.