Ventricular assist devices (VADs) provide long- and short-term support to chronically ill heart disease patients; these devices are expected to match the remarkable functionality of the natural heart, which makes their design a very challenging task. Blood pumps, the principal component of the VADs, must operate over a wide range of flow rates and pressure heads and minimise the damage to blood cells in the process. They should also be small to allow easy implantation in both children and adults. Mathematical methods and computational fluid dynamics (CFD) have recently emerged as powerful design tools in this context; a review of the recent advances in the field is presented here. This review focusses on the CFD-based design strategies applied to blood flow in blood pumps and other blood-handling devices. Both simulation methods for blood flow and blood damage models are reviewed. The literature is put into context with a discussion of the chronological development in the field. The review is illustrated with specific examples drawn from our group's Galerkin/least squares (GLS) finite-element simulations of the basic Newtonian flow problem for the continuous-flow centrifugal GYRO blood pump. The GLS formulation is outlined, and modifications to include models that better represent blood rheology are shown. Haemocompatibility analysis of the pump is reviewed in the context of haemolysis estimations based on different blood damage models. Our strain-based blood damage model that accounts for the viscoleasticity associated with the red blood cells is reviewed in detail. The viability of design improvement based on trial and error and complete simulation-based design optimisation schemes are also discussed.

Computational fluid dynamics (CFD) is increasingly being used to develop blood-contacting medical devices. However, the lack of standardized methods for validating CFD simulations and blood damage predictions limits its use in the safety evaluation of devices. Through a U.S. Food and Drug Administration (FDA) initiative, two benchmark models of typical device flow geometries (nozzle and centrifugal blood pump) were tested in multiple laboratories to provide experimental velocities, pressures, and hemolysis data to support CFD validation. In addition, computational simulations were performed by more than 20 independent groups to assess current CFD techniques. The primary goal of this article is to summarize the FDA initiative and to report recent findings from the benchmark blood pump model study. Discrepancies between CFD predicted velocities and those measured using particle image velocimetry most often occurred in regions of flow separation (e.g., downstream of the nozzle throat, and in the pump exit diffuser). For the six pump test conditions, 57% of the CFD predictions of pressure head were within one standard deviation of the mean measured values. Notably, only 37% of all CFD submissions contained hemolysis predictions. This project aided in the development of an FDA Guidance Document on factors to consider when reporting computational studies in medical device regulatory submissions. There is an accompanying podcast available for this article. Please visit the journal's Web site (www.asaiojournal.com) to listen.

In vitro cardiovascular device performance evaluation in a mock circulation loop (MCL) is a necessary step prior to in vivo testing. A MCL that accurately represents the physiology of the cardiovascular system accelerates the assessment of the device's ability to treat pathological conditions. To serve this purpose, a compact MCL measuring 600 × 600 × 600 mm (L × W × H) was constructed in conjunction with a computer mathematical simulation. This approach allowed the effective selection of physical loop characteristics, such as pneumatic drive parameters, to create pressure and flow, and pipe dimensions to replicate the resistance, compliance, and fluid inertia of the native cardiovascular system. The resulting five-element MCL reproduced the physiological hemodynamics of a healthy and failing heart by altering ventricle contractility, vascular resistance/compliance, heart rate, and vascular volume. The effects of interpatient anatomical variability, such as septal defects and valvular disease, were also assessed. Cardiovascular hemodynamic pressures (arterial, venous, atrial, ventricular), flows (systemic, bronchial, pulmonary), and volumes (ventricular, stroke) were analyzed in real time. The objective of this study is to describe the developmental stages of the compact MCL and demonstrate its value as a research tool for the accelerated development of cardiovascular devices.

Transcatheter aortic valve replacement (TAVR) represents an established recent technology in a high risk patient base. To better understand TAVR performance, a fluid-structure interaction (FSI) model of a self-expandable transcatheter aortic valve was proposed. After an in vitro durability experiment was done to test the valve, the FSI model was built to reproduce the experimental test. Lastly, the FSI model was used to simulate the virtual implant and performance in a patient-specific case. Results showed that the leaflet opening area during the cycle was similar to that of the in vitro test and the difference of the maximum leaflet opening between the two methodologies was of 0.42%. Furthermore, the FSI simulation quantified the pressure and velocity fields. The computed strain amplitudes in the stent frame showed that this distribution in the patient-specific case is highly affected by the aortic root anatomy, suggesting that the in vitro tests that follow standards might not be representative of the real behavior of the percutaneous valve. The patient-specific case also compared in vivo literature data on fast opening and closing characteristics of the aortic valve during systolic ejection. FSI simulations represent useful tools in determining design errors or optimization potentials before the fabrication of aortic valve prototypes and the performance of tests.

The complex fluid-structure interaction problem associated with the flow of blood through a heart valve with flexible leaflets is investigated both experimentally and numerically. In the experimental test rig, a pulse duplicator generates a pulsatile flow through a biomimetic rigid aortic root where a model of aortic valve with polymer flexible leaflets is implanted. High-speed recordings of the leaflets motion and particle image velocimetry measurements were performed together to investigate the valve kinematics and the dynamics of the flow. Large eddy simulations of the same configuration, based on a variant of the immersed boundary method, are also presented. A massively parallel unstructured finite-volume flow solver is coupled with a finite-element solid mechanics solver to predict the fluid-structure interaction between the unsteady flow and the valve. Detailed analysis of the dynamics of opening and closure of the valve are conducted, showing a good quantitative agreement between the experiment and the simulation regarding the global behavior, in spite of some differences regarding the individual dynamics of the valve leaflets. A multicycle analysis (over more than 20 cycles) enables to characterize the generation of turbulence downstream of the valve, showing similar flow features between the experiment and the simulation. The flow transitions to turbulence after peak systole, when the flow starts to decelerate. Fluctuations are observed in the wake of the valve, with maximum amplitude observed at the commissure side of the aorta. Overall, a very promising experiment-vs-simulation comparison is shown, demonstrating the potential of the numerical method.

Large skull defects as a result of craniectomies due to cerebral insults, trauma, or tumors create functional and aesthetic disturbances for the patient. Cranioplasty with implants in these cases are an alternative to autogenous bone transplantation. In our clinic, customized titanium or optima poly-ether-ether ketone (PEEK) implants are used to reconstruct craniectomy defects. To compare the two materials we investigated the structural changes of the implants fixed to a sintered polyamide skull model under mechanical stress in four simplified models. In a standard testing machine, the models were subjected to a load under a quasi-static loading rate of 1.925 mm/min. Fractures of the PEEK implants occurred at a force of 24.2 and 24.5 kN with a displacement of 8.4 and 8 mm. The titanium implants showed no deformation, but extensive damage was seen in the polyamide skull models. The highest pressures achieved were 45.8 and 50.9 kN. In a simplified model with quasi-static loading, both implants withstood forces that were higher than those capable of causing skull fractures. It seems that the mechanical properties of PEEK could provide better protection when used for cranioplasty in patients after craniectomy if reconstruction with autogenous bone is not possible.

Pre-existing RBBB and elevated LCC calcification were identified as independent predictors for PPI. These two risk factors enabled us to distinguish between patients according to their risk for PPI after TAVI. Ex vivo simulations suggested an off-centreline shift of the balloon as a possible explanation.

BackgroundExtracorporeal carbon dioxide removal (ECCO2R) uses an extracorporeal circuit to directly remove carbon dioxide from the blood either in lieu of mechanical ventilation or in combination with it. While the potential benefits of the technology are leading to increasing use, there are very real risks associated with it. Several studies demonstrated major bleeding and clotting complications, often associated with hemolysis and poorer outcomes in patients receiving ECCO2R. A better understanding of the risks originating specifically from the rotary blood pump component of the circuit is urgently needed.MethodsHigh-resolution computational fluid dynamics was used to calculate the hemodynamics and hemocompatibility of three current rotary blood pumps for various pump flow rates.ResultsThe hydraulic efficiency dramatically decreases to 5–10% if operating at blood flow rates below 1 L/min, the pump internal flow recirculation rate increases 6–12-fold in these flow ranges, and adverse effects are increased due to multiple exposures to high shear stress. The deleterious consequences include a steep increase in hemolysis and destruction of platelets.ConclusionsThe role of blood pumps in contributing to adverse effects at the lower blood flow rates used during ECCO2R is shown here to be significant. Current rotary blood pumps should be used with caution if operated at blood flow rates below 2 L/min, because of significant and high recirculation, shear stress, and hemolysis. There is a clear and urgent need to design dedicated blood pumps which are optimized for blood flow rates in the range of 0.5–1.5 L/min.