Hemolytic Performance in Two Generations of the Sputnik Left Ventricular Assist Device: A Combined Numerical and Experimental Study

Background: Currently, left ventricular assist devices (LVADs) are a successful surgical treatment for patients with end-stage heart failure on the waiting list or with contraindicated heart transplantation. In Russia, Sputnik 1 LVAD was also successfully introduced into clinical practice as a bridge-to-transplant and a destination therapy device. Development of Sputnik 2 LVAD was aimed at miniaturization to reduce invasiveness, optimize hemocompatibility, and improve versatility for patients of various sizes. Methods: We compared hemolysis level in flow path of the Sputnik LVADs and investigated design aspects influencing other types of blood damage, using predictions of computational fluid dynamics (CFD) and experimental assessment. The investigated operating point was a flow rate of 5 L/min and a pressure head of 100 mm Hg at an impeller rotational speed of 9100 min⁻¹. Results: Mean hemolysis indices predicted with CFD were 0.0090% in the Sputnik 1 and 0.0023% in the Sputnik 2. Averaged values of normalized index of hemolysis obtained experimentally for the Sputnik 1 and the Sputnik 2 were 0.011 ± 0.003 g/100 L and 0.004 ± 0.002 g/100 L, respectively. Conclusions: Obtained results indicate obvious improvements in hemocompatibility and sufficiently satisfy the determined miniaturization aim for the Sputnik 2 LVAD development.

Enhanced discrete phase model for multiphase flow simulation of blood flow with high shear stress

Shear stress is often present in the blood flow within blood-contacting devices, which is the leading cause of hemolysis. However, the simulation method for blood flow with shear stress is still not perfect, especially the multiphase flow model and experimental verification. In this regard, this study proposes an enhanced discrete phase model for multiphase flow simulation of blood flow with shear stress. This simulation is based on the discrete phase model (DPM). According to the multiphase flow characteristics of blood, a virtual mass force model and a pressure gradient influence model are added to the calculation of cell particle motion. In the experimental verification, nozzle models were designed to simulate the flow with shear stress, varying the degree of shear stress through different nozzle sizes. The microscopic flow was measured by the Particle Image Velocimetry (PIV) experimental method. The comparison of the turbulence models and the verification of the simulation accuracy were carried out based on the experimental results. The result demonstrates that the simulation effect of the SST k-ω model is better than other standard turbulence models. Accuracy analysis proves that the simulation results are accurate and can capture the movement of cell-level particles in the flow with shear stress. The results of the research are conducive to obtaining accurate and comprehensive analysis results in the equipment development phase.

MODIFICATION OF THE SPALART–ALLMARAS MODEL FOR HEMOLYTIC SHEAR FLOW SIMULATION WITH PIV EXPERIMENT

Hemolysis in blood-contacting devices severely affects the health of users, and computation fluid dynamics (CFD) simulation is a crucial method for hemolysis analysis. Medical equipment has high requirements for simulation accuracy. Modification of the turbulence model is one of the most effective ways to improve efficiency. In this study, we designed nozzle models to simulate hemolytic shear flow, varying the degree of shear flow through different nozzle orifice sizes. The study acquires microscopic flow results through Particle Image Velocimetry (PIV) experiments, and the Sparlart–Allmaras (S–A) model was modified based on the experimental results. In the study, we obtained the influence characteristics of the model coefficients on the simulation results and completed the accuracy correction. The results showed that the model coefficient [Formula: see text] has the most significant effect on the simulation results. Correcting [Formula: see text] to about 200% of the standard value can significantly improve the simulation accuracy, and the high shear flow intensity corresponds to a slightly lower correction value. The model modification eliminates the simulation error in the high-speed area, and the comparison results show that it is superior to the standard turbulence model.

Advances in Hemodynamic Analysis in Cardiovascular Diseases Investigation of Energetic Characteristics of Adult and Pediatric Sputnik Left Ventricular Assist Devices during Mock Circulation Support

The need to simulate the operating conditions of the human body is a key factor in every study and engineering process of a bioengineering device developed for implantation. In the present paper, we describe in detail the interaction between the left ventricle (LV) and our Sputnik left ventricular assist devices (LVADs). This research aims to evaluate the influence of different rotary blood pumps (RBPs) on the LV depending on the degree of heart failure (HF), in order to investigate energetic characteristics of the LV-LVAD interaction and to estimate main parameters of left ventricular unloading. We investigate energetic characteristics of adult Sputnik 1 and Sputnik 2 LVADs connected to a hybrid adult mock circulation (HAMC) and also for the Sputnik pediatric rotary blood pump (PRBP) connected to a pediatric mock circulation (PMC). A major improvement of the LV unloading is observed during all simulations for each particular heart failure state when connected to the LVAD, with sequential pump speed increased within 5000–10000 rpm for adult LVADs and 6000–13000 rpm for PRBP with 200 rpm step. Additionally, it was found that depending on the degree of heart failure, LVADs influence the LV in different ways and a significant support level cannot be achieved without the aortic valve closure. Furthermore, this study expands the information on LV-LVAD interaction, which leads to the optimization of the RBP speed rate control in clinics for adult and pediatric patients suffering from heart failure. Finally, we show that the implementation of control algorithms using the modulation of the RBP speed in order to open the aortic valve and unload the LV more efficiently is necessary and will be content of further research.

Optimisation of the Sputnik-VAD Design

Purpose

Miniaturisation of VADs can offer important benefits, including less invasive implantation techniques and more versatility in patient selection. The aim of this work was to reduce the weight, size, and energy consumption of the Sputnik VAD.

Methods

The second generation of the Sputnik VAD was developed with a set of changes in construction. The head pressure-flow rate (H-Q) and power consumption-flow rate curves for the Sputnik VADs were measured at different rotational speeds. Computational fluid dynamics (CFD) were used for operating condition simulation and the LVADs were compared under the simulated physiological conditions.

Results

The slope of the H-Q curves for the Sputnik 1 VAD remains almost invariable over the entire range of the measured flow rate, in contrast to the curves for the Sputnik 2 VAD, which become flat in the high flow-rate region. Despite the design modification, the operating rotor speed remained invariable. The preload sensitivity of the Sputnik VAD is higher than that of the other rotary blood pumps and amounts to 0.111 ± 0.0092 L min−1 mmHg−1. The power consumption for the Sputnik 2 VAD is lower over the entire speed range, except for at 5,000 rpm.

Conclusions

The pump weight was reduced from 246 to 205 g, the pump length was decreased from 82 to 66 mm, and the pump diameter was decreased from 32 to 29 mm. The total energy consumption of the pump was reduced by 15%.