Numerical hemolysis performance evaluation of a rotary blood pump under different speed modulation profiles

Characteristics and hemolysis analysis of centrifugal blood pumps under different speed modulations

Introduction

Constant-speed methods are widely applied and studied in rotary blood pumps. However, various speed modulation which have been used in commercial blood pump lacks validation of the ventricular assist capability and hemolysis potential.

Methods

This study investigates the hydrodynamic performance and hemolysis of a rotary ventricular assist device under sinusoidal speed modulation, focusing on the combined effects of phase, baseline speed, and speed fluctuation amplitude.

Results

Computational fluid dynamics (CFD) coupled with a dynamic cardiovascular model revealed that counter-phase modulation reduces hemolysis index (HI) fluctuations compared to in-phase conditions, while higher baseline speeds increase time-averaged HI due to prolonged exposure to non-physiological shear stress. Larger amplitudes expand the operational range but exacerbate HI variability.

Discussion

These findings demonstrate that phase synchronization critically balances pulsatility and hemocompatibility, providing actionable insights for adaptive speed control strategies in clinical practice.

Dynamic VAD simulations: Performing accurate simulations of ventricular assist devices in interaction with the cardiovascular system

Medical advancements, particularly in ventricular assist devices (VADs), have notably advanced heart failure (HF) treatment, improving patient outcomes. However, challenges such as adverse events (strokes, bleeding and thrombosis) persist. Computational fluid dynamics (CFD) simulations are instrumental in understanding VAD flow dynamics and the associated flow-induced adverse events resulting from non-physiological flow conditions in the VAD.This study aims to validate critical CFD simulation parameters for accurate VAD simulations interacting with the cardiovascular system, building upon the groundwork laid by Hahne et al. A bidirectional coupling technique was used to model dynamic (pulsatile) flow conditions of the VAD CFD interacting with the cardiovascular system. Mesh size, time steps and simulation method (URANS, LES) were systematically varied to evaluate their impact on the dynamic pump performance (dynamic H - Q curve) of the HeartMate 3, aiming to find the optimal simulation configuration for accurately reproduce the dynamic H - Q curve. The new Overlapping Ratio (OR) method was developed and applied to quantify dynamic H - Q curves.In particular, mesh and time step sizes were found to have the greatest influence on the calculated pump performance. Therefore, small time steps and large mesh sizes are recommended to obtain accurate dynamic H - Q curves. On the other hand, the influence of the simulation method was not significant in this study. This study contributes to advancing VAD simulations, ultimately enhancing clinical efficacy and patient outcomes.

Impact of Impeller Speed Adjustment Interval on Hemolysis Performance of an Intravascular Micro-Axial Blood Pump

BACKGROUND

In recent years, intravascular micro-axial blood pumps have been increasingly used in the treatment of patients with cardiogenic shock. The flow rate of such blood pumps requires adjustment based on the patient's physiological condition. Compared to a stable flow state with fixed rotation speed, adjusting the speed of blood pump impeller to alter flow rate may lead to additional hemolysis. This study aimed at elucidating the relationship between adjusting interval of a blood pump's impeller speed and the hemolysis index.

METHODS

By comparing simulation results with P-Q characteristic curves of the blood pump measured by experiments, the accuracy of the blood pump flow field simulation model was confirmed. In this study, a drainage tube was employed as the device analogous to an intravascular micro-axial blood pump for achieving similar shear stress levels and residence times. The hemolysis finite element prediction method based on a power-law model was validated through hemolysis testing of porcine blood flow through the drainage tube. The validated models were subsequently utilized to investigate the impact of impeller speed adjusting intervals on hemolysis in the blood pump.

RESULTS

Compared to steady flow, the results demonstrate that the hemolysis index increased to 6.3% when changing the blood pump flow rate from 2 L/min to 2.5 L/min by adjusting the impeller speed within 0.072 s.

CONCLUSIONS

An adjustment time of impeller speed longer than 0.072 s can avoid extra hemolysis when adjusting the intravascular micro-axial blood pump flow rate from 2 L/min to 2.5 L/min.

Optimizing the design of axial flow pump blades based on fluid characteristics

Non-physiological blood flow conditions in axial blood pumps lead to some complications, including hemolysis, platelet activation, thrombosis, and embolism. The high speed of the axial blood pump destroys large amounts of erythrocytes, thereby causing hemolysis and thrombosis. Thus, this study aims to reduce the vortices and reflux in the flow field by optimizing the axial blood pump. The axial blood pump and arterial flow field were modeled by the finite element method. The blood was assumed to be incompressible, turbulent, and Newtonian. The SST k-ω turbulence model was used. The frozen rotor method was also used to calculate the snapshot of motion. Many vortices and reflux exist in the flow field of the blood pump without optimization. The improved flow field had almost no vortex and reflux, thereby reducing the exposure time of blood. The optimized blood pump had little influence on the pressure field and shear stress field. The optimized blood pump mainly reduced the vortex, reflux, and the risk of thrombosis in the flow field. The flow field characteristics of an axial blood pump were studied, and the results showed the risk of thrombosis and hemolysis in the blood pump. In accordance with the relationship between the blade shape and the flow field, the blade of the blood pump was optimized, reducing the vortex and reflux of the flow field, as well as the risk of thrombosis.