Modeling and prediction of flow-induced hemolysis: a review

Hemolysis associated with Impella heart pump positioning: In vitro hemolysis testing and computational fluid dynamics modeling

INTRODUCTION

Short-term mechanical circulatory support devices provide temporary hemodynamic support in heart failure and are increasingly used to enable recovery or as a bridge to decision. Blood damage with mechanical circulatory support devices is influenced by many factors, including the magnitude and duration of shear stress and obstruction to blood flow. This study aimed to evaluate the effects of the Impella CP® heart pump positioning on hemolysis using in vitro hemolysis testing and computational fluid dynamics modeling.

METHODS

The in vitro hemolysis testing was conducted per the recommended Food and Drug Administration and American Society for Testing and Materials guidelines. The bench hemolysis testing and computational fluid dynamics simulation analysis were performed for both normal operating (outlet unobstructed) and outlet-obstructed condition of Impella CP (mimicking outlet on the aortic valve due to improper positioning).

RESULTS

The modified index of hemolysis was 2.78 ± 0.69 at normal operating conditions compared to 18.7 ± 7.8 when the Impella CP outlet was obstructed (p = 0.002). Computational fluid dynamics modeling showed about three times increase in exposure time to regions of high shear stress when the Impella CP outlet was obstructed compared to unobstructed condition, thus supporting the experimental observations.

CONCLUSION

Based on these results, it is recommended to ensure proper placement of Impella CP via regular monitoring using echocardiographic guidance or other methods to minimize the risk of hemolysis associated with an obstructed outflow.

Deformation of human red blood cells in extensional flow through a hyperbolic contraction

Flow-induced damage to red blood cells has been an issue of considerable importance since the introduction of the first cardiovascular devices. Early blood damage prediction models were based on measurements of damage by shear stress only. Subsequently, these models were extrapolated to include other components of the fluid stress tensor. However, the expanded models were not validated by measurements of damage in response to the added types of stress. Recent investigations have proposed that extensional stress might be more damaging to red cells than shear stress. In this study, experiments were conducted to compare human red cell deformation under laminar extensional stress versus laminar shear stress. It was found that the deformation caused by shear stress is matched by that produced by an extensional stress that is approximately 34 times smaller. Assuming that blood damage scales directly with cell deformation, this result indicates that mechanistic blood damage prediction models should weigh extensional stress more than shear stress.