Impact of adjustable resistance clamps on the in-vitro hemolysis assessment of blood pumps

Adjustable resistance clamps are essential to regulate flow and pressure in in-vitro test loops designed to evaluate hemolysis in blood pumps. However, their contribution to overall hemolysis remains unclear. This study investigated the hemolytic potential of adjustable resistance clamps across different resistance settings. Utilizing a single-pass test loop with heparinized bovine blood, the effect of resistance clamps on hemolysis was evaluated at three resistance settings: high (1.5 L/min, 90 mmHg), medium (5 L/min, 60 mmHg), and low (7.5 L/min, 30 mmHg). Two resistance clamps (sudden vs. gradual constriction) were compared at the medium resistance setting. Hemolysis was quantified by measuring plasma free hemoglobin (pfHb) and normalized index of hemolysis (NIH). Furthermore, computational fluid dynamics simulations were used to predict the hemolysis metric for each resistance setting with 3D-recreated replicas. Compared to hemolysis metrics reported for state-of-the-art blood pumps, resistance clamps may affect the hemolysis substantially, with up to 84% of the NIH at medium resistance settings and < 47% at low/high resistance settings, regardless of the resistance shape/profile. Numerically predicted hemolysis metric strongly correlated with experimental results for three resistance settings (r > 0.998). The findings underscore the importance of considering the influence of adjustable resistance clamps while investigating the hemolytic potential of blood pumps.