Single-Pass System to Characterize the Effects of Blood Species and Hematocrit on Flow-Induced Hemolysis

To assess hemolysis potential, blood pump developers frequently perform in vitro testing in accordance with the ASTM F1841 standard. However, options in test parameters such as blood species, anticoagulant, and blood collection and preparation methods can lead to inconsistent hemolysis results.

To improve in vitro hemolysis test sensitivity and characterize the impact of species and hematocrit (HCT) on flow-induced hemolysis, a pressure-driven, single-pass micro-nozzle test system with short blood exposure times was developed. To compare different blood species, porcine, bovine, ovine, and human blood pools were adjusted to 35% HCT, and 2.7 mL blood aliquots were pneumatically injected at different flow rates through two converging nozzle tips with diameters of 250 and 410 μm. Plasma-free hemoglobin (pfHb) concentration was measured to assess hemolysis after passing through the nozzle tip model. Additionally, porcine blood was tested at 25%, 35%, and 45% HCT using the 410 μm nozzle.

Using a single blood source, the repeatability for a single nozzle and reproducibility based on five separate nozzles were characterized. Results for the nozzles were consistent, with coefficients of variation of 0.5% for flow rate and less than 16% for pfHb levels. Hemolysis increased markedly with flow rate for all species, with pfHb levels being lowest for ovine and bovine blood and highest for human blood. Additionally, hemolysis increased non-linearly with increasing HCT.

The nozzle tip model can be used to examine other blood factors that impact hemolysis and to support and advance computational fluid dynamics hemolysis simulations.