A Human Paired Sample Mock Loop for In Vitro Blood Pump Testing

Objectives: In vitro test settings for blood pumps are often designed to optimize technical parts (flow, pressure, resistance, shear stress), or to monitor biological/medical data (inflammation, coagulation, hemolysis), and use animal blood. Here we present a twin-Mock Loop which enables the paired analysis of blood from one human donor in two identical setups to investigate different hypotheses (e.g., substance A vs. B). The extracorporeal test setting simulates clinically relevant and physiological hematocrit, temperature, flow and pressure values.

Methods: The twin-Mock Loop consists of standard PVC tubing, a silicon reservoir, flow sensors, pressure transducers, temperature probes and a MEDOS sPump drive unit for each circuit. 100 mL of heparinized (HEP) human blood from healthy volunteers (37.5 IU/mL), is diluted to a HCT value of 20 to 25% with isotonic saline, to achieve a total volume of approximately 70 mL per circuit. This is sufficient for the withdrawal of six adequate blood samples from each loop to investigate changes in coagulation and platelet activation, blood gases, cell count, microvesicles, as well as cytokine expression and finally clot formation and hemolysis within the system during six hours. To evaluate the setting we compared three groups: 1st: HEP w/o antagonization (ANT), 2nd: 50% ANT of HEP with protamine, 3rd: 100% ANT of HEP with protamine.

Results: We simulated a “cardiac output” of 70 to 100 mL/min with a physiological mean pressure of 85.1 ± 1.2 mm Hg. Both parameters remained stable for the complete test cycle of 6 hours, independent from the experimental group. We achieved clot formation on the sPump with an average clot weight of 596mg within the 3rd group, decreased clotting time for the extrinsic (61 ± 2.6 to 48.6 ± 3.8 seconds) and intrinsic (>3,600 to 450 ± 101.7 seconds) coagulation measurement using ROTEM technology, as well as a 3-fold increased amount of CD62P positive platelets using FACS analysis. Free hemoglobin concentration, as sign for hemolysis, increased over time (14.7 ± 1.1 to 53 ± 4.6 mg/dL). In contrast, no clot formation was found in the other groups and only moderate changes for the mentioned parameters.

Conclusion: Our human Mock Loop system features near-physiological conditions in a novel paired sample setting, allowing direct within-patient comparison. It is suitable for the investigation of new anticoagulatory strategies and testing of diverse blood pumps toward susceptibility for clot formation and hemolysis.