Minimization of Hemolysis in Centrifugal Blood Pumps: Influence of Different Geometries

Abstract

Centrifugal blood pumps are of substantial importance for intraoperative extracorporeal circulation and for temporary cardiac assist. Their development and improvement raises many specific questions, especially on mechanical blood properties, flow distribution, and the resulting biocompatibility. In this comprehensive study the influence of various pump geometries on blood trauma was investigated. For this purpose analytical calculations, hydrodynamic performance, numerical simulation, in vitro hemolysis tests and in vivo experiments were used. The gap between rotor and housing was found to be crucial showing a distinct minimum of hemolysis at a gap of 1.5 mm (in vitro increase of plasma free hemoglobin per 100 ml plasma an hour: delta fHb/hour = 2.4 +/- 0.83 mg%/h at 1.5 mm versus 12 +/- 2.2 mg%/h at 2.5 mm; p < 0.05). Housing diameter and shape of the vanes were of less importance for blood traumatization (d = 60 mm: delta fHb/hour = 6.36 +/- 1.8 mg%/h; d = 70 mm: fHb = 7.1 +/- 1.9 mg%/h; straight radial vanes: 5.2 +/- 1.8 mg%/h; straight inclined vanes: 6.8 +/- 1.2 mg%/h; flexed vanes: 6.1 +/- 2.0 mg%/h). Three animal experiments confirmed the optimization of geometry, with a mean fHb of 2.5 to 3.2 mg% in steady state. Hydrodynamic efficiency revealed to be a necessary, but not a sufficient and sensitive criterion for hemolysis minimization (e.g. changes of eta < 10% for changes of fHb > 500%). Numerical simulation gives an improved insight in flow distribution, but can not yet be applied for quantification of blood trauma.(ABSTRACT TRUNCATED AT 250 WORDS)

Hemolytic characteristics of three commercially available centrifugal blood pumps

“…Blood damage in centrifugal pumps is primarily caused by shear stress, time, and turbulent flow (22)(23)(24)(25). Circuit clotting has also been sited as a cause for elevated freeHb (4).…”

Towards Non-thrombogenic Performance of Blood Recirculating Devices

“…Flow-induced blood trauma was almost exclusively studied in respect to red blood cells (RBC) damage (hemolysis), and has become a standardized development tool 80,84,85. However, in recent years it was shown that platelet activation and thrombogenicity is the salient aspect of this blood trauma 86.…”

Study on the Development of Two-Stage Centrifugal Blood Pump for Cardiopulmonary Support System

“…In the study of Schima et al [4], the tip clearance of 1.5mm leads to the minimum amount of hemolysis in a single stage centrifugal pump with an impeller similar to the present pump impeller, although a shear velocity in the tip clearance around the periphery of the impeller in the reference [4] is low and about 27% (2300 s -1 ) of the shear velocity of 8400 s -1 in the present pump. In the studies of Miyazoe et al [5] and Masuzawa et al [6], the effect of the tip clearance was examined and it was found that the shear stress in the fluid and the amount of hemolysis significantly decrease by changing the tip clearance from 0.5 mm to 1 mm.…”

“…In the study of Schima et al [4], the amount of the hemolysis became smallest in the case with the tip clearance of 1.5 mm in a single stage centrifugal pump. Therefore, we conducted the computation for the pump with the tip clearance of 1.5 mm.…”