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Effect of stationary guiding vanes on improvement of the washout behind the rotor in centrifugal blood pumps.

In centrifugal pumps, there always exists an area of stagnation between the rear of the rotor and the rear housing wall that promotes thrombus formation around the axle. Some current devices overcome the problem by using holes in the rotor plane, leading to increased hydrodynamic losses and shear stress. In this study, a simple apparatus was developed to overcome this problem. Guiding vanes were fixed to the rear housing wall. These vanes decrease the tangential velocity of the fluid and thus the centrifugal force, leading to an increased secondary flow toward the axle. The effect of such vanes was studied in videographic and ultrasound studies. An increase of washout and mixing between the flow layers could be demonstrated (stay time < 200 msec versus several seconds without vanes). In the first animal experiment using nonoptimized vanes, there was no thrombus at the back plane or the seal, and only a small thrombus at the transition between axle and rotor. Hemolysis was slightly elevated (3.2 mg/dl versus 2.5 mg/dl in control experiments). In conclusion, it is highly likely that this simple system will improve the flow characteristics in centrifugal pumps.