INVESTIGATION OF THE FLOW NEAR THE WALL IN A PULSATILE BLOODPUMP

Abstract

The proper function of an artificial organ in the cardiovascular system depends very much on the blood flow adjacent to the artificial walls. These walls usually are made of artificial material and are thrombogenic to a lesser or larger degree. A blood flow with no flow separations and stagnation zones is required to avoid the generation of thrombi. A precondition for solving this problem is the assessment of the wall shear rate. Two methods to investigate the flow close to the wall were applied. The first method permits to look selectively at the flow close to the wall. It is based on the observation of light reflecting particles, which are suspended in the fluid. This method can he considered as being a special development of the particle image velocimetry (PIV). Instead of having a light sheet illuminating a cross section in the center of the flow, we only illuminate the particles near to the wall. Using a fluid, which permits the light to penetrate only the fluid close to the wall, makes this selection. The recorded images are processed using the cross-correlation method. A vector field of the wall shear flow is the result. The second method is the conventional particle image velocimetry in a central light plane. The combination of the different vector fields both methods permits a complete assessment of the flow inside the bloodpump. The results of the flow experiments in blood pumps show the viability of these methods. The direction of the flow at the wall can he assessed, as well as the stagnation lines and flow separation zones. It is possible to obtain the wall shear rate and to evaluate the risk of a thrombus generation.