Study of a bi-directional axial flow blood pump

Abstract

A common treatment for circulatory disorders is the application of rotary blood pumps to locally increase blood flow to required levels. Existing devices tend to support flow from inlet to outlet and in that direction only. This thesis presents a bi-directional pump that may enable ventricle assist devices (VAD) to support blood flow to the organs during systole, when rotating in one direction, and to increase coronary perfusion during diastole, when rotating in the other. For each flow direction blade profiles were designed and tested for performance. Both designs were merged to obtain a symmetric profile to provide flow support in both directions. This initial bi-directional design was optimised using computational fluid dynamics modelling. The model was set to accelerate to a maximum forward rotational speed of 8,000 rpm, change rotational direction after 300 ms and accelerate to 2,400 rpm whilst rotating backwards. Experimental testing was carried out to validate the computational results. In the forward direction, the pump was predicted to deliver 39 cm3 compared to 19 cm3 in the backward direction. Pressure heads reached maxima of 2.2 kPa in forward and 0.16 kPa in backward direction. Analysis of wall shear stress profiles at the blades’ surface showed that the maximum was 140 Pa lasting less than 300 ms in the forward direction, whilst in the backward direction this was approximately 23 Pa lasting for 700 ms. A design for the bi-directional blades is established and characterised computationally and experimentally. Analysis of the blade pressure profiles confirmed generation of pressure rise in both directions. The computational results for wall shear stress were predicted to be below the accepted limits of haemolysis. Recirculation zones were found at the outlet in the backward rotating direction. Future work may reduce those by using guide vanes at either side of the rotor.