Regurgitation of a Mini Axial Pump with Closed Impeller Used As a Valvo-Pump

The back-flow of an aortic valvo-pump will reduce the pumping flow rate but can wash out the gap between the rotor and the stator, and thus can improve the antithrombogenicity of the device. To investigate the regurgitation of a 23 mm OD aortic valvo-pump, its closed impeller was replaced by a cylinder and hereby the valvo-pump had lost its pumping function. The pressure head crossing the aortic valvo- pump was maintained by a pulsatile centrifugal pump, beating rhythmically from 0 to 120 mmHg. The back flow from outlet to inlet of valvo-pump via the above-mentioned gap was measured. Results demonstrated that this gap and the pressure head had remarkable effect on back-flow; a larger gap and/or a larger pressure head would lead to a larger back-flow. By 0,20 mm gap and 100 mmHg pressure head, the valvo-pump had ca. 0,8 1/min back-flow. Instantaneous measurement indicated that the back-flow had a pulsatile form with high rate during diastole while low rate during systole of the natural heart imitated by pulsatile centrifugal pump. The pump rotated at 12500 rpm, 15000 rpm and 17500 rpm respectively, but it was found the rotating speed had no affection on back-flow. This investigation provides a basis for pump design seeking for both increase of the flow rate and improvement of the compatibility; the former is particularly important for a mini pump and the latter is extremely difficult for closed impeller.