In Vitro Evaluation of the Dual‐Diffuser Design for a Reversible Rotary Intra‐Aortic Ventricular Assist Device

Abstract

The intra-aortic ventricular assist device (IntraVAD) is a miniature intra-aortic axial-flow ventricular assist device (VAD) that works in series with the left ventricle (LV) to assist the compromised heart. Previous in vitro results have shown that the IntraVAD can successfully increase coronary perfusion and offload ventricular volume by operating in reverse-rotation control (RRc) mode. The RRc mode includes forward rotation in systole and reverse rotation (RR) in diastole. It is necessary to derive a new diffuser design that can be used for the bi-directional rotation of the IntraVAD. In this work, a dual-diffuser set (DDS) was proposed to replace the conventional inducer and diffuser upstream and downstream of the pump. The DDS comprised two diffusers, located on both sides of the impeller, omitting the conventional inducer and diffuser. Different configurations of the DDS were designed and manufactured with various combinations of curved and straight blades. All configurations were initially tested in continuous flow, then in a pulsatile mock circulatory loop. A weighted normalized scalar (WNS) was proposed to comprehensively evaluate the hemodynamic effect of the DDS with different configurations. The results show that the maximum of WNS occurred when the upstream diffuser had equal numbers of curved and straight blades and the downstream diffuser had only curved blades. This indicates such a dual-diffuser design for the IntraVAD can give an optimal cardiac assistance potentially improving ventricular contractility, thereby restoring heart function.

Systematic Design of a Magnetically Levitated Brushless DC Motor for a Reversible Rotary Intra‐Aortic Blood Pump

“…An intra‐aortic ventricular assist device (IntraVAD) has been proposed that could be positioned in the aorta, thereby leaving the aortic valve and LV intact and working in series with the compromised LV to provide long‐term support . As illustrated schematically in Fig.…”

“…Passively levitated bearings require no sensors or electrical power, so they are a good choice for use in rotary blood pumps with stringent space limitations . However, in RRc mode, the IntraVAD periodically reverses rotational direction in synchrony with the cardiac cycle, leading to the changes in pressure force on the impeller . Because a passive axial bearing would not balance the magnetic and pressure forces when the impeller switches direction, it is necessary to design a magnetically levitated bearing for the IntraVAD that can periodically change its force direction and magnitude according to the rotational direction of the IntraVAD.…”

“…To determine the initial design values for the BLDC motor, thrust force due to the pressure difference over the pump, hydrodynamic torque and hydraulic efficiency were calculated from the results of our previous test on the mock circulatory loop (MCL) . In that test, the operational speed was set to 5000 rpm in FR during systole and 2500 rpm in RR during diastole, ensuring that compromised LV working with the IntraVAD can provide adequate cardiac output.…”

Development of rear‐impeller axial flow blood pump for realization of axial flow blood pump installed at aortic valve position

“…Wang et al developed a reversible axial VAD implanted at the ascending aorta, and the blood perfusion disturbance on the coronary flow was avoided by the synchronized forward/reverse rotation of the impeller with the cardiac cycle as an intra‐aortic balloon pump (IABP) counterpulsates with the left ventricle to increase coronary perfusion . However, it is difficult to design an upstream and downstream diffuser to maintain pump performance during reversible operation …”

“…9 However, it is difficult to design an upstream and downstream diffuser to maintain pump performance during reversible operation. 10 Letzen et al developed the intra-aortic axial VAD in which the impeller is placed at a rear position of the motor, and is coupled with the encapsulated motor by magnetic coupling force. However, friction in magnetic coupling causes energy loss and could cause hemolysis and thrombus formation.…”