A control strategy for rotary blood pumps meeting different user-selectable control objectives is proposed: maximum support with the highest feasible flow rate versus medium support with maximum ventricular washout and controlled opening of the aortic valve (AoV). A pulsatility index (PI) is calculated from the pressure difference, which is deduced from the axial thrust measured by the magnetic bearing of the pump. The gradient of PI with respect to pump speed (GPI) is estimated via online system identification. The outer loop of a cascaded controller regulates GPI to a reference value satisfying the selected control objective. The inner loop controls the PI to a reference value set by the outer loop. Adverse pumping states such as suction and regurgitation can be detected on the basis of the GPI estimates and corrected by the controller. A lumped-parameter computer model of the assisted circulation was used to simulate variations of ventricular contractility, pulmonary venous pressure, and aortic pressure. The performance of the outer control loop was demonstrated by transitions between the two control modes. Fast reaction of the inner loop was tested by stepwise reduction of venous return. For maximum support, a low PI was maintained without inducing ventricular collapse. For maximum washout, the pump worked at a high PI in the transition region between the opening and the permanently closed AoV. The cascaded control of GPI and PI is able to meet different control objectives and is worth testing in vitro and in vivo.

No abstract

Cardiac surgery has made significant progress during the last 50 years. nowadays, almost every congenital or contracted dysfunction of the heart can be treated clinically or at least the etiopathology can be alleviated. During these years, implantable Left Ventricular Assist Devices (LVADs) have proven to be an effective and reliable medical product. In particular, the survival rate of patients with cardiac insufficiency has risen due to these devices. This type of heart‐assist device is implanted either to bridge the time until cardiac transplantation or recovery has occurred, or for permanent implantation in the patient's body.Berlin Heart GmbH produces the clinically tested axial pump system INCOR® (Figure 1, above). The INCOR heart‐as‐sisting pump is a powerful implantable LVAD which has been used in more than 500 clinical applications. The main function of the axial pump is to unload the patient's heart by transporting blood from the left ventricle to the aorta. In order to assure high reliability of the pump's operation, the components used for blood transport have to be highly bio‐ and hemocompatible.

Particle Image Velocimetry (PIV) analysis and Computational Fluid Dynamics (CFD) simulations have been performed on an innovative prototype of an implantable rotary axial pump. Numerically and experimentally estimated velocity and shear stress fields have been compared on several planes at different distances from the pump axis. An excellent agreement was generally observed in terms of mean flow velocity and viscous stresses, while the congruence of turbulent stresses was very good in some cases and less accurate in others. Further effort will be needed on both the numerical and the experimental side to better characterise near-wall flow features.