Development of a numerical pump testing framework.

It has been shown that left ventricular assist devices (LVADs) increase the survival rate in end-stage heart failure patients. However, there is an ongoing demand for an increased quality of life, fewer adverse events, and more physiological devices. These challenges necessitate new approaches during the design process. In this study, computational fluid dynamics (CFD), lumped parameter (LP) modeling, mock circulatory loops (MCLs), and particle image velocimetry (PIV) are combined to develop a numerical Pump Testing Framework (nPTF) capable of analyzing local flow patterns and the systemic response of LVADs. The nPTF was created by connecting a CFD model of the aortic arch, including an LVAD outflow graft to an LP model of the circulatory system. Based on the same geometry, a three-dimensional silicone model was crafted using rapid prototyping and connected to an MCL. PIV studies of this setup were performed to validate the local flow fields (PIV) and the systemic response (MCL) of the nPTF. After validation, different outflow graft positions were compared using the nPTF. Both the numerical and the experimental setup were able to generate physiological responses by adjusting resistances and systemic compliance, with mean aortic pressures of 72.2-132.6 mm Hg for rotational speeds of 2200-3050 rpm. During LVAD support, an average flow to the distal branches (cerebral and subclavian) of 24% was found in the experiments and the nPTF. The flow fields from PIV and CFD were in good agreement. Numerical and experimental tools were combined to develop and validate the nPTF, which can be used to analyze local flow fields and the systemic response of LVADs during the design process. This allows analysis of physiological control parameters at early development stages and may, therefore, help to improve patient outcomes.

Numerical washout study of a pulsatile total artificial heart.

PURPOSE: For blood pumps with long term indication, blood stagnation can result in excessive thromboembolic risks for patients. This study numerically investigates the washout performance of the left pump chamber of a pulsatile total artificial heart (TAH) as well as the sensitivity of the rotational orientation of the inlet bileaflet mechanical heart valve (MHV) on blood stagnation. METHODS: To quantitatively evaluate the washout efficiency, a fluid-structure interaction (FSI) simulation of the artificial heart pumping process was combined with a blood washout model. Four geometries with different orientations (0°, 45°, 90° and 135°) of the inlet valve were compared with respect to washout performance. RESULTS: The calculated flow field showed a high level of agreement with particle image velocimetry (PIV) measurements. Almost complete washout was achievable after three ejection phases. Remains of old blood in relation to the chamber volume was below 0.6% for all configurations and were mainly detected opposite to the inlet and outlet port at the square edge where the membrane and the pump chamber are connected. Only a small variation in the washout efficiency and the general flow field was observed. An orientation of 0° showed minor advantages with respect to blood stagnation and recirculation. CONCLUSIONS: Bileaflet MHVs were demonstrated to be only slightly sensitive to rotation regarding the washout performance of the TAH. The proposed numerical washout model proved to be an adequate tool to quantitatively compare different configurations and designs of the artificial organ regarding the potential for blood stagnation where experimental measurements are limited.

Combined computational and experimental approach to improve the assessment of mitral regurgitation by echocardiography.

Mitral regurgitation (MR) is one of the most frequent valvular heart diseases. To assess MR severity, color Doppler imaging (CDI) is the clinical standard. However, inadequate reliability, poor reproducibility and heavy user-dependence are known limitations. A novel approach combining computational and experimental methods is currently under development aiming to improve the quantification. A flow chamber for a circulatory flow loop was developed. Three different orifices were used to mimic variations of MR. The flow field was recorded simultaneously by a 2D Doppler ultrasound transducer and Particle Image Velocimetry (PIV). Computational Fluid Dynamics (CFD) simulations were conducted using the same geometry and boundary conditions. The resulting computed velocity field was used to simulate synthetic Doppler signals. Comparison between PIV and CFD shows a high level of agreement. The simulated CDI exhibits the same characteristics as the recorded color Doppler images. The feasibility of the proposed combination of experimental and computational methods for the investigation of MR is shown and the numerical methods are successfully validated against the experiments. Furthermore, it is discussed how the approach can be used in the long run as a platform to improve the assessment of MR quantification.