Development and Validation of a Computational Fluid Dynamics Methodology for Simulation of Pulsatile Left Ventricular Assist Devices

Abstract

An unsteady computational fluid dynamic methodology was developed so that design analyses could be undertaken for devices such as the 50cc Penn State positive-displacement left ventricular assist device (LVAD). The piston motion observed in vitro was modeled, yielding the physiologic flow waveform observed during pulsatile experiments. Valve closure was modeled numerically by locally increasing fluid viscosity during the closed phase. Computational geometry contained Bjork-Shiley Monostrut mechanical heart valves in mitral and aortic positions. Cases for computational analysis included LVAD operation under steady-flow and pulsatile-flow conditions. Computations were validated by comparing simulation results with previously obtained in vitro particle image velocimetry (PIV) measurements. The steady portion of the analysis studied effects of mitral valve orientation, comparing the computational results with in vitro data obtained from mock circulatory loop experiments. The velocity field showed good qualitative agreement with the in vitro PIV data. The pulsatile flow simulations modeled the unsteady flow phenomena associated with a positive-displacement LVAD operating through several beat cycles. Flow velocity gradients allowed computation of the scalar wall strain rate, an important factor for determining hemodynamics of the device. Velocity magnitude contours compared well with PIV data throughout the cycle. Computational wall shear rates over the pulsatile cycle were found to be in the same range as wall shear rates observed in vitro.

The Influence of Different Operating Conditions on the Blood Damage of a Pulsatile Ventricular Assist Device

“…28 The valves were fixed in the fully opened phase. To model the valve closure phase, the fluid viscosity in the region local to the valves was increased by 1e+4, resulting in a velocity of approximating zero through the "closed" valve.…”

The Use of Fluid Mechanics to Predict Regions of Microscopic Thrombus Formation in Pulsatile VADs

“…In previous work, Medvitz et al simulated pulsatile flow through the V-2 VAD [17] at a flow rate of 3.8 lpm, 75 bpm and a constant LVAD pressure rise of 80 mm Hg for each cycle. Unlike the in vitro experiments, the fluid was considered to be Newtonian.…”

“…The V-2 model was characterized by a straight rear wall and ports equidistant from the midline of the pump and parallel to one another and was found to be the best design based on PIV studies [16]. Computational simulations add another dimension to fluid mechanics studies and offer support to observations made clinically and in vitro [17]. The VAD models previously discussed have been recreated computationally by Medvitz [17,18].…”

“…Computational simulations add another dimension to fluid mechanics studies and offer support to observations made clinically and in vitro [17]. The VAD models previously discussed have been recreated computationally by Medvitz [17,18]. …”

Computational Models of Aortic Coarctation in Hypoplastic Left Heart Syndrome: Considerations on Validation of a Detailed 3D model

“…However, it is crucial to demonstrate the reliability of the computational model by means of a suitable validation study. Validation is a process whereby results from the computational method are verified against those physically observed (10)(11)(12)(13); in vitro measurements can be a valuable source of validation data for this process. Once the model is thoroughly validated, the study can be taken forward in silico with confidence.…”