Computational Design and Experimental Testing of a Novel Axial Flow LVAD

Abstract

Thousands of cardiac failure patients per year in the United States could benefit from long-term mechanical circulatory support as destination therapy. To provide an improvement over currently available devices, we have designed a fully implantable axial-flow ventricular assist device with a magnetically levitated impeller (LEV-VAD). In contrast to currently available devices, the LEV-VAD has an unobstructed blood flow path and no secondary flow regions, generating substantially less retrograde and stagnant flow. The pump design included the extensive use of conventional pump design equations and computational fluid dynamics (CFD) modeling for predicting pressure-flow curves, hydraulic efficiencies, scalar fluid stress levels, exposure times to such stress, and axial fluid forces exerted on the impeller for the suspension design. Flow performance testing was completed on a plastic prototype of the LEV-VAD for comparison with the CFD predictions. Animal fit trials were completed to determine optimum pump location and cannulae configuration for future acute and long-term animal implantations, providing additional insight into the LEV-VAD configuration and implantability. Per the CFD results, the LEV-VAD produces 6 l/min and 100 mm Hg at a rotational speed of approximately 6300 rpm for steady flow conditions. The pressure-flow performance predictions demonstrated the VAD's ability to deliver adequate flow over physiologic pressures for reasonable rotational speeds with best efficiency points ranging from 25% to 30%. The CFD numerical estimations generally agree within 10% of the experimental measurements over the entire range of rotational speeds tested. Animal fit trials revealed that the LEV-VAD's size and configuration were adequate, requiring no alterations to cannulae configurations for future animal testing. These acceptable performance results for LEV-VAD design support proceeding with manufacturing of a prototype for extensive mock loop and initial acute animal testing.

The use of computational fluid dynamics in the development of ventricular assist devices

“…The implementations of these CFD packages are either based on the finite volume23 method or finite element method. Fluent 36, 37, 38, 39, 40, 41 and CFX 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 11, 57, 58, 59, both available from ANSYS, Inc. (Canonsburg, PA) and STAR-CD from CD-Adapco 60, 61 (Melville, New York) are the CFD software packages used most often for analysis and modelling of blood flow in VADs. In addition, AcuSolve from ACUSIM Software 62 (Mountain View, CA) and Adina from Adina R&D (Watertown, MA) are also used.…”

“…The standard k-ε model has been used for computing the flow in several pumps including Xi’an Jiaotong University’s pump 40, Nanyang Technological University’s pump 41, the Virginia LEV-VAD 51, the Virginia PVAD (versions 1–4) 53, 11, 56, 55 and the Impella (2001) 59. Of these several investigations compared pressure rises with measurements: the largest error in the Virginia LEV-VAD was around 10 mmHg (10 % over) 51, in the PVAD2 the largest error was around 15 mmHg (13 % under) 11 and in the Impella (2001) the error was up to 24 mmHg (30 % under).…”

Numerical Design and Experimental Hydraulic Testing of an Axial Flow Ventricular Assist Device for Infants and Children

“…The k-turbulence model has been used for several years in designing our adult VAD prototypes and numerous other geometrically similar blood pumps with experimental validation. 18 The CFD analysis of the PVAD3 applied multiple turbulence models (k-, k-, and shear stress transport) in this overall design effort; this manuscript presents a comparison between the CFD k-model results and experimental data, presenting the most relevant results. Thus, we selected the k-turbulence model coupled with a log-log wall function to characterize near-wall flow conditions.…”

“…9,10 Blood behaves as a Newtonian fluid for conditions of high shear stresses (Ͼ0.7 Pa) and shear rates above 100 s Ϫ1 . 9,10,14,18 The shear stresses dominating the flow paths in this computational model are large enough that the assumption of Newtonian fluid properties is acceptable. In addition, the blood analog fluid that is used in the experimental testing of the prototype is Newtonian with comparable fluid properties.…”

Effects of Cone-Shaped Bend Inlet Cannulas of an Axial Blood Pump on Thrombus Formation: An Experiment and Simulation Study

“…Computational fluid dynamics (CFD) technology has been successfully used to design blood pumps and analyze their blood flow [16,17]. Particle image velocimetry (PIV) can test transient flow velocity indirectly by testing the flow displacement of the tracer particle in a brief time period.…”