Mechanical circulatory support (MCS) devices continue to be hampered by thrombotic adverse events (AEs), a consequence of device-imparted supraphysiologic shear stresses, leading to shear-mediated platelet activation (SMPA). In advancing MCS devices from design to clinical use, in vitro circulatory loops containing the device under development and testing are utilized as a means of assessing device thrombogenicity. Physical characteristics of these test circulatory loops may also contribute to inadvertent platelet activation through imparted shear stress, adding inadvertent error in evaluating MCS device thrombogenicity. While investigators normally control for the effect of a loop, inadvertent addition of what are considered innocuous connectors may impact test results. Here, we tested the effect of common, additive components of in vitro circulatory test loops, that is, connectors and loop geometry, as to their additive contribution to shear stress via both in silico and in vitro models. A series of test circulatory loops containing a ventricular assist device (VAD) with differing constituent components, were established in silico including: loops with 0~5 Luer connectors, a loop with a T-connector creating 90° angulation, and a loop with 90° angulation. Computational fluid dynamics (CFD) simulations were performed using a k − shear stress transport turbulence model to platelet activation index (PAI) based on a power law model. VAD-operated loops replicating in silico designs were assembled in vitro and gel-filtered human platelets were recirculated within (1 hour) and SMPA was determined. CFD simulations demonstrated high shear being introduced at non-smooth regions such as edge-connector boundaries, tubing, and at Luer holes. Noticeable peaks' shifts of scalar shear stress (sss) distributions toward high shear-region existed with increasing loop complexity. Platelet activation also increased with increasing shear exposure time, being statistically higher when platelets were exposed to connector-employed loop designs.The extent of platelet activation in vitro could be successfully predicted by CFD simulations. Loops employing additional components (non-physiological flow pattern connectors) resulted in higher PAI. Loops with more components (5-connector loop and 90° T-connector) showed 63% and 128% higher platelet activation levels, respectively, versus those with fewer (0-connector (P = .023) and a 90° heat-bend
The ideal variable displacement pump for a displacement control circuit is efficient across a wide operating range and readily mounted on a common shaft with multiple pumps. This paper presents a novel variable displacement pump architecture for displacement control circuits that uses the concept of alternating flow (AF) between piston pairs that share a common cylinder. The displacement is adjusted by varying the phase angle between the piston pairs. When the pistons are in phase, the pump displacement is at a maximum and when the pairs of pistons are out of phase, fluid is shuttled between the pistons and the pump produces no net flow. A prototype of the AF pump was constructed from two inline triplex pumps that were modified so that three piston pairs were created. The crankshafts of the two pumps were connected via a sprocket-and-chain transmission. The sprockets allow for accurate measurement of the phase angle, which is adjusted, in this early phase prototype, by disassembling the chain and shifting the sprockets. The prototype AF pump was then mounted to the test stand and experiments were conducted to map the AF pump efficiency and cylinder pressure dynamics across a range of operating pressure, speed, and displacement. The AF pump’s efficiency was measured for 8 diferent phase angles with an efficiency of near 90% at full flow and 65% at 36% displacement. The experimental results were compared to simulation results, presented in a companion paper at this conference.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.