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research-article

Characterizing the HeartMate II Left Ventricular Assist Device Outflow Using Particle Image Velocimetry

[+] Author and Article Information
Grant/W Rowlands

Department of Biomedical Engineering, The Pennsylvania State University, 205 Hallowell Building, University Park, PA 16802, USA
gwr5056@gmail.com

Bryan Good

Department of Biomedical Engineering, The Pennsylvania State University, 205 Hallowell Building, University Park, PA 16802, USA
bcg5069@psu.edu

Steven Deutsch

Department of Biomedical Engineering, The Pennsylvania State University, 205 Hallowell Building, University Park, PA 16802, USA
sdeutsch22@gmail.com

Keefe B. Manning

Professor, Department of Biomedical Engineering, The Pennsylvania State University, 205 Hallowell Building, University Park, PA 16802, USA; Department of Surgery, Penn State Hershey Medical Center, Hershey, PA 17033, USA
kbm10@psu.edu

1Corresponding author.

ASME doi:10.1115/1.4039822 History: Received July 25, 2017; Revised March 25, 2018

Abstract

Ventricular assist devices (VADs) are implanted in patients with a diseased ventricle to maintain peripheral perfusion as a bridge-to-transplant or as destination therapy. However, some patients with continuous flow VADs (eg. HeartMate II (HMII)) have experienced gastrointestinal bleeding, in part caused by the proteolytic cleavage or mechanical destruction of von Willebrand Factor (vWF), a clotting glycoprotein. In vitro studies were performed to measure the flow located within the HMII outlet cannula under both steady and physiological conditions using particle image velocimetry. Under steady flow, a mock flow loop was used with the HMII producing a flow rate of 3.2 L/min. The physiological experiment included a pulsatile pump operated at 105 BPM with a stroke volume of 50 mL and in conjunction with the HMII producing a total flow rate of 5.0 L/min. Velocity fields, Reynolds normal stresses (RNS), and Reynolds shear stresses (RSS) were analyzed to quantify the outlet flow's potential contribution to vWF degradation. Under both flow conditions, the HMII generated principal Reynolds stresses that are, at times, orders of magnitude higher than those needed to unfurl vWF, potentially impacting its physiological function. Under steady flow, principal RNSs were calculated to be approximately 500 Pa in the outlet cannula. Elevated Reynolds stresses were observed throughout every phase of the cardiac cycle under physiological flow with principal RSSs approaching 1500 Pa during peak systole. Prolonged exposure to these conditions may lead to Acquired von Willebrand Syndrome, which is accompanied by uncontrollable bleeding episodes.

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