VISUALIZATION OF THE OUTLET FLOW FROM THE HEARTMATE II LEFT VENTRICULAR ASSIST DEVICE USING LASER DOPPLER AND PARTICLE IMAGE VELOCIMETRY
Open Access
- Author:
- Rowlands, Grant William
- Graduate Program:
- Bioengineering
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- July 11, 2016
- Committee Members:
- Keefe B Manning, Thesis Advisor/Co-Advisor
Margaret June Slattery, Committee Member
William O Hancock, Committee Member - Keywords:
- Ventricular Assist Device
von Willebrand Factor
Fluid Dynamics
Heartmate II
Outlet Flow
Proteolytic cleavage
Laser Doppler Velocimetry
Particle Image Velocimetry - Abstract:
- Left ventricular assist devices (LVADs) are implanted in patients with a diseased ventricle to maintain peripheral perfusion or as a bridge to cardiac transplant. However, patients with an implanted LVAD, such as the HeartMate II (HMII), have experienced bleeding episodes in the abdomen. These incidents are likely caused by the cleavage or proteolytic breakdown of von Willebrand Factor (vWF), a protein in the clotting cascade. To determine the LVAD’s potential contribution to vWF mechanical destruction, in vitro studies were conducted to quantify the flow at the outlet of the HMII using particle image velocimetry (PIV) and laser Doppler velocimetry (LDV) under steady and pathophysiological conditions. In the steady flow experiment, the HMII was connected in series with a compliance chamber and operated at 8800 ± 100 RPM with an 80 mmHg rise across the pump, producing a flow rate of 3.2 ± 0.1 L/min. The second experiment included a pulsatile pump with the LVAD and compliance chamber inducing pulsatility through the HMII for a total flow rate of 5.0 ± 0.1 L/min. The pulsatile pump was operating at a rate of 105 beats per minute with a stroke volume of approximately 50 mL. Velocity profiles, Reynolds shear stresses (RSS), Reynolds normal stresses (RNS), and turbulence intensities (TI) were used to visualize the outlet flow in the cannula both quantitatively and qualitatively. Under both steady and pulsatile conditions, shear stresses orders of magnitude higher than those needed to unfurl and cleave vWF were observed in the outlet cannula. This evidence, in conjunction with high turbulence intensity values and stark contrasts in velocity profiles in certain regions, points to the positive correlation between continuous flow VADs and the potential proteolytic cleavage or mechanical destruction of vWF. Prolonged exposure of these flow conditions may lead to acquired von Willebrand Disease, which can lead to uncontrollable bleeding episodes in the abdominal region.