A Fluid Dynamic Study of the Effect of Hematocrit in the 12 cc Penn State Pediatric Ventricular Assist Device

Open Access
Author:
Silver, Jeremy Michael
Area of Honors:
Bioengineering
Degree:
Bachelor of Science
Document Type:
Thesis
Thesis Supervisors:
  • Keefe B Manning, Thesis Supervisor
  • Keefe B Manning, Honors Advisor
  • William O Hancock, Faculty Reader
  • Peter J Butler, Faculty Reader
Keywords:
  • ventricular assist device
  • pediatric
  • cardiovascular device
  • hematocrit
  • thrombosis
  • particle image velocimetry
  • piv
  • VAD
  • PVAD
Abstract:
As part of the continuing development of the Penn State 12 cc pulsatile pediatric ventricular assist device (PVAD), this study focused on examining the effect of hematocrit on the fluid dynamics within the device. Hematocrit is defined as the ratio of the volume of packed red blood cells to total blood volume. Changes in hematocrit have a considerable effect on the viscoelastic properties of blood and can alter the fluid dynamics throughout circulatory support devices like the PVAD. Unlike adults that generally have a more consistent hematocrit, the pediatric population has been shown to have a more varied hematocrit range anywhere from 20%-60%. Additionally, the animals used for PVAD testing tend to have a comparatively low hematocrit in the 20%-30% range. For this study, three different non-Newtonian blood analogs were created to match the viscoelastic properties of 20%, 40% and 60% hematocrit pediatric blood. These fluids were then used in an in vitro mock circulatory loop designed to mimic the pediatric circulatory system. In order to examine the effect of hematocrit on the flow through the PVAD, planar particle image velocimetry (PIV) was used to develop whole field velocity profiles. These fluid dynamic measurements helped to describe the flow both quantitatively and qualitatively throughout the cardiac cycle. The changes observed in the flow field of the different hematocrit blood analogs are important because flow characteristics like stagnation and turbulent flow have the potential to increase the chances of clot formation, cause blood damage, and disrupt flow. While the general flow pattern within the PVAD was similar, the varying blood analogs created distinct inlet/outlet jets and rotational flow patterns. Specifically, the 20% hematocrit blood analog created a slightly higher peak velocity inlet jet that penetrated deeper into the blood sac earlier in the cardiac cycle. The more viscoelastic fluid, the 60% hematocrit blood analog, created an inlet jet that developed later and was maintained longer into the cardiac cycle, resulting in a more delayed rotational flow pattern. This delay continued into systole and resulted in a lower velocity outlet jet in the more viscoelastic fluids. It is clear that changes in hematocrit alter the fluid dynamics in the PVAD. Understanding the exact effect of hematocrit on the PVAD flow helps to understand animal testing data and guide future use of the device in pediatric patients in a hematocrit range of 20%-60%.