A Study of the Effect of Hematocrit on an Elevated Beat Rate in the 12cc Penn State Pediatric Ventricular Assist Device
Open Access
- Author:
- Houtz, Brady
- Graduate Program:
- Bioengineering
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- March 25, 2020
- Committee Members:
- Keefe B Manning, Thesis Advisor/Co-Advisor
William Joseph Weiss, Committee Member
William Hancock, Committee Member
William O Hancock, Program Head/Chair - Keywords:
- artificial heart
pediatric
hematocrit
ventricular assist device
cardiovascular fluid dynamics
elevated beat rate - Abstract:
- Ventricular assist devices (VADs) are used to treat heart failure by increasing the cardiac output while reducing the mechanical load experienced by the heart. The devices are often used as a bridge to transplantation device for patients on the organ transplant waiting list. With the success of these devices in adults, there has been a shift in focus towards developing VADs for pediatric patients. Previous studies have shown that certain flow conditions can increase the risk of thrombosis. This study analyzed the fluid dynamics in the 12 cc Penn State PVAD to gain a better understanding the risk of thrombosis. Changes in beat rate and hematocrit have been shown to influence the fluid dynamics within the PVAD. Prior studies have evaluated this device at 75 bpm with a blood analog matching 40% hematocrit blood despite average heart rates of 100 – 180 bpm and hematocrit levels of 20 – 60% in pediatric patients. This study aims to quantify the fluid dynamics in the PVAD at elevated beat rates and varying hematocrit using particle image velocimetry (PIV). The study used a mock circulatory loop and blood analog fluid to mimic pediatric cardiovascular conditions and the viscoelastic properties of blood. Three blood analog fluids were used to match the properties of blood at 20%, 40%, and 60% hematocrit, covering the full range of hematocrit levels that have been identified clinically. Two beat rates were examined, 75 bpm and 120 bpm, to examine the effects of an elevated beat rate. Flow and pressure waveforms were obtained to match physiologically relevant conditions. Particle image velocimetry was used to image the flow at three planes within the device, producing quantitative velocity maps. Each condition followed a similar flow progression throughout the cardiac cycle. Flow began with a strong inflow jet at the start of diastole, which transitioned into a solid body rotational flow through diastole. This rotational flow transitioned into an outlet jet during systole. Varying hematocrit had an effect on the development of these key flow characteristics at both beat rates. The more viscoelastic fluid created a stronger inflow jet, which led to a stronger recirculation region that was present later in systole. The 20% hematocrit fluid created a weaker inflow jet that dissipated early in systole, leaving more areas of low flow and stagnation. At the higher beat rate, similar flow patterns were observed. The increase in hematocrit further increased the strength and duration of the recirculation region.