Date of Award

12-2009

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Legacy Department

Mechanical Engineering

Advisor

Figliola, Richard

Committee Member

Beasley , Donald

Committee Member

LaBerge , Martine

Committee Member

Hsia , Tain Yen

Abstract

Children born with congenital heart disease often times suffer from severe chronic pulmonary insufficiency. Palliative treatments for this condition may come early on in the life of the patient; however, if it becomes severe enough, a pulmonary valve replacement may be required. There currently is not a permanent option for a replacements valve. Therefore, a need exists to develop a permanent solution. Knowing that the right heart circulation is more tolerant of moderate levels of regurgitation (0 - 35%) and pressure gradient (0 - 30 mmHg), this study investigates the hypothesis that a fluid diode, a motionless valve that offers low resistance to forward flow and high resistance to reverse flow, could serve as a permanent solution.
The diode valve concept was tested in vitro in a mock pulmonary circulatory system (MPCS). Transvalvular pressure gradient (TVG) and regurgitant fraction (RF%) were used to assess valve performance. The valve was tested in vitro over a range of pulmonary vascular resistances (PVR). In vivo testing was completed using a swine model. A parametric study was also done to find the effect of changing geometries on the flow regulating capabilities of the valves. Finally, flow field studies were performed using particle image velocimetry (PIV). The flow patterns, viscous shear and Reynolds shear stresses were analyzed, and the potential for platelet activation and thrombus formation was determined.
In the in vitro studies, the fluid diode maintained the RF% between 2% and 17% and TVG less than 17 mmHg for PVR values between 1 and 5 mmHg/Lpm. The diode performed acceptably in the animal model as well for PVR between 2.3 and 3mmHg/Lpm and pulmonary vascular compliance (PVC) between 2 to 3 mL/mmHg. The parametric study identified the angle of impingement and beta ratio as two dimensions that affect the valve performance. The total shear stress level and exposure times were found using the PIV data. The level of activation was found to be a function of PVR and, for PVR values below 6 mmHg/Lpm, the threshold reported to trigger platelet activation was not exceeded.
As a whole, the study has shown that the diode valve concept shows promise as a replacement pulmonary valve. The fluid diode is capable of regulating flow to acceptable levels for some ranges of PVR and PVC.

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