Aortic heart valves and their replacements fail in vivo for reasons that are not fully
understood. Mechanical evaluation and simulations of the function of native aortic
valves and their replacements have been limited to tensile and biaxial tests that seek to
quantify the behavior of leaflet tissues as a homogenous whole. However, it is widely
understood that valvular tissues are multi-layered structures composed of collagen,
elastin, and glycosaminoglycans. The mechanical behavior of these layers within intact
valve leaflet tissues and their interactions are unknown. In addition, pulmonary valves
have been used as substitutes for diseased aortic valves without any real understanding of
the mechanical differences between the aortic and pulmonary valves. The pulmonary
valve operates in an environment significantly different than that of the aortic valve and,
thus, mechanical behavioral differences between the two valve leaflets may exist. In this
study, we sought to determine the mechanical properties of the porcine aortic and
pulmonary valves in flexure, and to determine the mechanical relationship between the
leaflet layers: the fibrosa, spongiosa, and ventricularis. This was accomplished by
developing a novel flexure mechanical testing device that allowed for the determination
of the flexural stiffness of the leaflet tissue was determined using Bernoulli-Euler
bending. Moreover, transmural strains were quantified and used to determine the
location of the neutral axis to determine if differences existed in the layer properties of
the fibrosa and ventricularis. To contrast the flexural studies, biaxial experiments were
also performed on the aortic and pulmonary valves to determine the mechanical
differences in the tensile behavior between the two leaflets.
Results indicated that the pulmonary valve is stiffer than the aortic valve in
flexure but less compliant than the aortic valve in biaxial tensile tests. The interactions
between the layers of the leaflets suggest an isotropic mechanical response in flexure, but
do so through mechanisms that are not fully understood. For heart valve leaflet
replacement therapy, this study illustrates the biomechanical differences between the
aortic and pulmonary valve leaflets and emphasizes the need to fully characterize the two
as separate but related entities. Understanding the interactions of microscopic structures
such as collagen and elastin fibers is critical to understanding the response of the tissue as
a whole and how all these elements combine to provide a functioning component of the
organ system.
| Identifer | oai:union.ndltd.org:PITT/oai:PITTETD:etd-12032004-103650 |
| Date | 28 January 2005 |
| Creators | Lam, Thanh V |
| Contributors | Dr. Michael Sacks, Dr. Hai Lin, Dr. Richard Debski |
| Publisher | University of Pittsburgh |
| Source Sets | University of Pittsburgh |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.library.pitt.edu/ETD/available/etd-12032004-103650/ |
| Rights | unrestricted, I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to University of Pittsburgh or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
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