The effects of valve leaflet mechanical properties on the dynamic geometry and function of the aortic heart valve are, to date, not well understood. This is largely due to the complex anatomy and solid-fluid interactions inherent in valve function. In the present study, the effects of leaflet stiffness on the dynamic aortic valve leaflet 3D geometry were quantified using a novel, non-contacting imaging system over the complete cardiac cycle. The imaging system utilized a structured laser-light imaging method, incorporated into a physiological flow loop, to project a high density matrix of laser dots onto the leaflet surface. The resulting dot pattern defined the leaflet surface, and was imaged by a pair of borescopes equipped CCD cameras providing stereographic views. From the image pairs, 3D dot coordinates were recovered using the direct linear transformation method. Five native porcine aortic heart valves were imaged, and then mechanically stiffened using a 0.625% aqueous glutaraldehyde fixation for 24 hours while under 4 mmHg transvalvular pressure. The valve was then re-imaged under near-identical flow conditions. Area, dimensional, surface curvature, and measurements were performed. We observed that: 1) the native valve elongates in the radial direction by ~30% when fully opened, and exhibited small, high frequency shifts in shape; 2) the stiffened leaflet demonstrated a more stabile shape, as well as focal regions of prolonged, high curvature; 3) the stiffened leaflet opens and closes faster by ~10 ms compared to native leaflet; 4) for both native and stiffened states, the aortic valve opened from basal region leading to free edge 5) when closing, both the native and stiffened state valve close with both free edge and circumferential together. Clearly, valve leaflet undergo complex geometric changes during the cardiac cycle, and leaflet mechanical properties (mainly stiffness) have a profound affect on leaflet dynamic geometry.
Overall, the primary findings of this study were the extensive radial distension in the native state, and that an increase in leaflet mechanical stiffness induces high bending areas. The physiological function and advantage of the radial distension is currently unknown, but may affect the local hemodynamic patterns during valve operations, especially in the sinus regions. Our findings for the stiffened tissue have implications to valve design. For example, the high bending observed in the stiffened state correlated with known locations of tissue deterioration previously reported in our laboratory. Thus, in order to minimize leaflet tissue damage, methods of chemical modification utilized in bioprosthetic heart valves that maintain leaflet flexibility are necessary to minimize the onset and progression of tissue damage.
| Identifer | oai:union.ndltd.org:PITT/oai:PITTETD:etd-04182003-160510 |
| Date | 12 May 2003 |
| Creators | Sugimoto, Hiroatsu |
| Contributors | Michael S. Sacks, George D. Stetten, James F Antaki |
| 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:80/ETD/available/etd-04182003-160510/ |
| 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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