In-vivo heterogeneous functional and residual strains in human aortic valve leaflets

Aggarwal, A. , Pouch, A. M., Lai, E., Lesicko, J., Yushkevich, P. A., Gorman III, J. H., Gorman, R. C. and Sacks, M. S. (2016) In-vivo heterogeneous functional and residual strains in human aortic valve leaflets. Journal of Biomechanics, 49(12), pp. 2481-2490. (doi: 10.1016/j.jbiomech.2016.04.038) (PMID:27207385) (PMCID:PMC5028253)

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Residual and physiological functional strains in soft tissues are known to play an important role in modulating organ stress distributions. Yet, no known comprehensive information on residual strains exist, or non-invasive techniques to quantify in-vivo deformations for the aortic valve (AV) leaflets. Herein we present a completely non-invasive approach for determining heterogeneous strains – both functional and residual – in semilunar valves and apply it to normal human AV leaflets. Transesophageal 3D echocardiographic (3DE) images of the AV were acquired from open-heart transplant patients, with each AV leaflet excised after heart explant and then imaged in a flattened configuration ex-vivo. Using an established spline parameterization of both 3DE segmentations and digitized ex-vivo images (Aggarwal et al., 2014), surface strains were calculated for deformation between the ex-vivo and three in-vivo configurations: fully open, just-coapted, and fully-loaded. Results indicated that leaflet area increased by an average of 20% from the ex-vivo to in-vivo open states, with a highly heterogeneous strain field. The increase in area from open to just-coapted state was the highest at an average of 25%, while that from just-coapted to fully-loaded remained almost unaltered. Going from the ex-vivo to in-vivo mid-systole configurations, the leaflet area near the basal attachment shrank slightly, whereas the free edge expanded by ~10%. This was accompanied by a 10° −20° shear along the circumferential-radial direction. Moreover, the principal stretches aligned approximately with the circumferential and radial directions for all cases, with the highest stretch being along the radial direction. Collectively, these results indicated that even though the AV did not support any measurable pressure gradient in the just-coapted state, the leaflets were significantly pre-strained with respect to the excised state. Furthermore, the collagen fibers of the leaflet were almost fully recruited in the just-coapted state, making the leaflet very stiff with marginal deformation under full pressure. Lastly, the deformation was always higher in the radial direction and lower along the circumferential one, the latter direction made stiffer by the preferential alignment of collagen fibers. These results provide significant insight into the distribution of residual strains and the in-vivo strains encountered during valve opening and closing in AV leaflets, and will form an important component of the tool that can evaluate valve׳s functional properties in a non-invasive manner.

Item Type:Articles
Additional Information:This work was supported by American Heart Association, United States (Grant no. 14POST18720037 to A.A.), Welsh Government and Higher Education Funding Council for Wales through the Sêr Cymru National Research Network in Advanced Engineering and Materials (Grant no. F28 to A.A.), and National Institutes of Health, United States (Grant no. R01 HL108330 to M.S.S and HL119010 to Dr. Pouch).
Glasgow Author(s) Enlighten ID:Aggarwal, Dr Ankush
Authors: Aggarwal, A., Pouch, A. M., Lai, E., Lesicko, J., Yushkevich, P. A., Gorman III, J. H., Gorman, R. C., and Sacks, M. S.
College/School:College of Science and Engineering > School of Engineering > Infrastructure and Environment
Journal Name:Journal of Biomechanics
ISSN (Online):1873-2380
Published Online:06 May 2016
Copyright Holders:Copyright © 2016 Elsevier
First Published:First published in Journal of Biomechanics 49:2481-2490
Publisher Policy:Reproduced in accordance with the copyright policy of the publisher

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