Pittaccio, Simone; (2004) Contribution to the fluid dynamic study of reconstructed aortic arch. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

INTRODUCTION: Coarctation of the aorta (CoA) is a congenital malformation consisting in a severe narrowing of the upper descending aorta, that generates a localised pressure drop. After surgical repair, patients may present residual and/or recurrent haemodynamic problems. This thesis quantitatively compares the outcomes of surgery performed by end-to-end anastomosis (E/E), Gore-tex graft interposition (GGI) and Gore-tex graft aortoplasty (GPGA) with pre-operative and control conditions. METHODS: Magnetic resonance imaging (MRI) was used to acquire morphology and blood velocities from swine models acutely and at four-months post-operatively. The aortic wall mechanical properties were assessed from mechanical tests on the tissues of these animals. The data were analysed and partly used to create computational fluid dynamics (CFD) models comprising a rigid-wall simulation of healthy descending aorta with realistic geometry and inflow data; MRI-based compliant-wall simulations of the repairs with multiscale-approach active afterload; compliant-wall axi-symmetric models of the pre-and post-operative conditions with multiscale active body circulation response. RESULTS: These different approaches yielded information on local haemodynamics and pressure/power losses; the evolution of diagnostic parameters as the radio-femoral gradient; the systemic impact of localised surgery; the effects of collateral circulation; the aortic wall mechanics and the effect of tissue interfaces. From the engineering viewpoint methodologies were developed for arterial geometry reconstruction, the use of MRI blood velocity datasets in CFD, the creation of complex models including fluid-structure interaction alongside multiscale coupling. An index for power dissipation and a model for suture line stiffness were also proposed, As a result of this study, E/E appears to be quantitatively most similar to the healthy state. CONCLUSIONS: It is hoped that this thesis will contribute to both clinical research and to Bioengineering applications. Further study and increased computer power could allow for the use of better approximations to the real material characteristics in CFD simulations.

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