Numerical modelling and analysis of blood flow through compliant, size-mismatched arterial anastomoses in reconstructive surgery.

ORCID

Abstract

Free tissue transfer in reconstructive surgery necessitates microsurgical anastomosis of arteries and veins. Size discrepancy between donor and recipient arteries can present a challenge for the microsurgeon, for which various anastomotic techniques are available. Thrombosis can be induced by regions of flow recirculation or stagnation. Metrics such as time-averaged wall shear stress (AWSS) and relative residence time (RRT) can quantify such flow conditions. Factors such as vessel size mismatch, anastomotic technique, resistance (and compliance) of the donor flap and pressures at the recipient site all influence these flow conditions. In this study, a numerical modelling methodology is developed to elucidate flow conditions at the arterial anastomosis site. Using a Fluid Structure Interaction (FSI) approach, a Computational Fluid Dynamics (CFD) model of non-Newtonian blood flow is coupled to a structural Finite Element Analysis (FEA) visco-hyperelastic model of the vessel wall. The CFD model incorporates a Windkessel representation of the donor flap, with a time-varying recipient pressure inlet (allowing the formation of Womersley inlet flow). The numerical model is validated against a range of analytical/experimental predictions. Model parameters (defining fluid properties, wall properties and all boundary conditions) are derived from a wide range of published data.Numerical model results are presented for typical reconstructive surgery applications, with three anastomotic techniques used to manage arterial diameter mismatch (invaginated, oblique and end-to-side). Results show that conditions for thrombosis (very low AWSS and very high RRT) are more pronounced in the invaginated case compared to the oblique case. Numerical model results are also presented for cases representative of a published experimental (rodent) study of arterial anastomosis with size mismatch. Despite the rodent vessels being a similar size to the human vessels of interest, their dissimilar position and function within the arterial network generate dissimilar flow conditions; minimum AWSS, maximum RRT and maximum shear stress typically differ by an order of magnitude compared to the human cases, demonstrating limitations of this rodent study in elucidating flow in human reconstructive surgery applications.

Document Type

Thesis

Publication Date

2024

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