Analytical modeling and numerical simulation of forces in an endoluminal graft

Purpose: To utilize mathematical analysis and computational fluid dynamics (CFD) to investigate the forces acting within the pressurized aorta and upo n a stent-graft and how these forces may affect the ongoing performance of the stent-graft. Methods: Analytical force balance analysis and CFD simulations using the Fl uent code were used to mimic blood flow through a bifurcated stent-graft in a person at rest. Steady-state blood flow was assumed in which the inlet p ressure approximated the mean blood pressure (100 mm Hg) and the blood flow velocity was an approximation of the peak systolic flow rate (0.6 m/s). Tw o sizes of endoluminal grafts were analyzed: the larger graft had an inlet diameter of 3 cm and outlet diameters of 1 cm; the smaller graft diameters measured 2.4 cm proximally and 1.2 cm distally. The endografts were studied in 2 configurations: with the limbs straight and with one bent. Results: For the larger graft model, the normal peak blood flow induced a d ownward force of 7 to 9 N on the bifurcated grafts. Bending one of the limb s of the graft produced a sideways force of 1.3 N. For the smaller endograf t, the downward force was in the range of 3.1 to 5.1 N and the sideways for ce on a curved limb was similar to1.5 N. The magnitude of the forces given by the analytical formulae and the CFD results agreed to within 2 significa nt figures. Conclusions: These results suggest that the downward force on a bifurcated stent-graft, which may exceed the force required to dislodge it when relyin g on radial attachment alone, is determined mostly by the proximal graft di ameter. Curvature of the graft limbs creates an additional sideways force t hat works to displace the distal limbs of the graft from the iliac arteries .