Intestinal flow after anastomotic operations in neonates.

Stagnation of contents at the anastomotic site for intestinal flows after anastomotic operation is a critical issue in neonates. Although various anastomosis methods have been developed, in the clinical field, poor passage at the anastomotic site in cases of jejunal atresia is still observed. A CFD study was carried out to clarify the reasons for the stagnation and to find favorable anastomosis methods from a fluid dynamical point of view. Direct numerical simulations were performed using OpenFOAM. The boundaries of the computational domain were peristaltically moved to reproduce flow. The results reveal that the peristaltic motion on the distal side dominates the flow and that on the proximal side has a negligible influence. In particular, the contents do not pass the anastomotic site when the peristaltic motion on the distal side is not active. The flow rate as a measure of the driving force of the flow on the proximal side is large when the amplitude of the peristaltic motion is large and the diameter is small. It was also found that anastomosis methods do not affect flow resistance.

Modification of hemodynamics in basilar artery aneurysm by the single and Y stent placement1.

BACKGROUND: Stent placement can change the hemodynamics in basilar artery aneurysms. However, the effects of the stent placement can depend on the angle of vessel bifurcation. OBJECTIVE: The hemodynamics in and near the aneurysm are investigated for two angles of vessel bifurcation and two stent models. Some statistical indexes are calculated to evaluate the effects of the stent placements on the possibility of aneurysm rupture. METHODS: Computational fluid dynamics simulations and phantom model experiments are performed. The angle between the basilar and posterior cerebral arteries is set to 90 and 135 degrees. The single stent and Y stent models are tested in addition to the case without stent placement. RESULTS: The velocity in the aneurysm in the Y stent case is smaller than that in the no stent and single stent cases when the angle is 135 degrees. High OSI and low AFI areas often appear at the same locations, and the area is larger in the single stent case than in the no stent and Y stent cases. CONCLUSIONS: The Y stent placement promotes hemostasis and thrombosis in the basilar artery aneurysm, whereas the single stent placement can enhance the growth and rupture.