Anti-reflux mechanism of an enteral extended biliary stent: a computational fluid dynamics study

Enterobiliary reflux is a significant risk factor for stent occlusion following endoscopic retrograde biliary drainage. This study used computational fluid dynamics (CFD) to compare traditional plastic biliary stents (PBSs) with enteral extended biliary stents (EEBSs), aiming to explain the prolonged patency observed with EEBS from a fluid dynamics perspective.

A three-dimensional digital model of the biliary tract, duodenum and the fluid domain was constructed. Using CFD, we numerically simulated fluid flow to analyze the pressure and velocity fields at the terminus of both PBS and EEBS. Flow field visualization techniques were employed to reveal the causes of reverse flow and assess the mechanisms of reflux.

Simulations revealed that PBS created a counter-directional pressure gradient at its terminus. The angled flow relative to intestinal contents caused flow stagnation and vortex formation, increasing reflux risk. In contrast, EEBS extends to the distal duodenum, aligning bile flow with intestinal contents. According to Bernoulli's principle, low-velocity bile at the EEBS tip forms a high-pressure zone, which synergizes with the high-velocity, low-pressure flow in the intestinal lumen to effectively suppress reflux.

The EEBS optimizes the flow field by extending the flow path and avoiding flow separation, which likely contributes to its prolonged patency. These findings provide a theoretical basis for designing anti-reflux stents. Future models should incorporate duodenal peristalsis to enhance physiological fidelity.