Evaluation of valve function in antireflux biliary metal stents

To overcome duodenobiliary reflux induced by biliary stents, antireflux valve (ARV) biliary stents have been developed and showed improvement in stent patency. However, negative study results have also been reported because stent patency may be decreased by the malfunction of ARV itself. Given such mixed results, the true efficacy of ARV remains unknown and the mechanism of its dysfunction needs to be clearly elucidated. The aim of this study was to investigate the exact mechanism of ARV dysfunction using in vitro phantom models. Two experimental models were designed to evaluate two important environmental factors suspected to cause ARV malfunction, i.e. bile flow and pH. Three types of ARV metal stents from different companies were used for the experiments: a funnel type ARV, a windsock type ARV, and a wine glass-shaped ARV. Ten stents of each type were tested (five stents in the bile flow phantom model, and another five stents in the duodenal pH environmental model). To determine ARV malfunction, ARV-induced flow resistance was measured using a custom-made testing device. All stents from the two models were removed every 2 weeks for 12 weeks after stent insertion and were evaluated on morphological and functional changes of the ARV. Only ARV of wine glass-shaped ARV was morphologically changed due to silicone bond detachment in the bile flow model. All types of ARV were morphologically changed in the pH model. The morphological changes of ARV influenced the flow resistance. The antegrade pressure gradients were increased over time in the pH model (p