BackgroundTo 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.MethodsTwo 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.ResultsOnly 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 < 0.05).ConclusionsMorphological change of the ARVs may induce dysfunction of ARV metal stents, which is mainly due to duodenal pH environment. In the future, development of new ARV that is not affected by duodenal environmental factors can be expected to improve stent patency.Electronic supplementary materialThe online version of this article (10.1186/s12876-018-0878-8) contains supplementary material, which is available to authorized users.

Recently, many buildings were large size, complex and high rise. The attention has been being increased for the safety of the building occupants. It caused the government to enact the new law or enhance the exiting law related with the high-rise building. But the scattered regulations with individual laws confused to apply the regulations. So this study are proposed the improvement direction for the high-rise building laws through the comparative analysis among the high-rise building laws. There were the highrise building laws like Building Act, Fire-fighting system installation business Act, Installation·maintenance and safety control of fire-fighting system Act, etc. The elicited problems among the high-rise buildings laws were mixed regulations in the individual laws, the different standard in the same regulation, the ambiguity between the law and a local government guideline. On the basis of them, this study suggested the improvement direction like as the integrated design guidelines for high-rise buildings, the unified standard for the same regulation, the introduced performance based design for the evacuation.

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