Computational analysis of the flow of bile in human cystic duct.

Computational fluid dynamic (CFD) simulations of the three-dimensional flow structures in realistic cystic ducts have been performed to obtain quantitative readings of the flow parameters to compare with clinical measurements. Resin casts of real patients' cystic ducts lumen that possess representative anatomical features were scanned to obtain three-dimensional flow domains that were used in the numerical analysis. The convoluting nature of the studied cystic ducts resulted in strong secondary flow that contributed towards a dimensionless pressure drop that is four times higher than those of a straight circular tube of an equivalent length and average diameter. The numerical pressure drop results across the cystic duct compared very well with those obtained from clinical observations which indicate that CFD is an appropriate tool to investigate the flow and functions of the biliary system. From the hydrodynamic point of view, the cystic duct lumen seems to serve as a passive resistor that strives to provide a constant amount of resistance to control the flow of bile out of the gallbladder. This is mainly achieved by the coupling of the secondary flow effects and bile rheology to provide flow resistance.

Investigation of the functional three-dimensional anatomy of the human cystic duct: a single helix?

Clinical research into the formation of gallstones has indicated that the anatomy of the cystic duct is one of a number of factors contributing to the formation of gallstones. The cystic duct allows low-viscosity hepatic bile to enter the gallbladder under low pressure and the expulsion of a more viscous gallbladder bile, but little is known about this transport mechanism and the effect of anatomical variations in structure. This article describes the variation in geometry of the cystic duct, obtained from acrylic resin casts of the neck and first part of the cystic duct in gallbladders removed for gallstone disease and obtained from patients undergoing partial hepatectomy for metastatic disease. The data obtained allowed us to formulate a number of standard terms for describing cystic duct morphology and demonstrate that the term "spiral valve" is only partially correct when describing the duct anatomy. In over half of the casts, spiraling was not the dominant feature of the cystic duct. Additionally, the term valve implies active resistance to flow in one direction, whereas the internal baffles of the cystic duct would serve to regulate bile flow in both directions. These data are useful for realistic 3D modeling of fluid-structure interactions of the flow of bile in the human cystic duct.

The flow of bile in the human cystic duct.

Clinical studies suggest that the flow of bile in the biliary system may be a contributing factor in the pathogenesis of cholelithiasis, but little is known about its transport mechanism. This paper reports a numerical study of steady flow in human cystic duct models. In order to obtain parametric data on the effects of various anatomical features in the cystic duct, idealised models were constructed, first with staggered baffles in a channel to represent the valves of Heister and lumen. The qualitative consistency of these findings are validated by modelling two of the real cystic ducts obtained from operative cholangiograms. Three-dimensional (3D) models were also constructed to further verify the two-dimensional (2D) results. It was found that the most significant geometric parameter affecting resistance is the baffle clearance (lumen size), followed by the number of baffles (number of folds in the valves of Heister), whilst the least significant ones are the curvature of the cystic duct and the angle between the neck and the gallbladder. The study presented here forms part of a larger project to understand the functions of the human cystic duct, especially the influence of its various anatomical structures on the resistance to bile flow, so that it may aid the assessment of the risk of stone formation in the gallbladder.