Mechanical properties of the porcine bile duct wall

Ten normal porcine common bile ducts were examined in vitro. A computer-controlled volume ramp infusion system with concomitant pressure recordings was constructed. A video camera provided simultaneous measurement of outer dimensions of the common bile duct. Wall stresses and strains were computed.The common bile duct length increased by 25% from 24.4 ± 1.8 mm at zero pressure to 30.5 ± 2.0 mm at 5 kPa (p < 0.01). The diameter increased less than 10% in the same pressure range from 8.6 ± 0.4 mm to 9.3 ± 0.4 mm (p < 0.01). The stress-strain relations showed an exponential behavior with a good fit to the equation: σ = α . (exp(βε) - 1). The circumferential stress-strain curve was shifted to the left when compared to the longitudinal stress-strain curve, i.e. the linear constants (α values) were different (p < 0.01) whereas the exponential constants (β values) did not differ (p > 0.5).The porcine bile duct exhibited nonlinear anisotropic mechanical properties.The function of the common bile duct is to transport the bile from either the gall bladder or the liver to the duodenum by passing it through the sphincter of Oddi. The duct has been described as a passive conduit consisting mainly of connective tissue with a high collagen content and only few smooth muscle cells [1,2]. Contractions have been reported [3] but these may be retrograde projections of contractions from the sphincter of Oddi [1].Contractions of the gall bladder and relaxation of the sphincter of Oddi facilitate bile flow [4,5]. Hence, the bile duct can be considered as a pressure vessel without the ability to generate active forces by itself. Since the biliary tract is a distensible pressure vessel, it is important to obtain data on the mechanical wall properties. The mechanical properties will determine the behavior of the duct during loading and is likely to change in diseases of the biliary system. Few papers have focused on the biomechanical and morphometric properties of the bile duct wall. The li