Mechanical properties of the porcine bile duct wall

BACKGROUND AND AIM The function of the common bile duct is to transport bile from the liver and the gall bladder to the duodenum. Since the bile duct is a distensible tube consisting mainly of connective tissue, it is important to obtain data on the passive mechanical wall properties. The aims of this study were to study morphometric and biomechanical wall properties during distension of the bile duct. METHODS 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. RESULTS 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: sigma = alpha x (exp(betaepsilon) - 1). The circumferential stress-strain curve was shifted to the left when compared to the longitudinal stress-strain curve, i.e. the linear constants (alpha values) were different (p < 0.01) whereas the exponential constants (beta values) did not differ (p > 0.5). CONCLUSION The porcine bile duct exhibited nonlinear anisotropic mechanical properties.