ABSTRACT
The gallbladder (GB) exhibits a hysteresis loop on its pressure-volume curves in vitro infusion-withdrawal experiments commonly. The loop indicates the viscoelasticity in intact GB walls, which can influence GB physiological refilling-emptying cycle. The effect has little been modelled in the literature. In the chapter, the viscoelasticity in the pressure-volume curves of guinea pig GBs was characterised in normal passive condition, active state stimulated with cholecystokinin (CCK), passive state but GB treated with indomethacin. The biomechanical model proposed includes three nonlinear springs, one contractile element, and one nonlinear dashpot in parallel phenomenologically. The slope of the experimental pressure-time curve serves as independent variable. The ratio of the work done on the viscous response in the loop to the elastic energy was defined, and the ratio and the stiffness of the elastic pressure-volume curve extracted were examined. The GB in active state has flat stiffness at low volume sharper stiffness at high volume as well as a large work-to-energy ratio (0.57–0.61) in comparison with the normal GB in passive state. CCK alters the biomechanical behaviour at large volume, indomethacin adjusts the GB wall property enterically.
