Ultrasonography in the assessment of gallbladder motor activity

Ultrasonography is an accurate and useful method for studying gallbladder volume variations and thus indirectly gallbladder emptying and refilling in humans. It has been shown that gallbladder main motor function is the result of a bellows-like mechanism with outflow and inflow of bile occurring during continuously alternating phases of gallbladder emptying and filling, that in turn lead to bile recycling within the gallbladder. Therefore, bile flux through the gallbladder cannot be properly expressed by time and rate of gallbladder emptying and gallbladder ejection fraction. In an attempt to analyse the gallbladder volume-hepatic bile flux relationship, simultaneous assessment of the gallbladder volume variations at ultrasonography and of the labelled bile in the gallbladder at cholescintigraphy during continuous infusion of an hydroxy iminodiacetic acid compound has been carried out. By applying a mathematical model to the analysis of gallbladder volume ultrasonography measurements, it is possible to measure the flux of bile through the gallbladder. By validating ultrasonography assessment of gallbladder volume variations with quantitative cholescintigraphy, it has been shown that the single non-invasive ultrasonography technique with serial frequent measurements of the gallbladder volume enables separate estimation of the flux of bile through the gallbladder in humans and in physiological conditions. In the postprandial state, hepatic bile was mainly: (1) stored in the gallbladder in a first phase; (2) emptied from the gallbladder in a second phase; and (3) stored in the gallbladder in a third phase. The amount of bile flowing bidirectionally through the cystic duct was about fivefold greater than that estimated with the usually employed variables, such as gallbladder ejection fraction or emptying and refilling delta volume. The mathematical analysis of minute-by-minute ultrasonography measurements of gallbladder volume variations yields both physiological and pathological insights. In healthy volunteers, it has been shown that: (1) caloric content of meals affects the total amount of bile recycled by the gallbladder; and (2) fat content of meals affects the modality of gallbladder emptying and refilling but does not affect the total amount of bile recycled by the gallbladder. In gallstone patients, a decreased turnover of bile has been shown which may contribute to cholesterol crystal precipitation and stone growth. In conclusion, unlike conventional variables used to assess gallbladder motor function such as gallbladder ejection fraction and rate of gallbladder emptying, mathematical analysis of frequent ultrasonography measurements of gallbladder volume variations enables non-invasive estimation of bile flow through the gallbladder in normal and abnormal physiological conditions.