This study was undertaken to evaluate the elasticity of gallbaladder in dogs. The pressure-volume relationship was determined b injecting various amounts of fluid into the gallbladder which was placed in a liquid paraffin bath, and the pressure within the gallbladder was observed in the excised fresh specimens and in the living dogs. The pressure at which the fluid started to leak were also determined. The results are summarized as follows.
1. The shape of the pressure-volume curve of dog´s gallbladder is hyperbolic in general, i.e., the pressure within he gallbladder remains essentially constant until the injected fluid reaches a certain limit and thereafter the pressure is increased sharply. This indicates that the gallbladder is an organ of poor distensibility.
2. The pressure-volume curve in the course of injecting and aspirating of fluid revealed hysteresis phenomenon, i.e., the pressure when the fluid was injected was always greater than that when the fluid was aspirated under the same volume of the gallbladder.
3. To describe the elasticity of the gallbladder quantitatively, the concept of compliance was introduced. The compliance was calculated from the slope at the nearly linear portion of pressure-volume curve, i.e., 50 cmH_2O when the fluid was injected. The mean values of compliance in the excised specimens and living specimens are 0.082 and 0.147 ml/cmH_2O respectively.
4. The relationship between tension developed in the wall of the gallbladder and the length of circumference of the gallbladder was determined by Laplace law assuming the inflated gallbladder was a sphere. The tension in the wall of living gallbladder is greater than that of the excised specimens under the same volume, and the latter has greater wall tension and greater volumes than the former under the same pressure. Such a difference between the living and excised specimens is attributed to the active contraction and/or tonus of the bladder wall in the living animal. In addition, the contracting function or the tonus of the gallbladder seems to be important for not only evacuation of bile but also for maintaining the gallbladder volume small so as to prevent the over distension and possible mechanical damage.
5. When the pressure in the gallbladder reached to a certain level the leakage of the fluid was observed. The mean leakage pressure is approximately 23 cmH_2O, though the variation is rather great. This leakage of fluid through the wall of the gall bladder is probably due to the mechanical damage caused by over distension of the bladder wall.
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