A finite deformation theory of intravesical pressure and mural stress of the urinary bladder.

The urinary bladder is assumed to be an incompressible isotropic material like a rubber. Then, by making use of the finite deformation theory for such a hyperelastic continuum, we have calculated the intravesical pressure and the mural stress of the bladder as a function of its volume. The formula for the mural stress contains two parameters. These parameters are determined by the uniaxial extension test of the dog bladder sample. The calculation result shows that the pressure is relatively flat while the stress continues to rise with the volume. This is the typical behavior in the normal living cystometrogram. From these analysis, therefore, we conclude that such a behavior comes from the elasticity of the bladder itself, and requires no explanation in terms of reflex inhibitory relaxation.