| This thesis presents a constitutive model of the mechanics of the urinary bladder in quasistatic states such as filling and isometric contraction.; To test the hypotheses that the passive urinary bladder is homogeneous and isotropic, I step-stretched strips cut from urinary bladders harvested from dogs and measured their force response. The strips were taken from different regions of the urinary bladder to test homogeneity and with different orientations to test isotropy. These preliminary data suggest that passive urinary bladder is homogeneous and isotropic and can be modelled with a single constitutive relation.; To test the assumption that the urinary bladder behaves as a sphere, I modelled the bladder as a prolate spheroid and an oblate spheroid with the same constitutive relation. I measured a filling pressure-volume relation (cystometrogram) on anesthetized dogs and used the sphericity assumption to deduce a constitutive relation. All spheroids have pressure-volume relations similar to that of a sphere with the exception of very eccentric oblate spheroids, which are more compliant.; The bladder undergoes biaxial stretch in vivo, so I used a strain energy function to derive both uniaxial and biaxial constitutive relations. I determined that the stress at each stretch in biaxial extension is only slightly higher than in uniaxial extension. Therefore, in vitro uniaxial extension experiments are a reasonable approximation of in vivo biaxial extension.; I used the model to study bladder hypertrophy due to outlet obstruction. Comparison of model results with data in the literature suggests that bladder hypertrophy due to mild outlet obstruction can be represented by an increase in wall mass, and bladder hypertrophy due to severe outlet obstruction can be represented by an increase in both wall mass and rest volume.; To determine if plastic deformation due to outlet obstruction can account for the inability to void after acute urinary retention, I simulated plastic deformation by increasing rest length. If the bladder undergoes a 26% increase in rest length due to its plastic deformation, it cannot generate a high enough pressure to overcome the urethral opening pressure and initiate emptying. |
