URETHRAL ELASTICITY AND MICTURITION HYDRODYNAMICS IN FEMALES

The theory of the flow of an incompressible, inviscid fluid through an elastic tube is developed and applied to a simple model of the female urethra during micturition. The importance of the fact that the flow velocity is comparable with the velocity of longitudinal elastic waves on the urethra is stressed. Flow rates and urethral profiles at different bladder pressures are calculated and found to agree qualitatively with experimental observations. In particular, it is shown that an elastic constriction near the mid-point of the urethra leads directly to an asymmetrical profile, funnelling down from the bladder neck to the constriction, and remaining narrow between the constriction and the external meatus, even in a urethra elastically symmetrical about the constriction. It is shown that the flow rate is governed by the elastic properties of the constriction, and that the effect of viscosity on the flow is relatively small, justifying the idealization that the fluid is inviscid. © 1969 International Federation for Medical and Biological Engineering.