Model of the female urethra: Part 2—Flow properties

We have used a series of urethral models to test a theory of flow through distensible tubes having a pressure maximum (elastic constriction) near the midpoint. From measurements of pressure head and flow rate the properties of each elastic constriction have been deduced by means of the theory, and have been compared with those known from static measurements (paper I). For models with a sufficiently broad elastic constriction the theory is correct. Increasing departures occur as the elastic constriction becomes more sharply localised. In particular, pressures measured by a static method, similar to the Brown-Wickham method used clinically, become greater than those deduced from the flow measurements. Similar behaviour is expected for the real urethra, and may be important in the understanding of incontinence. These models show the negative-resistance behaviour believed to be characteristic of sharply localised elastic constrictions.