Urine flow curves of healthy males: a mathematical model of bladder and urethal function during micturition

Abstract

Previously isolated clinical and experimental observations on bladder and urethra are drawn together into a mathematical model of micturition. The urethra is treated as passively distensible, while the course of the flow rate is determined by the changing geometry of the actively contracting bladder. Numerical solution of the resulting equations, using independent clinical estimates of the majority of the parameters, shows that they can account for the observed features of the urine flow rate curves of healthy males. It appears that the series elasticity of the bladder muscle is important in maintaining a high flow rate down to low bladder volumes. A mechanical explanation of the peculiar character of micturitions from high initial bladder volumes is put forward. The bases of two clinical methods of assessing bladder function are clarified.