Physical and mathematical modeling of the lower urinary tract: preliminary results

Urodynamic investigations are a highly specialized and sophisticated methods for the purpose of defining the func- tional status of the lower urinary tract. Urodynamic studies should assess micturition cycle, both the filling and the voiding phase. Urodynamic measurements are currently used in a series of conditions to determine the activity of detrusor muscle, to evaluate a voiding dysfunction (mainly related to obstructed voiding), or to monitor a disease progression, or the efficacy of a therapy. In case of possible diagnosis of bladder outlet obstruction (BOO) the main investigations include uroflowmetry and pressure-flow study. Various methods of analysis of pressure-flow data have been proposed. The classical nomograms by Abrams, Griffith or Scha€fer used to interpret the urodynamic measurements are essentially derived on an empirical basis. In order to improve the physical understanding of the lower urinary tract, the present study is aimed at investigating the fluid mechanic processes within the urethra by using a mathematical model based on the continuity and flow equa- tions of motion of an incompressible fluid in a collapsible/ distensible tube. To model adequately the fluid-structure interaction, the properties of the deformable tube and the surrounding organs must be known. Unfortunately, there are very few non-invasive measurements on the mechanical behavior of the lower urinary tract, and that’s because the structure of the urethra-bladder system and its relation with adjacent organs make its mechanical behavior rather compli- cated. Hence, a physical model has been designed and implemented in order to study the main relationships within the hydrodynamic variables. Notwithstanding the simplified structure, the model is able to preserve some main character- istics; in particular, it correctly simulates the main physical processes inside the lower urinary tract: the resistance to motion of the urethral walls, their deformability varying the intramural pressure, localized and distributed obstructions. In the present paper, the preliminary experimental results obtained from this laboratory model of the urethra are presented.