A Myocybernetic Model of the Lower Urinary Tract

A biomechanical model of the lower urinary tract which is able to respond to input signals from a neural network is presented. The neural input is the starting point in the description of the relationships between the various physical parameters in the mechanical model of the bladder and the urethra. The cybernetics of the lower urinary tract are described on the basis of the muscle dynamics of single models of both the detrusor in the bladder wall and the urethral sphincter. The urethral sphincter is not described as a variable resistance, like in other biomechanical models of the lower urinary tract, but is described on the basis of striated muscle dynamics. The forces produced by the detrusor and the urethral spincter give rise to the bladder pressure and the urethal pressure. Using quasi-steady assumptions, the flow rate of urine is calculated as a result of the pressure difference between the bladder ad the urethra. Parameters like the bladder volume, the flow rate and the pressure in the bladder can be compared with clinical data of urodynamic measurements. Simulation results show that the model is able to mimic both a filling and an emptying behaviour which resembles the behaviour of the lower urinary tract. By increasing the resistance of the urethra, a behaviour model of the lower urinary tract appears which is comparable with the pathology of urethral obstruction. A sensitivity analysis of various parameters in the model leads to a better understanding of the biomechanics of the lower urinary tract.