An experimental model of detrusor instability in the obstructed pig

Bladder outflow obstruction was produced in 18 young male pigs using either a silver ring or a silk ligature placed around the proximal urethra. Normal growth of the animals resulted in progressive obstruction. This was monitored by urodynamic studies in conscious animals, using either long-term indwelling bladder cannulae or by intermittent suprapubic catheterisation. At urodynamic assessment 3 to 5 months later, the obstructed pigs voided at an elevated pressure and with a diminished flow rate compared with control animals. Sixty-four per cent of the obstructed pigs developed detrusor instability, with spontaneous contractions exceeding 15 cm H2O during bladder filling; another 14% had decreased bladder compliance. In control animals the filling cystometrogram was stable, with little pressure rise during filling and no spontaneous contractions. This animal model provides the opportunity to study the physiological changes responsible for the development of detrusor instability in the obstructed bladder. It may also be useful for evaluating new treatment regimes for detrusor instability.