The development of detrusor instability in prostatic obstruction in relation to sequential changes in voiding dynamics.

We studied 34 patients with benign prostatic hypertrophy who had infravesical obstruction with a high opening pressure and a stable bladder. No treatment was given except for intermittent short courses of plant extracts. There were no factors other than prostatic obstruction that could affect the mechanics of micturition. The patients were reassessed after a mean of 21 months (range 7 to 62). Voiding dynamics were unchanged in 12 patients who had a stable obstructed bladder, while 22 had an unstable obstructed bladder with a significantly greater opening pressure. Peak flow pressure was also increased but much less so that at the onset of voiding. The driving pressure and bladder volume were decreased. Despite this fact, urine flow rates were unchanged and maximum external voiding power was enhanced. The significance of such findings is discussed.