In pigs under general anesthesia, the mutual relation between ureterovesical flow and detrusor activity was evaluated with juxtavesical ureteral perfusion pressure measurements and cystometry. At constant bladder filling volume ureterovesical perfusion could provoke detrusor activity, which was positively related to the perfusion rate, and which disappeared after perfusion was stopped. During such involuntary detrusor activity ureterovesical perfusion pressure might increase significantly more than intravesical pressure. It is concluded that ureterovesical flow causes distension of detrusor muscle bundles around the ureteric hiatus, which may trigger local and general detrusor activity in an unstable bladder. During such detrusor activity, due to forces in the bladder wall, resistance to outflow from the upper urinary tract could be significantly more impaired than is reflected by the increase of intravesical pressure at cystometry. The clinical implications are discussed.

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