The effect of urinary flow and bladder fullness on renal pelvic pressure in a rat model.

We describe an in vivo animal model used to study the interactions of urinary flow, and bladder pressure and fullness on renal pelvic pressure. These parameters were examined in 17 nonrefluxing Sprague-Dawley rats. At urinary flow rates less than 14 cc/kg. per hour and bladders less than 60% full, renal pelvic pressures were below 9 cm. water but at urinary flow rates more than 30 cc/kg. per hour renal pelvic pressure increased above 10 cm. water when the bladder was only 20% full. At all urinary flow rates examined renal pelvic pressure increased to more than 20 cm. water as the bladder approached 100% fullness. To quantitate the combined effects of these changes in renal pelvic pressure and urinary flow on the renal pelvis a renal pelvic work index (renal pelvic pressure times urinary flow rate) was defined. Using this index the magnitude of the change between low urinary flows with an empty bladder and high urinary flows with a full bladder can be observed. The results of these studies in this model might be applicable to high urinary flow states or bladders that fail to empty completely.