PURPOSE: We define the relationship of renal pelvic and bladder pressures with varying urinary flow rates and bladder fullness in unobstructed rats with and without vesicoureteral reflux. MATERIALS AND METHODS: Sprague-Dawley rats (180 to 250 gm.) were evaluated for vesicoureteral reflux followed by simultaneous and continuous renal pelvic and bladder pressure monitoring during bladder filling cycles. RESULTS: The incidence of congenital right vesicoureteral reflux was 25% (14 of 57 rats, below bladder pressure of 40 cm. water). The renal pelvic pressure was significantly higher in rats with reflux compared to normal rats only at very low urine output when the bladder was 90% full or greater and when the urine output was moderate with the bladder 50% full or less. For all other urine outputs and degrees of bladder fullness, there were no significant differences in pelvic pressure between rats with and without reflux. CONCLUSIONS: Renal pelvic pressures in the refluxing and nonrefluxing collecting system of rats with mild to moderate reflux do not differ except under well-defined conditions. Reflux can be induced by raising the intravesical pressure when the urinary flow rate is very low. Furthermore, vesicoureteral reflux pressures decrease post mortem. Therefore, the observation of vesicoureteral reflux is a relative phenomenon defined by urinary flow rate, bladder pressure and in vivo conditions, and one must define the specific bladder pressure and urinary flow rate that are present when reflux occurs. These data help explain why the observation of reflux may be intermittent or transient during various imaging studies.
PURPOSE: We define the relationship of renal pelvic and bladder pressures with varying urinary flow rates and bladder fullness in unobstructed rats with and without vesicoureteral reflux. MATERIALS AND METHODS:Sprague-Dawley rats (180 to 250 gm.) were evaluated for vesicoureteral reflux followed by simultaneous and continuous renal pelvic and bladder pressure monitoring during bladder filling cycles. RESULTS: The incidence of congenital right vesicoureteral reflux was 25% (14 of 57 rats, below bladder pressure of 40 cm. water). The renal pelvic pressure was significantly higher in rats with reflux compared to normal rats only at very low urine output when the bladder was 90% full or greater and when the urine output was moderate with the bladder 50% full or less. For all other urine outputs and degrees of bladder fullness, there were no significant differences in pelvic pressure between rats with and without reflux. CONCLUSIONS: Renal pelvic pressures in the refluxing and nonrefluxing collecting system of rats with mild to moderate reflux do not differ except under well-defined conditions. Reflux can be induced by raising the intravesical pressure when the urinary flow rate is very low. Furthermore, vesicoureteral reflux pressures decrease post mortem. Therefore, the observation of vesicoureteral reflux is a relative phenomenon defined by urinary flow rate, bladder pressure and in vivo conditions, and one must define the specific bladder pressure and urinary flow rate that are present when reflux occurs. These data help explain why the observation of reflux may be intermittent or transient during various imaging studies.