In an effort to define a more physiological method to determine obstruction in the upper urinary tract, the technique of constant pressure perfusion was studied in the canine and porcine models. In contrast to the constant flow technique of Whitaker, constant pressure perfusion is independent of upper tract compliance, uses low fixed pressures (7 to 12 cm. water) in the renal pelvis and measures flow rates from the upper tracts. In the canine and porcine models constant pressure perfusion demonstrated increased sensitivity and better discrimination between normal and partially obstructed systems relative to constant flow. Pressures in nonobstructed canine and porcine renal pelves are normally low (less than 8 cm. water) for flow rates into the bladder of 1 to 5 cc per minute. When using constant pressure perfusion in systems with partial distal ureteral obstruction, low or no flow is appreciated across the obstruction at renal pelvic pressures of 7 to 12 cm. water. By constant flow obstruction is defined in the same systems but only after renal pelvic pressures exceed 15 to 20 cm. water. We believe that there is clear clinical applicability.
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