The relationship between pressure and flow in the normal pig renal pelvis. An experimental study of the range of normal pressures.

The renal pelvis pressure flow relationship of 40 normal pig upper urinary tract was investigated. During standardized studies it was disclosed that the resting pressure has a normal distribution with wide 95% confidence limits (0.3-14.7 cmH2O). When perfusion was introduced, pelvic pressure increased, the normal distribution was lost, and the 95% confidence limits were broadened to more than 30 cmH2O. A normal distribution was regained at higher flow rates. The mean increment beyond 8 ml/minute was small, only 3.7 cmH2O from 8 ml/minute to 20 ml/minute. The wide variation found in pressure responses to high flow rates and the spread of pressures at higher flow rates imply major difficulties in distinguishing, between normal and abnormal pressure flow relationships in renal pelvis.