Determinants of progression and equilibrium in hydronephrosis.

Upper urinary tract urodynamic parameters were measured serially in 12 dogs subjected to partial ureteropelvic junction obstruction. Measurements of pressure-volume relationships (pelvimetrics) and the physiologic capacity of the renal pelvis were important predictors of hydronephrotic equilibrium which occurred only in kidneys whose pelvic urine volume remained lower than the renal pelvic capacity. Because of acquired changes in compliance and renal function, the same degree of obstruction caused progressive hydronephrosis at low pelvic volumes but not at high volumes in some kidneys. Hydronephrosis can thus be viewed as a compensatory mechanism which protects the kidney against further dilation and elevated intrapelvic pressure.