Time course of ureteral changes with obstruction.

Chronic obstruction is characterized by a marked degree of ureteral dilatation and tortuosity which develops in the presence of a relatively low intraluminal pressure. To define the mechanism for the development of this relationship, the pressure-tension-deformation relationships of acute and chronically obstructed ureters were investigated. Rabbit ureters, in vivo, were obstructed and deformation correlated with intraluminal pressure. During the initial 3 h of obstruction, ureteral resting pressure increased from approximately 0 to 42 cm H2O, and diameter increased 16% with a slight increase in length. Subsequently, average wall tension (tensile stress) and intraluminal pressure declined, although deformation persisted. Between 6 h and 8 days after the onset of obstruction, intraluminal pressure remained essentially unchanged. During this time interval, ureteral deformation continued gradually and progressively as the ureter underwent creep both circumferentially and longitudinally. This was associated with a marked increase in average wall tension. At 8 days the diameter had increased by 170% and the length by 25%.