Experimental study of ureteral calculus disease: effects of calculus size, obstruction and hydration.

A chronic canine model was developed to study the immediate mechanical effects of ureteral calculi. Totally implanted nephrostomy tubes were used to measure renal pelvic pressure and optical sensors recorded ureteral activity. Surrogate calculi were inserted in a retrograde fashion via a trigonal vesicostomy. Complete obstruction was more common with larger calculi and these all passed spontaneously, by which time ureteral activity had ceased. Reduction in urine output delayed the rise in renal pressure and thus prolonged the time the calculus was retained in the ureter. If large calculi, which normally obstruct, had holes drilled in them to allow free urine flow they remained in the ureter for at least 2 hours and had to be extracted. Therefore, in the first few hours increased proximal hydrostatic pressure was the most important factor responsible for the spontaneous passage of obstructing calculi.