Hydrodynamics of the normal multicalyceal pyeloureter in pigs: the pelvic pressure response to increasing flow rates, its normal ranges and intraindividual variations.

In 39 normal pig pyeloureters, pelvic pressure was measured at the following perfusion rates: 0, 2, 4, 6, 8, 10 and 20 ml./min. The mean pelvic pressure increased from 7.09 to 21.53 cm. H2O. This increase showed 4 different phases. The first was a low pressure phase between 0 to 2 ml./min. where transport took place by peristalsis. The second was a high pressure phase between 2 and 4 ml./min. where the peristalsis opposed the passive interperistaltic filling of ureter. In the third phase, between 4 and 6 ml./min., a decreasing pressure increment was seen, probably caused by leakage through the contraction ring. In the fourth phase, between 6 and 20 ml./min., the pressure was proportional to the flow rate and ureter functioned hydrodynamically as a tube. The measurements were performed bilaterally in 19 animals. Fourteen animals showed a difference either in baseline pressure or in mean perfusion pressure between the 2 sides; in effect, no coherence in pressure exists between the pyeloureters in the individual pig. Ninety-five per cent confidence limits of the pelvic pressure were calculated at the different flow rates. The limits of the baseline pressure were 1.43 and 12.75 cm. H2O, respectively. During perfusion the upper limit of normal pressures increased markedly in the flow range 0 to 4 ml./min. being 25.46 cm. H2O at 4 ml./min. A further increase in flow rate caused only a modest increase in the upper limit. It is concluded that a comprehensive study of the pressure flow relationship provides new information concerning fluid transport in the upper urinary tract.