Hydrodynamics of the Normal Multicalyceal Pyeloureter in Pigs: The Pelvic Pressure Response to Increasing Flow Rates, Its Normal Ranges and Intra-Individual Variations

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Abstract
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 1st was a low pressure phase between 0 to 2 ml/min where transport took place by peristalsis. The 2nd was a high pressure phase between 2 and 4 ml/min where the peristalsis opposed the passive interperistaltic filling of ureter. In the 3rd phase, between 4 and 6 ml/min, a decreasing pressure increment was seen, probably caused by leakage through the contraction ring. In the 4th 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; 14 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. Confidence limits (95%) 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 0-4 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. A comprehensive study of the pressure flow relationship provides new information concerning fluid transport in the upper urinary tract.