[Pressure-flow relationship at varying degrees of ureteral obstruction].

The effect of increasing ureteral stenosis on intrapelvic pressure and renal function was studied theoretically and experimentally. Assuming that ureteral flow is laminar, pressure drop across the stenosis can be calculated by Poiseuilles law. Based on this theoretical model, severe ureteral stenosis may be necessary to produce high intra-pelvic pressure at physiological urine flow rate. For instance, a 22G injection needle sized stenosis is necessary to increase intrapelvic pressure more than 20 mmHg at the flow rate of 10 ml/min. Pressure-flow relationship at varying degrees of stenosis at cut end of dog ureter was similar to that theoretically calculated. In contrast, even a mild stenosis with theoretically negligible resistance might cause a significant intra-pelvic pressure elevation and produced hydronephrosis with disturbance of sodium and water reabsorption, if it was created in the intact ureter. These results, together with previous experimental and clinical investigation, indicate that severe stenosis, which is rare in clinical hydronephrosis, should be necessary as a physical resistance to urine flow for significant increase of intra-pelvic pressure. We assume that functional cause may be predominant in most cases of clinical hydronephrosis.