The biomechanical principles of upper urinary tract pressure-flow studies.

An experimental model is described in which the relationship between relative renal intrapelvic pressure and perfusion rate at varying degrees of ureteric obstruction was investigated in the rabbit ureter. There was smooth, laminar (Poiseuille) flow in the ureter over a wide range of flow rates even in the presence of sharp constrictions. The theoretical basis of these findings in terms of the fluid mechanics of collapsible tubes is defined and their importance in the assessment of equivocal upper tract obstruction discussed.