The pressure within a collapsed tube, with special reference to urethral pressure

Dynamics of the upper urinary tract: I. Peristaltic flow through a distensible tube of limited length

A theoretical analysis and numerical solutions are presented for viscosity-dominated flow through a uniform, highly distensible tube with a slit-shaped cross section undergoing peristalsis. At flow rates below an intrinsic upper limit to the peristaltic carrying capacity of the tube, provided that there is always at least one peristaltic contraction wave in the tube, two different types of steady peristaltic flow are possible, with well defined boluses separated by regions where the tube is nearly completely occluded (flow with isolated boluses and flow with boluses in contact). Above this limit two other non-steady types of flow are possible, in which the boluses are less well defined and the contraction waves are in general not completely occlusive (flow with leaky boluses and open-tube flow). In flow with isolated boluses, boluses in contact and leaky boluses, the upstream pressure is determined by the mechanical properties (active and passive) of the tube undergoing peristalsis. In open-tube flow it is primarily determined by the resistance of the outlet from the tube.

Dynamics of the upper urinary tract: II. The effect of variations of peristaltic frequency and bladder pressure on pyeloureteral pressure/flow relations

The dynamics of pyeloureteral flow is described when there is no peristalsis and for peristalsis of high and intermediate frequencies, on the assumption that the ureter is uniform except in the mid-ureter and at the outlet. The possibility of upstream transmission of bladder pressure variations to the renal pelvis is considered. The overall behaviour depends on three principal variables, the maximum tube pressure in the contraction waves, the intrinsic peristaltic carrying capacity and the peristaltic frequency f, expressed in the form fT where T is the time for a peristaltic contraction wave to sweep through the ureter. At intermediate peristaltic frequencies (fT less than but comparable with one) oscillatory flow patterns can occur, in which periods of peristaltically driven flow alternate with extraperistaltic periods of flow through the open ureter. The kidney is better isolated from bladder pressure variations when the peristaltic frequency is high, but high peristaltic frequency can by itself lead to elevated renal pelvic pressure if the flow rate is high. Experimental observations in pigs are presented to support these conclusions.