The mechanics of urine transport in the upper urinary tract: 2. The discharge of the bolus into the bladder and dynamics at high rates of flow

On the basis of simple theoretical arguments and experimental results, it is shown that the discharge of the bolus into the bladder is determined by the resistance to flow of the ureterovesical junction (UVJ), which itself depends on the detrusor pressure. If the resistance to flow or the detrusor pressure are too high, or if the ureter is too wide or too weakly contracting, then the UVJ behaves as if obstructive, and bolus flow breaks down. At sufficiently high flow rates the UVJ, even though not obstructive, always governs the flow dynamics, open‐tube flow occurring instead of the isolated bolus flow characteristic of low flow rates. At intermediate rates two other flow regimes can occur: touching or box‐shaped boluses, and leaky bolus flow. In each regime the pelvic pressure varies with mean urine flow rate in a characteristic way.