Relationship between bladder neck diameter and hydraulic energy at maximum flow.

A pressure-flow study was performed with a 5-micro-tip transducer catheter in 6 normal male volunteers (bladder neck diameters 0.80 cm. or larger) and 13 male subjects suspected of having bladder neck contracture. Intraurethral pressure was measured at various sites in the urethra at maximum flow to calculate hydraulic energy at these sites using the Bernoulli equation. When the subjects were divided into 2 groups (1 group with a bladder neck diameter of 0.73 cm. or larger and 1 with a bladder neck diameter of 0.60 cm. or smaller), the relative value of energy (ratios to the initial energy generated in the bladder) at the external urethral sphincter was significantly (p < 0.01) greater in the former than in the latter group. Therefore, the "flow rate controlling zone" lies at the external urethral sphincter in the former group and at the bladder neck in the latter group.