A pressure-flow study was performed with a 5-micro-tip transducer cath
eter in 6 normal male volunteers (bladder neck diameters 0.80 cm. or l
arger) and 13 male subjects suspected of having bladder neck contractu
re. Intraurethral pressure was measured at various sites in the urethr
a at maximum flow to calculate hydraulic energy at these sites using t
he 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 th
e former than in the latter group. Therefore, the ''flow rate controll
ing zone'' lies at the external urethral sphincter in the former group
and at the bladder neck in the latter group.