Spatial distribution and timing of transmitted and reflexly generated urethral pressures in healthy women.
We localized the temporal and spatial distribution of pressures in the urethra to identify their contribution to continence. With the data obtained we resolved the timing between the passively transmitted and actively generated urethral pressures. Data were obtained from 11 healthy female volunteers, with a mean age of 22 years. Simultaneous measurements of bladder and urethral pressures were taken from subjects during the Valsalva maneuver and coughing, and then holding with the subject in the supine, standing and sitting positions. The ratio of urethral to bladder pressure increase and the latency between these pressure increases were analyzed. A biphasic pressure distribution results from coughing with subjects in all positions. The first phase occurs at the normalized distance of 10 to 15 per cent from the bladder neck, where the ratio of urethral to bladder pressure increase is 0.8. The second phase occurs at 60 to 70 per cent of the urethral length and has a 1.5 to 1.7 ratio of urethral to bladder pressure increase, indicating the presence of pressure magnification. Simultaneous latency measurements indicate that the pressure increase in the urethra precedes that of the bladder by 240 plus or minus 30 msec. in the region that exhibits maximum pressure magnification. These results indicate that a fast-acting contraction occurs in the distal third of the urethra, which contributes reflexly to the compressive forces of the proximal urethra, thereby preventing urine loss during stress.