Studies of female urethral pressure profile. Part I. The normal urethral pressure profile.

The urethral pressure profile is influenced by the degree of patient relaxation, which explains marked variations in measured pressure values among normal subjects, as well as the frequent lack of reproducibility in a given subject. The quality of relaxation can be estimated by observing the difference between maximum resting and maximum holding pressures. The most reproducible parameters are 1) the total urethral length, 2) the length to the point of maximum pressure and 3) the ratio of area to the point of maximum pressure over total area. Changes in intravesical volume do not produce significant differences in peak pressure, total area or area to maximum pressure. When subjects were asked to strain the pressure in the proximal urethra increased by 60% of the intravesical pressure observed, even in the absence of a vesical neck opening.