Pelvic floor stress response: reflex contraction with pressure transmission to the urethra

There is still controversy regarding the active role of striated intramural and periurethral muscles and their relative share of function for urinary continence under stress conditions. To evaluate the function of the periurethral muscles, we subjected a dog model to the physiologic stress condition created by sneezing. Simultaneous measurements of intravesical and three urethral pressures were obtained in the intact urinary tract and in a noncontractile substitute urethra, which was pulled through the pelvic floor and studied with and without additional pelvic floor suspension. The data clearly confirm the active role of striated sphincteric muscles for continence under stress conditions. The reflex contraction of the striated sphincteric muscles constitutes the majority of the distal urethral closure mechanism under stress conditions and generates intraurethral pressures, which exceed those of passive transmission of intra-abdominal pressure. The intramural striated sphincter contributes a share of less than 10% to this stress response, while the vast majority of the pressure rise is generated by the periurethral striated muscles. Surgical suspension of the pelvic floor can enhance effectivity of this stress mechanism, and thus seems to be a sound physiological concept in surgical treatment of incontinence.