Mechanisms of urinary continence: an animal model to study urethral responses to stress conditions

Under conditions of stress, the urethral sphincteric mechanism has to compensate a passive bladder pressure rise induced by increase in intraabdominal pressure. To evaluate the various closure mechanisms contributing to urethral response to stress, we subjected a female dog model to the physiologic stress condition triggered by sneezing. Vesical, rectal and 4 urethral pressures during sneezing were recorded simultaneously under various experimental situations: in the intact animal, after transection of the bladder and urethra, and with the abdomen open. The effects of the Credé maneuver and of manual squeezing of the surgically exposed bladder were also recorded. The data obtained support the existence of a 2-component urethral closure mechanism under stress: the proximal closure mechanism of the smooth muscular, intrapelvic urethra is from passive transmission of abdominal pressure. It is apt to balance a passive increase in bladder pressure and thus maintain proximal closure pressure during stress. The distal closure pressure mechanism reflects active reflex contraction of the intrinsic external sphincter and pelvic floor muscles, which is capable of exceeding passive increase in bladder pressure and thus augments closure pressure during stress.