Urethral pressure increase on effort originates from within the urethra, and continence from musculovaginal closure.

The aim of the study was to determine the contribution of intra-abdominal pressure transmission to urinary continence in the female. Five patients with genuine stress incontinence (GSI) were studied. Pressure transmission was measured in equivalent positions inside and outside the urethra and bladder during the Intravaginal Slingplasty procedure, a surgical operation used for treatment of urinary incontinence, and performed under local anaesthesia. A 6 mm diameter channel was created alongside the urethra. Two separate microtransducer catheters appropriately marked for length were inserted, one inside the urethra, and the other inside the described channel. With the vaginal hammock intact, an average of 10 simultaneous pressure measurements were made intraoperatively in response to coughing and straining in equivalent positions inside the urethra, and directly outside. Significantly higher pressure readings were found inside the urethra (P = 0.0025), indicating that an active component within the urethra may have created this pressure rise. After opening out two suburethral vaginal flaps, large quantities of urine were lost on coughing in all patients. Continence was achieved on tightening the suburethral vagina, indicating that an adequately tight vaginal hammock is a critical element in the continence process. The findings of this study question intraabdominal pressure as a mechanism contributing to continence, but support an alternative mechanism, musculovaginal closure of the urethra.