AIM: To investigate if the tension-free vaginal tape (TVT) works by increasing the abdominal to urethral pressure impact ratio (APIR).

METHODS: Twenty one women with urodynamically proven stress urinary incontinence (SUI) were assessed by ICIQ-SF, pad-weighing test, incontinence diary and Urethral Pressure Reflectometry (UPR) before and after TVT. UPR was conducted during resting and increased intra-abdominal pressure (P(Abd)) by straining. Related values of P(Abd) and urethral opening pressure (P(o)) were plotted into an abdomino-urethral pressuregram. Linear regression of the values was conducted, and the slope of the line was found. The slope expresses the ratio of pressure increase in the urethra compared to the pressure increase in the abdomen and was called APIR.

RESULTS: The urethral opening pressure at rest (P(o-rest)) was unchanged after TVT, while APIR increased in all women (from 0.7 to 1.4, P < 0.0001).

CONCLUSIONS: The TVT seems to strengthen the urethral closure function by increasing the APIR while P(o-rest) is unchanged regardless of the type of pre-operative dysfunction. This confirms the theory of TVT's mechanism of action being mid-urethral support.