The urethral closure function in continent and stress urinary incontinent women assessed by urethral pressure reflectometry.Dan Med J. 2014 Feb; 61(2):B4795.DM
Stress urinary incontinence (SUI) occurs when the bladder pressure exceeds the urethral pressure in connection with physical effort or exertion or when sneezing or coughing and depends both on the strength of the urethral closure function and the abdominal pressure to which it is subjected. The urethral closure function in continent women and the dysfunction causing SUI are not known in details. The currently accepted view is based on the concept of a sphincteric unit and a support system. Our incomplete knowledge relates to the complexity of the closure apparatus and to inadequate assessment methods which so far have not provided robust urodynamic diagnostic tools, severity measures, or parameters to assess outcome after intervention. Urethral Pressure Reflectometry (UPR) is a novel method that measures the urethral pressure and cross-sectional area (by use of sound waves) simultaneously. The technique involves insertion of only a small, light and flexible polyurethane bag in the urethra and therefore avoids the common artifacts encountered with conventional methods. The UPR parameters can be obtained at a specific site of the urethra, e.g. the high pressure zone, and during various circumstances, i.e. resting and squeezing. During the study period, we advanced the UPR technique to enable faster measurement (within 7 seconds by the continuous technique) which allowed assessment during increased intra-abdominal pressure induced by physical straining. We investigated the urethral closure function in continent and SUI women during resting and straining by the "fast" UPR technique. Thereby new promising urethral parameters were provided that allowed characterization of the closure function based on the permanent closure forces (primarily generated by the sphincteric unit, measured by the Po-rest) and the adjunctive closure forces (primarily generated by the support system, measured by the abdominal to urethral pressure impact ratio (APIR)). The new parameters enabled a more detailed description of the efficiency of the closure function and the extent and nature of a possible dysfunction in the individual woman. The urethral closure equation (UCE) and urethral opening pressure at an abdominal pressure of 50 cm H2O (Po-Abd 50), respectively, which combine the permanent and the adjunctive closure forces, could separate continent and SUI women and thus appear to be excellent diagnostic tests. Moreover, the parameters showed highly significant negative correlation with ICIQ-SF, pad test and the number of incontinence episodes per week and are therefore valid as urodynamic severity measures. UPR in SUI women before and after TVT demonstrated a more efficient urethral closure function after the operation. The Po-rest was unchanged suggesting that the sphincteric unit was virtually unaltered and hence the permanent closure forces unchanged. However, the resting opening elastance increased by 18% indicating that at the resting state the TVT somewhat improves the closure function by providing increased resistance against the dilation of the urethra, which probably explains the decreased maximum urine flow rate found after TVT in this and previous studies. The APIR increased in all patients after TVT suggesting that the support system was re-established and thus the adjunctive closure forces improved, regardless of the type of pre-operative dysfunction. The new UPR parameters may be used as outcome measures after treatment.