Differences between the data from free flow and intubated flow in women with urinary incontinence. What do they mean?

To assess the effects of a urethral catheter on the urodynamic data extracted from uroflow in women, and to interpret the differences from free uroflow using the VBN mathematical micturition model.

Urodynamic data of 217 consecutive (June 2002 to December 2004) women with urinary incontinence and without neurological disease or more than grade 2 prolapse were reviewed. Inclusion criteria were to perform one free flow (FF) and one intubated flow (IF) (voided volumes of at least 100 ml and continuous flow curves). Voiding parameters: volumes, maximum flow rate, detrusor pressure and flow time, were analyzed as some characteristic ratios. The VBN model was used to make simulations of various pathophysiological hypotheses.

Significant increased residual volume and flow time, decreased maximum flow rate were observed during IF. Twenty five patients had a residual volume only during IF; in that group, both decrease of Q(max) and increase of flow time were significant. Simulations showed that the geometrical effect of the catheter was not the only cause and allowed to propose the occurrence of a compression-like effect of the urethra and of a fading of the detrusor excitation after Q(max) to explain the results.

Significant differences were found between the data from a FF and an IF in women with urinary incontinence. These findings bring to the fore the impact of the transurethral catheter and underline the necessity to obtain at least one FF and one IF during a urodynamic session.