Bladder voiding efficiency is measured according to the degree of bladder emptying and defined as the ratio between voided volume and total bladder capacity [1]. This simple index, easy to calculate, is not widely used; more, evaluation from free flow (FF) has not been reported. 
Aims of the study were first to evaluate the reproducibility of BVE between FF and intubated flow (IF) and second to search for a relationship between BVE and urodynamic diagnosis (UD) in women.

Urodynamic tracings of non-neurological women referred for investigation of various lower urinary tract symptoms were analyzed. Urodynamic study included one FF at arrival in private condition, one cystometry (filling rate 50 mL/min, triple lumen urethral catheter 7F allowing for urethral pressure recording) and one IF. Post void residual volume (PVR) was measured using a Bladder-scan. Exclusion criteria were voided volume lower than 100 mL and prolapse of grade higher than 2.

Of 226 urodynamic studies, 143 women met study criteria. Mean age was 59.0 ± 14.4 years (range [21-90]). Presenting complaint was stress urinary incontinence (28), urge incontinence (37), mixed incontinence (45), frequency (16), dysuria (7) and other (urinary tract infection, interstitial cystitis, pain (11)). 
Overall BVE IF (79.8±28.6) was significantly lower than BVE FF (90.7±15.9) (p <.0001).
Following urodynamic study, urodynamic diagnosis was posed according to the ICS/IUGA recommendations and 2 sub-groups defined according with involvement of detrusor. The first (78 women) had UD related to detrusor dysfunction (bladder outlet obstruction (BOO), detrusor hyperactivity with impaired contractility (DHIC), detrusor overactivity (DO), detrusor underactivity (DU)). The second (65 women) had UD found “normal” (N), related to urethral dysfunction (intrinsic sphincter deficiency (ISD)) or showing voiding triggered by urethral relaxation (URA). Comparison of BVE values is given in the following table:
(insert table)

There was no significant difference in BVE FF between the 2 sub-groups while BVE IF differed significantly (p =.0001).

Lower urinary tract dysfunction involving a disturbance of the detrusor (BOO, DHIC, DO and DU) leads to a significant decreased BVE during IF. UD diagnosis N or related to a dysfunction of sphincter or urethral behavior is not accompanied by a decreased BVE during IF. 
BVE is greatly dependent of PVR and PVR greatly dependent of detrusor contractility and also of nervous control. As the only change between IF and FF is the presence of a urethral catheter during IF (no significant geometrical obstruction), our findings reveal a change in nervous control in patients with dysfunction of detrusor function. 
Note that the only evaluation of BVE from FF must be regarded with caution as there is no correlation between BVE IF and BVE FF except in absence of detrusor disturbance.

BVE index is a relatively simple index to measure. In this large cohort of non-neurogenical women studied urodynamically for a variety of lower urinary tract symptoms, there is no correlation between BVE measured from a FF and BVE obtained during an IF. But, for a given patient, when a difference in BVE is observed between FF and IF, there seems that BVE is a good indicator of voiding dysfunction related to detrusor disturbance.

Abrams P. Bladder outlet obstruction index, bladder contractility index and bladder voiding efficiency: three simple indices to define bladder voiding function. BJU Int 1999; 84:14-15.