Although many adult women have lower urinary tract (LUT) symptoms and dysfunction, the specific incidence of voiding disorders in women is relatively low, especially when compared to LUT dysfunction in men. Clearly, when the higher age cohorts are considered, bladder outflow obstruction (BOO) plays a significantly greater role in men in association with BPH. Nevertheless, underactive detrusor contraction (DU) and likely deterioration of the contractile quality (and quantity) of the detrusor muscle play a role in both sexes. Although ineffective or prolonged voiding in women is less common, an objective and correct diagnosis of the pathophysiology of (detrusor) dysfunction is useful in many cases, especially in secondary care.
The quantification of detrusor contraction force in men is, based on the currently known physiology of micturition, neither very complex nor very controversial. In women, the micturition usually has a higher outflow rate, which means a much faster detrusor contraction (muscle shortening speed). Determining the detrusor force at such a high contraction speed is less straightforward and does not lead to clinical results so unambiguously. Standard parameters for detrusor contraction force on the basis of pressure flow studies are Watts factor, and BCI, which are especially satisfactory for analysis of men. Watts factor (maximum) and BCI do not differ in a clinically significant way in men especially not if there is some bladder outflow obstruction. These parameters seem however less applicable and are less validated in women, several researchers find a moderate association with symptoms and or ineffective micturition when using the standard parameters. Some research suggests an adjustment to the BCI for women. Especially also a change from BCI= pdetQmax +5Qmax to BCI= pdetQmax + Qmax (also labelled as PIP (or DECO when PIP/100)) is suggested to better associate with stop flow testing. (https://doi.org/10.1002/nau.20020 and or 10.1016/j.purol.2019.11.004). We tested whether pressure flow study (PFS) –analysis parameters associated with ineffective voiding; high PVR and low Void%, and whether the alternative BCI is a better predictor of voiding dysfunction in women.

We analyzed 1332 PFS of female patients with signs and symptoms of LUT dysfunction without relevant neurologic abnormalities and excluded 221 measurements of women that voided <100mL or >800mL and or had a PVR of >500mL during pressure flow study. Indication for UDS has been SUI-syndrome (8%) urgency&OAB syndrome (28%) (bladder & pelvic pain & rUWI (31%) voiding symptoms (9%) Mixed or unspecific UI (20%) enuresis /pretransplant/other (4%).
1111 women had a mean age of 50,2y (range 16-91) and voided 363mL (101-782mL) with PVR 41mL (0-492mL). Mean Qmax was 19,9mL/s (2,5-71,7mL/s) with a mean PdetQmax of 26,3cmH2O (-9,1-92,5). PVR result was very skewed with a median of 0mL; 729 (66%) voided without PVR.

27 (2,4%) women had BOO and 393 (35,4%) had DU when the standard BCI is used. PVR correlated very weakly with age pearsonR .182 (p.000) negatively with contraction; BCI: R -.318 (.000) Wmax R -.232 (.000) and weakly with outflow resistance; BOOI: .234 (.000) and URA R .210 (.000). The figure (1) shows PFS results of all patients:

The patients with a voiding efficacy <80% are marked♦ and present mainly in the (left lower) low flow low pressure (detrusor underactivity) area, although the majority of the patients in this area had effective voiding (66,1%). BOO(I >40) is rare (right lower area) and especially patients with BOO and DU had (8/11) PVR. Female with ineffective voiding were older (55,5y vs 47,8y p.000) voided less; 279mL vs 381mL (p.000) and had lower Qmax 13,6 vs 21,4mL/s (p.000).
The ROC Curve analysis (fig 2a) shows that Wmax, Qmax and BCI (left upper corner) are superior to predict effective micturition and outflow resistance parameters have a slightly less (and negative predicting value towards PVR. Adapting BCI PdetQmax +Qmax (second ROC fig 2b) (dotted line) has a negative effect on predictive value for PVR. (Adapting BCI to PdetQmax + 10Qmax equals the original BCI). The effectivity of female voiding is predominantly affected by contraction (emptying) velocity (Qmax).

This data shows clinical epidemiology of female voiding in a large cohort. Detrusor underactivity is prevalent (35% in our cohort), 66% of women are voiding without PVR. Nevertheless contraction parameters that include flowrate; WF and BCI show a god association with ineffective voiding. However e.g. to predict voiding after (slightly) obstructing interventions, commonly in use to treat stress urinary incontinence (e.g. TVT(O)) parameters that include more weight to pressure (and force of contraction) other incices may be more valuable. Bladder outflow obstruction is rare in women

Adapting PFS contractility parameters towards maximum of contraction force (including less weight for velocity (≈flowrate)) is not helpful. Although many women with detrusor underactivity have an effective micturition, female voiding effectivity depends on velocity of contraction.