Hypothesis / aims of study
Many adult women have lower urinary tract (LUT) symptoms and dysfunction. Their incidence of bladder outflow obstruction (BOO) is however low. Underactive detrusor voiding contraction (DVC) is equally relevant in both sexes. Deterioration of the detrusor muscle contractile quality and quantity plays a role regarding to LUTS and advancing age.
An objective and graded diagnosis of the pathophysiology of (detrusor) voiding dysfunction and of underactive DVC can be useful when ineffective voiding (reduced voiding percentage (Void%) (PVR)) or prolonged voiding is present. This will become especially relevant when a specific treatment for DU is available. A second aim to quantify DVC in women however, is prediction of ability to void effectively after a (potentially somewhat) obstructing intervention for urinary incontinence. Based on current evidence it is undetermined whether one or more of the known parameters are suitable for both aims.
The quantification of detrusor contraction force in men is, based on the currently known physiology of micturition, neither overly complex nor very controversial. In women on the other hand, the micturition usually has a higher flowrate, which means a much faster detrusor muscle contraction shortening speed. Determining the detrusor force at such a high shortening speed is less straightforward and clinical cutoffs are more difficult to obtain.
Standard parameters for DVC force based on pressure flow studies (PFS) are Watts-factor (WF), and BCI, which are especially satisfactory for analysis of men. WFmax and BCI do not give significantly different results per patient in men, especially not if there is some bladder outflow obstruction. These parameters seem however less applicable and are less validated in women. Several clinical studies find a moderate association with symptoms and or ineffective micturition when using the standard parameters e.g., diagnosing DU. Some research suggests an adjustment to the BCI for women from BCI=pdetQmax+5Qmax to PIP(1)= pdetQmax+Qmax (or DECO when PIP/100 is used) to obtain a better association with stop flow testing. (1,2)
We tested in a large database which of the PFS –analysis parameters was best associated with ineffective voiding; with high PVR and low Void%, and whether or not the alternative BCI, PIP(1) is a better quantifier of detrusor voiding dysfunction in women.
Study design, materials and methods
We analyzed 1332 PFS of women with signs and symptoms of LUTD without relevant neurologic abnormalities and excluded 221 measurements of women that voided <100mL or >800mL and or had a PVR of >500mL with the PFS. Indication for UDS has been SUI-syndrome(8%) urgency/OAB syndrome(28%) (bladder/pelvic pain/recurrent UTI(31%) voiding symptoms(9%) Mixed/unspecific UI(20%) enuresis/pre-kidney transplant/other(4%).
1111 women had a mean age of 50,2y (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%) had void% 100.
Results
27 (2,4%) women had BOO and 393 (35,4%) had DU when BCI<100 is used. PVR correlated very weakly negative with age: pearson R .182 (p.000), negative with contraction; BCI: R -.318 (.000), WFmax R -.232 (.000) and weakly positive with BOOI: R .234 (.000) and URA R .210 (.000).
Figure 1 shows PFS results (PdetQmax/Qmax) of all patients in the PFS-plot: The patients with a voiding efficacy <80% are marked♦ and present mainly in the (left lower) low flow -low pressure (=DU) area. The majority of the patients in this area had effective voiding (66,1%). BOO(I >40) is rare (right side area) and especially patients with BOO and DU had (8/11) PVR. Women 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 2.1) 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 to PIP(1) (second (ROC 2.2) (dotted line) has a negative effect on predictive value for PVR. (Adapting BCI to PdetQmax + 10Qmax equals the original BCI). The effectivity of voiding of women is predominantly affected by contraction (emptying) velocity (Qmax).
Interpretation of results
Detrusor voiding contraction of women happens at higher velocity than men. Contraction velocity (flowrate) is more relevant than force (pressure) in women when compared to men.
The parameters WF, Qmax and BCI show an acceptable association with ineffective voiding in women and can be used for the diagnosis and grading of detrusor underactivity. BOO is rare in women but parameters that quantify BOO (BOOI and URA) but also associate with ineffective voiding, and are useful to exclude DU as a cause of PVR and ineffective voiding in women.
If BCI is adapted to PIP(1) and, the sum of pressure and flow thus includes less weight to the flow -value, its validity to associate with ineffective voiding reduces. If PIP(1) associates better with maximum of isovolumic contraction (stop flow -test) then PIP(1) may be a parameter that is superior in the ability to predict voiding after anti -incontinence surgery. This should be prospectively tested.
Concluding message
A large study analyzing PFS results, demonstrates that the contraction parameters Qmax, WFmax and BCI associate with ineffective voiding in women. Age and outflow obstruction are negatively associated. These contraction parameters are useful to diagnose and grade detrusor underactivity.
PIP(1) is an adaption of BCI and associates less with ineffective voiding than BCI. PIP(1) however, may be more useful (than BCI) to predict the ability to void after anti incontinence surgery but this should be prospectively tested.
Analysis of a very large set of voidings of women, with the full range of symptoms of dysfunction, has learned the relevance and validity of the diverse pressure flow study parameters. On theoretical clinical epidemiological grounds BCI and PIP(1) may have different clinical diagnostic relevance, related to the two aims of assessing detrusor voiding contraction strength in women.