A NON-INVASIVE UROFLOWMETRY-BASED NOMOGRAM FOR ASSESSING THE RISK OF VOIDING DYSFUNCTION AFTER MID-URETHRAL SLING.

Valentini F1, Zimmern P2, Nelson P3

Research Type

Pure and Applied Science / Translational

Abstract Category

Female Lower Urinary Tract Symptoms (LUTS) / Voiding Dysfunction

Abstract 314
ePoster 5
Scientific Open Discussion Session 21
On-Demand
Mathematical or statistical modelling Female Bladder Outlet Obstruction
1. Rothschild Hospital, Paris, France, 2. UTSouthwestern Medical School, 3. Hopital Rothschild
Presenter
F

Francoise Valentini

Links

Abstract

Hypothesis / aims of study
Since many years mid-urethral sling (MUS) placement has become the treatment of choice for stress urinary incontinence (SUI). Following a MUS placement, urethral distortion and kinking have been observed, resulting potentially in a reduced effective cross-section of the urethra which can induce voiding dysfunction and a state of chronic outlet obstruction; that situation is not an uncommon complication.  We used the VBN mathematical model [1] to develop an algorithm based on a non-invasive flow (NIF) which could be used post-MUS to gauge the risk of such an obstructive situation developing over time.
Study design, materials and methods
In the VBN micturition model, the detrusor contractility is characterized by the parameter k and the urethral obstruction by the parameter U. The standard model (flow-controlling zone at meatus) was modified to simulate a narrowing due to a urethral compression at 1.5 cm of the bladder neck. Data derived from NIF are: filling volume (Vini) = voided volume + post void residual (PVR, obtained by bladder scan) and maximum flow (Qmax). In the absence of intubated pressure-flow recordings, values of k and U cannot be precisely evaluated. But one infinity of couples [k,U] can restore Qmax which value is a compromise between k and U; a given Qmax needs high values of k and U or low values of the parameters. To restore PVR, introduction of a fading of detrusor excitation is needed. In previous study we have shown that,in most voidings, such condition occurs after the Qmax [2]. We have to identify the value kmin of k giving the lower possible value of U which is 0; kmin will be the characteristic identifier for each woman. Therefore, an increase of kmin would imply an increase of U, thus suggesting an element of sling obstruction.
Results
Direct evaluation of kmin was easy obtained using the VBN software but this method was time consuming. Tabulation of kmin for regularly spaced values of Vini and Qmax allowed to build a 3D nomogram described by simple equations solved using Excel. Error with the VBN model was minimal (< 2%) except for cases with concomitant Vini  ≤ 100 mL and Qmax ≥ 35 mL/s.
To use the software (Figure), entries are with successive shifts: Urinated volume, then Residual Volume and then Qmax. A last shift gives kmin. If the value of kmin increases compared to the previous evaluation, the risk of voiding dysfunction is increasing.
The software and a detailed user manual are available on request from the authors for testing
Interpretation of results
Today, evaluation and diagnosis of bladder outlet obstruction rely upon flow test and PVR without any quantification. In addition one can observe variable presentation: urgency, straining to void, weak urinary stream, dysuria, urinary tract infection and so on. Invasive investigation is frequently proposed. Our method has the great merit to be non-invasive. Computations have been tested on a small sample, unfortunately non significant. We had been able to evaluate k and kmin for each woman without encountering any unexpected difficulty. This would mean that the theory is reliable. But this conclusion would be credible only if the method will be applied to a large population.
Concluding message
This unique mathematical modeling now allows the follow-up of women after MUS to detect the possible onset of outflow obstruction.
The unique patient identifier kmin is defined without ambiguity from an initial NIF and can be tracked over time with repeat NIF at each follow-up clinic visit. 
The software developed in Excel can be easily used by all practitioners.
Figure 1 Excel presentation of the model
References
  1. A mathematical micturition model to restore simple flow recordings in healthy and symptomatic individuals and enhance uroflow interpretation. F.A.VALENTINI, G.R.BESSON, P.P.NELSON et P.E.ZIMMERN. Neurourol. Urodyn. 2000; 19(2) 153-176.
  2. Can modeled analysis of urodynamic recordings help to demonstrate the nervous control of the bladder and urethra during micturition? Françoise A. Valentini, Leonor Mazieres, Pierre P. Nelson. UroToday International Journal 2010 vol 3(4) August.
Disclosures
Funding None Clinical Trial No Subjects None
27/03/2024 23:59:03