Definition of detrusor contractility remains confused as that mechanical property depends partially of pressure and partially of flow. Evaluation of detrusor contractility in women remains discussed because attempts to define a contractility index have been primarily conducted in male population.
Recently 3 detrusor contractility indices, projected isovolumetric pressure (PIP-DECO-BCI) [1], projected isovolumetric pressure 1 (PIP1) [2] and k from the VBN mathematical model [3] have been compared for women referred for evaluation of various lower urinary tract symptoms (LUTS). The authors concluded that PIP1 and parameter k produced comparable and consistent results with the urodynamic diagnosis while PIP-DECO-BCI leads to inconsistencies.
The purpose of our study was to analyze detrusor contractility, using PIP1 and parameter k, in a large population of post-menopausal women referred for evaluation of various LUTS in terms of ageing, main complaint and urodynamic diagnosis. If PIP1 has been proposed for “elderly” women, parameter k is defined for anybody. An additional purpose was to search for a potential supremacy of one of these indices for evaluation of detrusor function.

Urodynamic tracings of non-neurologic post-menopausal women who were referred for investigation of various LUTS were retrospectively analyzed.
Exclusion criteria were urinary tract infection on presentation, to be unable to void and/or expelled catheter during IF, voided volume < 100 mL, pelvic organ prolapse of grade ≥ 2, diabetes mellitus. In addition, interrupted flow or voiding by abdominal straining was also excluded.
For ageing analyze chosen intervals were 65-74 years (“early elderly”) and ≥ 75 years (“late elderly”).
After urodynamic session, a urodynamic diagnosis (UD) was posed according to the ICS/IUGA recommendations. UD were bladder outlet obstruction (BOO), detrusor overactivity with impaired contractility (DHIC), detrusor overactivity (DO), detrusor underactivity (DU). Some investigations were found “normal” (N) and other related to urethral dysfunction (intrinsic sphincter deficiency (ISD) or voiding triggered by urethral relaxation (URA)).

Retrospectively 190 urodynamic tracings of non-neurologic women were analyzed. Mean age was 74.5 years [65-96 y].
Influence of age
There was no significant difference between PIP1 values (32.28±11.92 vs. 32.09±11.05) and k values (.231±.272 vs. .257±.234) with ageing. 
Influence of main complaint
Regarding main complaint for which the UDS was ordered, there was significant difference between UUI and SUI (PIP1: p = .0153; k: p = .0166) and between UUI and OTHER (PIP1: p = .0069; k: p = .0083), the value of both indices for UUI being higher.
Influence of urodynamic diagnosis
Looking at urodynamic diagnosis for the whole population PIP1 and k gave comparable results as there was significant difference between BOO vs. DHIC, DU, ISD URA and N, DHIC vs. DO and N, DO vs. DU, ISD, URA and N, DU vs.ISD and N, ISD vs. N.
With the age stratification, there was no significant difference for each urodynamic diagnosis vs. age (Figure):

Some studies have described a deteriorated detrusor function (based on urodynamic studies), a decreased contractility in post menopausal women (based on pressure-flow studies parameters) and decreased detrusor function and efficiency (based on voiding parameters and BCI) in older women with predominant SUI.
Whatever the complaint or the urodynamic diagnosis PIP1 and k have no significant difference with ageing. It has been shown in a previous study (k evaluation) that after a small decrease in younger population (“reproductive” and “peri-menopausal”) detrusor contractility reaches a low level after a sharp decrease [3]. Looking at urodynamic diagnosis there is no significant difference between the relative values of PIP1 and k whatever the diagnosis and an interesting result is the quasi absence of difference between each index with aging.
Superiority of one index is not demonstrated and can be only discussed when main complaint is analyzed.

PIP1 and k are two indices allowing an easy evaluation of detrusor contractility. The decrease of bladder function is a significant characteristic of a population of older women but there is no significant evolution of the value of indices for detrusor contractility with ageing in post menopausal women whatever the complaint or the urodynamic diagnosis. None of these indices has predominance and both can be used for evaluation of detrusor contractility.

Schäfer W. Analysis of bladder outlet function with the linearized passive urethral resistance relation, linPURR, and a disease-specific approach for grading obstruction: from complex to simple. World J Urol 1995; 13: 47–58
Tan TL, Bergmann MA, Griffiths D, Resnick NM. Stop test or pressure-flow study? Measuring detrusor contractility in older females. NAU 2004; 23: 184-9
Valentini FA, Marti BG, Nelson PP, Zimmern PE, Robain G. Usefulness of an algebraic fitting of nomograms allowing evaluation detrusor contractility in women. Prog Urol. 2017 ; 27(4): 261-6. doi: 10.1016/j.purol.2016.06.010.