The calculation and comparison of the Detrusor Contractility Parameter and Watts Factor

Abstract

The Detrusor Contractility Parameter (DCP) (t ), can be measured easily from the pressure flow curves of a urodynamic test. The Watts Factor at maximum urine flow, WF , can be readily calculated, but is only applicable to women. In both women and men without a high degree of bladder outlet obstruction, DCP is better associated with true detrusor contractility than any Watts Factor analysis.

Can we improve our diagnosis of impaired detrusor contractility in women? An ICI‐RS 2019 proposal

“…Lacking a formal definition, the exact meaning and utility of measurement of contractility is problematic; should “contractility” be understood as a characteristic of detrusor myocytes, the detrusor layer of the bladder, the bladder within its autonomic control system, or as a cognitive human response to the physiologic challenge of bladder filling? Limiting the focus to muscle physiology, analogies to cardiac contractility have been made . Nonetheless, the useful definition of detrusor contractility may not fully align with definitions used in other disciplines due to imprecision in those originating definitions.…”

“…The preflow isovolumetric phase of the pressure/flow study has been used to assess contractility. Derived from core cardiac studies, the idea of the use of the phase of isovolumetric contraction to evaluate detrusor contractility has been examined by Fry et al 16 Two indices are proposed: v CE 5 which is maximum rate of pressure development and t 20-80 (called detrusor contractility parameter [DCP]) 3 which is the time taken for pressure rise from 20% to 80% of its maximum value. The v CE is negatively associated with age for females (not for males), significantly associated with t 20-80 and shows weaker positive associations with Q max and BCI for females; DCP is significantly associated with WF Qmax for females and can be influenced by outflow resistance.…”

“…Limiting the focus to muscle physiology, analogies to cardiac contractility have been made. 3 Nonetheless, the useful definition of detrusor contractility may not fully align with definitions used in other disciplines due to imprecision in those originating definitions. For example, as used in cardiac physiology, the term contractility refers to an intrinsic ability of myocardium to generate force independent of any load or stretch applied.…”

“…Most clinical formulations of contractility in women estimate an hypothetical maximum isovolumetric pressure (force/area), 6,7 as a power function (Watts factor [WF]), 8,9 or contraction/shortening velocity. 3,10,11 Maximum stimulation and muscle response are assumed in these measurements. In addition, the impact of altered thermodynamic efficiency, substrate availability, and metabolite clearance with aging and disease have not yet been included in clinical considerations of contractility.…”

Fundamental aspects of isovolumetric contractility measurements of urinary bladder

“…and to the x-axis (v CE =0) is used as contractility parameter v CEmax and maximum isovolumetric pressure p o respectively. Without foundation of their interpretation, the obtained fi tted plot of (dp/dt) /p versus p is taken to be similar with velocity-force relation according to (1) [13]. The course of increasing pressure between 20%-80% of maxi mum of recorded detrusor pressure is used to fi t the hyperbolic function needed for extrapolation.…”