Detrusor contractility--order out of chaos

This paper comprises a critical assessment of the many competing ways of assessing detrusor contractility in the urodynamic clinic. It is based on measurements made in a group of elderly women, and the conclusions apply, strictly speaking, only to that population. Detrusor contractility has two aspects, which appear to be independent of each other: the strength of the detrusor contraction and whether the contraction is adequately sustained. The second of these can be assessed quite simply from postvoid residual urine. The main aim of the paper therefore is to identify and recommend one or two best methods of measuring detrusor contraction strength.

For research, the isovolumetric detrusor pressure should be measured during a continuous occlusion test or a mechanical stop test, effected by blocking the outlet with a balloon catheter. For routine clinical use, where ease of performance and minimization of repeat catheterization are important considerations, the isovolumetric detrusor pressure may be estimated from a simple contractility index PIP (=pdet.qmax + Qmax, in the usual urodynamic units). The older indices detrusor coefficient, projected isovolumetric pressure and bladder contractility index, the detrusor power and the well-known contractility nomogram, are not recommended for use in older women. Except for specialized research purposes, the Watts factor does not offer enough advantages to offset the complex calculation required. These conclusions may require modification for male patients.