Which stop test is best? Measuring detrusor contractility in older females

Impaired detrusor contractility has an important role in geriatric voiding dysfunction but there are many competing methods of measurement. We compared the performance of 3 methods of measuring detrusor contraction strength to identify the best one.

We retrospectively analyzed urodynamics data on 84 females 53 years old or older. All had urge incontinence and were enrolled in a placebo controlled oxybutynin trial. Stop tests (voluntary interruption, mechanical interruption and continuous mechanical occlusion of flow) were performed on each subject.

At baseline the voluntary stop test measured lower mean isovolumetric detrusor pressure +/- SD than the mechanical and continuous methods (31.2 +/- 16.0 versus 47.2 +/- 26.5 and 48.7 +/- 24.4 cm. water, respectively). The latter 2 values also correlated highly (r = 0.87). Followup data on 76 women confirmed these results. Based on baseline and followup values in the 20 women who received placebo the continuous occlusion test showed highest test-retest reliability (r = 0.9, p <0.01), followed by the mechanical (r = 0.69, p = 0.01) and voluntary (r = 0.67, p <0.01) stop tests. Treatment with oxybutynin decreased isovolumetric detrusor pressure in all 3 stop tests by up to 6 cm. water. However, the decrease was statistically significant only for the continuous occlusion test.

To assess detrusor contraction strength in elderly females with urge incontinence the mechanical stop and continuous occlusion tests are acceptable but the continuous occlusion test has better reliability and better detects slight drug induced changes. Voluntary stop tests greatly underestimate detrusor isovolumetric pressure and should no longer be used.