Different voiding dynamics in stable and unstable bladders with and without outlet obstruction

Of 120 men with benign prostatic enlargement who were evaluated urodynamically, 60 had stable bladders, with (n=30) and without (n=30) outlet obstruction (OO), whereas 60, both obstructed (n=30) and unobstructed (n=30), had detrusor instability (DI). The unstable bladders, wither in the absence or presence of OO, always showed a greater mechanical capability. In particular, compared to the stable bladders, the unstable ones not only had greater strength, but also showed a higher maximum shortening velocity (as well as a shorter opening time and not significantly higher internal work). In the obstructed unstable series, compared to the obstructed stable one, such findings paralleled a more severely increased urethral impedance, which suggests that a functional "compensatory" response to a greater OO was facilitated. All such data were hypothesized to result from microstructural changes yielding an easier electrical coupling between the detrusor smooth muscle cells and hence both a state of DI and better synchronized (thus, stronger and faster) micturition contractions. At least, the latter would be the case should there be no heavy bladder collagenosis upsetting the spread of the depolarization wave.