Dynamics of micturition in benign prostatic hypertrophy patients with compensated obstruction of the vesical outlet: a denervation supersensitivity-related energy-saving mechanism.

Infravesical obstruction was assessed by pressure flow study in 40 benign prostatic hypertrophy patients with a fully compensated bladder (20 stable and 20 unstable). The degree of obstruction was defined by the minimum contraction strength needed by the detrusor to start the urinary flow (opening contraction power). There were significant positive correlations among opening contraction power, maximum flow rate and maximum external voiding power, and a negative correlation between opening contraction power and voiding duration (r = -0.54, p less than 0.001). Such features suggest a decreased electrical resistance between the detrusor smooth muscle cells (due to an obstruction-related state of denervation supersensitivity) and would mirror an energy-saving mechanism. This probably works only when there is no heavy detrusor collagenosis upsetting the depolarization wave. Within physiological muscle mechanical limits, severely obstructed bladders could thus empty completely despite even highly increased amounts of work needed per unit of volume voided.