Localized contractions in the normal human bladder and in urinary urgency

To describe an observational study to establish whether localized activity arises in the normal human bladder, and whether there is any correspondence between changes in such activity and reported sensation.

The generation of sensory information by the bladder depends on afferent stimulation by increased tension within the bladder wall. Autonomous bladder activity is apparent in several species, which is often localized and multifocal, giving rise to localized areas of stretch. Thus afferent activity may partly result from localized distortions of the bladder wall. Fourteen women patients presenting with increased bladder sensation during filling-phase cystometry were compared with six asymptomatic women volunteers. Localized bladder activity was assessed by the micromotion detection (MMD) method, using eight electrodes mounted on a Silastic balloon; local displacements of the electrodes were recorded as changes in electrical resistance, which were used to compute changes in the distance between each pair of electrodes.

In two of the six volunteers, micromotions were seen in the extraperitoneal (ventral) portion of the bladder. Women with increased sensation on filling cystometry had a significantly higher prevalence of localized activity than the control group during MMD recording. The localized activity was more sustained and at a higher frequency than in asymptomatic women. All nine women reporting urinary urgency during MMD recording had localized contractile activity, while only four had phasic increases in detrusor pressure during the episodes of urgency.

By measuring localized contractions within the bladder wall, we established a significant difference in the prevalence of localized activity between the groups studied, but there was no objective difference with conventional urodynamic studies. There was also a difference in the character of the localized contractions, with the exaggerated activity in the symptomatic group corresponding with the reported sensations. These findings suggest that localized distortion of the bladder wall stimulates afferent activity, and that the human detrusor may be functionally modular.