Volume threshold for micturition. Influence of filling rate on sensory and motor bladder function

Filling at physiological rates (natural filling) is the specific stimulus for activation of the micturition reflex. In urodynamic studies this has rarely been taken into consideration. In the vast majority of clinical urodynamic studies 50 ml/min has been the preferred filling rate. A comparative study in 17 healthy volunteers of cystometry at 50 and 100 ml/min (CMG) and ambulatory monitoring (AM) during natural filling has been performed by other authors (3). It was found that CMG increases volume threshold for micturition, impairs detrusor contractility and has lower sensitivity for detecting spontaneous phasic detrusor activity. These results are discussed in the present article. The nearest explanation is at the cellular level. Filling rates above physiological range (>15 HD (Hour-Diuresis units)) are a mechanical trauma to receptors, nerve endings, cells and cell junctions, which are temporarily functionally disturbed.