OBJECTIVES: To evaluate bladder capacity at the time of enuresis and compare the daytime capacity of enuretics with that of controls. METHODS: The functional bladder capacity (FBC), which was the maximal endurable capacity in the daytime, the ordinary bladder capacity (OBC), which was the capacity at ordinary urinary sensation in the daytime, and the enuretic bladder capacity (EBC), which was the capacity at the time of enuresis, were measured in 67 patients with monosymptomatic nocturnal enuresis. The EBC was measured using a diaper and enuresis alarm. The FBC, OBC, and nocturnal bladder capacity, which was the maximal voided volume in the nighttime, were also measured in 67 controls. RESULTS: The FBC was not significantly different between enuretics and controls. The EBC in enuretics was significantly smaller than the nocturnal bladder capacity in controls. In enuretics, the EBC was significantly smaller than the FBC and was similar to the OBC. In controls, no statistically significant differences were found between the FBC and the nocturnal bladder capacity. CONCLUSIONS: In enuretics, the bladder capacity during sleep was significantly smaller than the daytime functional capacity. In controls, on the other hand, the bladder capacity during sleep did not differ from the daytime functional capacity. Our understanding of the bladder capacity in enuretics may need to change in view of this result. The inability to hold urine during sleep may be an important cause of nocturnal enuresis.
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