Relative filling of the bladder at daytime voids in healthy school children.

PURPOSE: We analyzed how healthy children use their bladder storage capacity during everyday life, and how transient changes in diuresis affect bladder filling and voiding intervals.
MATERIALS AND METHODS: Voided volumes and times were recorded during 1 or 2 24-hour periods by 206 healthy school children 7 to 15 years old. For each individual voided volumes were expressed as percentage of maximum voided volume (MVV). Mean diuresis preceding each void was estimated by dividing voided volume by voiding interval. A total of 1,098 voids were analyzed.
RESULTS: The first void in the morning was the largest for a majority of the children (73%). Most daytime voids were considerably smaller than the individual MVV. Single voids less than half MVV occurred in 80% of the children, and more than one-third had voids smaller than 20% of their storage capacity. MVV was the same for children with different voiding frequency but the relative filling decreased with the number of voids per 24 hours. At high diuresis voids tended to occur at shorter intervals with somewhat larger relative filling of the bladder. Nighttime voids that occurred in 23 children were in most cases (19) much smaller than the individual MVV.
CONCLUSIONS: Healthy children typically void when they want to, not necessarily when they need to, and only exceptionally with a full bladder. The voiding pattern is more dependent on social activities and convenience than on physiological factors such as bladder capacity, filling and diuresis.