Circadian variation of voided volume in normal school-age children

Area of Science:

• Pediatrics
• Urology
• Physiology

Background:

• Functional bladder capacity (FBC) and urine output are key metrics for managing pediatric incontinence and nocturnal enuresis.
• Current clinical use is limited by the absence of age-specific FBC reference ranges and arbitrary urine output measurement periods.

Purpose of the Study:

• To establish reliable reference ranges for FBC and urine output in children aged 6-12 years.
• To investigate the relationship between voided volume, urine output rate, and circadian rhythms.
• To identify factors influencing early morning voidings (EMV).

Main Methods:

• Utilized 72-hour frequency-volume charts for 54 children (6-12 years) to record voiding volume, timing, and collect samples.
• Analyzed urine samples for osmolality and creatinine concentration.
• Plotted voided volumes against urine output rates and analyzed hourly population averages of output rates.

Main Results:

• Identified early morning voidings (EMV) as significantly larger than other voidings, with maximum voided volume (MVV) often being an EMV.
• Established MVV as a reliable measure for FBC, aligning with published cystographic bladder capacity percentiles.
• Demonstrated that low urine output rates (<50 ml/h) during rest phases result in larger voidings (EMV) compared to activity phases.
• Revealed distinct circadian patterns in urine output and bladder contractility inhibition, masked by traditional block-time measurements.

Conclusions:

• The study provides crucial reference data for FBC and urine output in children, addressing previous clinical limitations.
• Early morning voidings represent maximum bladder capacity and are influenced by circadian rhythms.
• Hourly analysis of urine output reveals underlying circadian rhythms vital for understanding pediatric voiding disorders like nocturnal enuresis.