Validation of a water-load protocol to define the pattern of bladder sensation

The aim of this study was to confirm reliability of a water-load diuresis protocol and to assess the utility of bladder sensation curves.

For confirmation of fixed diuresis rate (phase 1), 12 volunteers consumed 250-300 ml of water every 15 min and recorded bladder sensation on a visual analogue scale (VAS) every 5 min to maximum sensation over two filling cycles: voids 1 and 2 (V1 and V2). The test was performed twice. For test-retest validation (phase 2), 24 participants underwent the same protocol drinking 300 ml of water every 15 min. Diuresis rates and voided volumes were compared between cycles and across tests.

In phase 1, there was no difference in median void volume (V1 735 ml, V2 678 ml p = 0.433) or median diuresis rates (V2 12.1 ml/min, V3 14.4 ml/min p = 0.136) between cycles. When comparing those who drank 250-300 ml/15 min, there was less variability in those drinking 300-ml aliquots, so this was standardised for later experiments; 95% upper confidence limit of variability of the diuresis rate was calculated as 4.5 ml/min. Any test with a greater difference was rejected as invalid. In phase 2, only 16 participants were analysed. There was no difference in median void volumes between tests [V1 763 ml and 820 ml (p = 0.109) and V2 788 ml and 796 ml (p = 0.266)] or in diuresis rates between test 1 (12.33 ml/min) and 2 (14.40 ml/min) (p = 0.056). Median area under the curve was similar between test 1 404.96 and test 2 418.63.

This refined protocol reliably produced stable diuresis with a water load of 300 ml/15 min, excluding those with a difference in diuresis rate > 4.5 ml/min.