The overactive bladder syndrome (OAB) is typically accompanied by a reduced bladder capacity, which is reflected by a lowered mean voided volume (MVV). MVV is often used in clinical trials as an indicator of treatment effects in OAB. We have explored how well MVV and its changes upon treatment are correlated with other parameters of OAB (urgency, incontinence, frequency, nocturia, patient perception of bladder condition (PPBC), pad use) in two large cohorts assembled as part of non-observational studies.

Data from two previously reported, large, non-observational studies [1] were analyzed in which 1335 and 745 patients had been treated with 30 or 45 mg propiverine extended release for 12 weeks. Non-parametric Spearman rank tests were used to test for pair-wise correlations between MVV on the one and age, urgency, incontinence, frequency, nocturia, PPBC and pad use on the other hand. This was done for baseline values and absolute and % changes observed after 12 weeks of treatment. Data are reported as correlation coefficient r, number of patients in a given correlation analysis and the associated, descriptive p-value.

Median basal MVV in study I was 150 ml (102; 200) and increased to 200 ml (150; 250) after 4 and to 220 ml (179; 280) after 12 weeks. Median intra-individual changes were 45 ml (-25; 110) or 127% (85; 195) after 4 and 60 ml (-10; 130) or 142% (94; 208) after 12 weeks. Among the 1114 patients with data at visits 1 and 3, 733 reported an increase in MVV of >10 ml, 108 patients reported no change (defined as (≥-10 to ≤10 ml) and 273 patients had a reduced MVV by at least 10 ml. In study II, median basal MVV was 150 ml (100; 211) and increased to 200 ml (150; 250) after 4 and to 220 ml (150; 300) after 12 weeks. Median intra-individual changes were 30 ml (10; 54) or 120% (105; 667) after 4 and 50 ml (18; 90) or 132% (110; 162) after 12 weeks. Among the 620 patients with data at visits 1 and 3, 474 reported an increase in MVV, 108 patients reported no change and 38 patients had a reduced MVV.
Neither basal MVV (Table 1) nor treatment-associated changes thereof (Tables 2-3) were correlated with age. In contrast, basal MVV and treatment-associated changes were correlated with all other OAB parameters; however, those correlations were consistently weak with Spearman r being <0.4 for correlation of basal parameters and <0.5 for those with treatment-associated changes.

MVV is not correlated with age, but with severity of OAB symptoms, PPBC and pad use; moreover, changes in MVV upon treatment (regardless whether calculated as absolute or % changes) are also correlated with those of OAB symptoms, PPBC and pad use. However, all correlations were of weak to moderate strength only. Based on correlations coefficients of <0.5, MVV statistically accounted for less than 25% of the variability of other parameters.

A correlation between MVV and other OAB-related parameters is expected based on physiological principles and was confirmed in two large datasets. However, correlations had weak to moderate strength only, raising the possibility the pathophysiological factors regulating MVV may at least partly differ from those of OAB symptoms.

Amiri et al. J Clin Med 10: 311, 2021