The Effect of Bladder Filling Rate on the Voiding Behavior of Patients with Overactive Bladder

Many self-help guides advise patients that spreading fluid intake throughout the day can reduce overactive bladder symptoms. However, although animal studies suggest a link between a faster filling rate and increased afferent nerve firing, to our knowledge the relationship between the filling rate and bladder sensation has not been examined in humans. The aim of this study was to investigate the effect of bladder volume and the bladder filling rate on the bladder sensation and voiding patterns of patients with overactive bladder.

A control group of 40 female volunteers were recruited by open advertisement. A further 24 female patients with overactive bladder were recruited from the urology outpatient department. Each participant completed the UDI-6 (Urinary Distress Inventory, Short Form), the IIQ-7 (Incontinence Impact Questionnaire, Short Form) and a 3-day sensation related bladder diary.

The proportion of urgent voids in the control group increased with increasing voided volume and bladder filling rates (each p ≤0.001). The proportion of urgent voids in patients with overactive bladder also increased with increasing voided volume and bladder filling rates (p = 0.004 and 0.013, respectively). On regression analysis the rate of bladder filling was an independent predictor of urgent voids in patients with overactive bladder but not in the control group. Patients with overactive bladder were less tolerant of higher bladder filling rates, and experienced most grades of bladder sensation at lower voided volumes and filling rates than the control group.

The bladder filling rate appears to influence the intervoiding interval and the sensation associated with each void in patients with overactive bladder. Advising patients to lower the bladder filling rate should help reduce urinary frequency, urgency and urge incontinence.