Faster bladder filling in rats reduces detrusor overactivity but worsens (i.e., decreases) bladder compliance.

Abstract

The impact of bladder filling rate on cystometric outcomes remains unclear. Clinically, faster bladder filling is believed to increase the likelihood of observing detrusor overactivity (DO) in those with bladder dysfunction, although evidence of this is lacking. We executed this study to clarify how changes in bladder filling rate impacted cystometric parameters. Urethane anesthetized female CD rats (n = 19) underwent bladder filling at five different fill rates, a baseline rate scaled to have a filling phase of approximately seven minutes (in line with our previous work), and scaled rates of 1/3x, 2x, 4x, and 8x that speed. Contrary to expectations, filling at faster rates decreased the likelihood of observing detrusor overactivity, with 4x and 8x filling rates demonstrating less detrusor overactivity than the baseline (1x) rate (P = 0.0091 for 4x and P = 0.019 for 8x). However, faster filling rates did decrease bladder compliance. Filling at 4x and 8x demonstrated decreased bladder compliance compared to 1x (P = 0.032 for 4x and P < 0.0001 for 8x). Finally, increasing the filling rate led to increases in bladder capacity at 4x (P = 0.034) and 8x (P = 0.0066) relative to 1x. These results suggest that contrary to expectations, faster filling may not be more effective at eliciting detrusor overactivity (i.e., not a better diagnostic approach). As reductions in detrusor overactivity and increases in bladder capacity are critical parameters for evaluating preclinical therapeutics, faster filling may impair the ability to demonstrate further improvements.