Filling mechanics of obstructed and de-obstructed rat urinary bladders

Chronic bladder distension occurs after partial outlet obstruction and can lead to decompensation and impaired function. To quantify the degree of chronic bladder distension, we previously defined the zero pressure volume (ZPV), the largest contained volume at zero transmural pressure. In the current study, we investigated the short- and long-term effects of outlet obstruction and de-obstruction on chronic distension and passive bladder filling mechanics. Voiding patterns were measured 10 days (short term) or 6 weeks (long term) after partial bladder outlet obstruction and the bladders were tested in vitro at that time. De-obstructed bladders were obstructed for 6 weeks, and voiding patterns were measured 10 days or 6 weeks after de-obstruction, followed by in vitro testing. Mean voided volume was increased in de-obstructed bladders but not obstructed bladders. The volume of urine in the bladder at euthanasia was greater than mean voided volume in obstructed bladders and less than mean voided volume in de-obstructed bladders, indicating large residual urine in the obstructed bladders. ZPV was significantly increased only after long-term obstruction or de-obstruction. Similarly, intravesical pressure and mean bladder wall stress were increased only after long-term obstruction or de-obstruction. We conclude that tissue remodeling occurs in the bladder wall after long-term obstruction, possibly both as a result of and leading to chronic overdistension and high residual urine. Tissue remodeling occurs in the bladder wall after long-term de-obstruction, possibly due to large voided volumes. Neurourol. Urodynam. 18:659-671, 1999.