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 chr onic bladder distension, we previously defined the zero pressure volume (ZP V), the largest contained volume at zero transmural pressure. In the curren t study, we investigated the short- and long-term effects of outlet obstruc tion and de-obstruction on chronic distension and passive bladder filling m echanics. Voiding patterns were measured 10 days (short term) or 6 weeks (l ong term) after partial bladder outlet obstruction and the bladders were te sted in vitro at that time. De-obstructed bladders were obstructed for 6 we eks, and voiding patterns were measured 10 days or 6 weeks after de-obstruc tion, followed by in vitro testing. Mean voided volume was increased in de-obstructed bladders but not obstruct ed bladders. The volume of urine in the bladder at euthanasia was greater t han mean voided volume in obstructed bladders and less than mean voided vol ume in de-obstructed bladders, indicating large residual urine in the obstr ucted bladders. ZPV was significantly increased only after long-term obstru ction or de-obstruction. Similarly, intravesical pressure and mean bladder wall stress were increased only after long-term obstruction or de-obstructi on. We conclude that tissue remodeling occurs in the bladder wall after lon g-term obstruction, possibly both as a result of and leading to chronic ove rdistension and high residual urine. Tissue remodeling occurs in the bladde r wall after long-term de-obstruction, possibly due to large voided volumes . (C) 1999 Wiley-Liss, Inc.