Decompensated Bladder Following Bladder Outlet Obstruction 839 FIG. 4. The volume parameters in sham rats, rats with bladder outlet obstruction (BOO) for 1 week, and rats with BOO for 2 weeks. (A) Bladder capacity. (B) Micturition volume. (C) Residual volume. (D) Micturition interval. Results are expressed as mean±standard error of the mean. NS: not significant, Obs: obstruction group. ap＜0.05, bp＜0.01 (unpaired Student’s t-test). FIG. 5. The percentage of residual volume to bladder capacity in sham rats, rats with bladder outlet obstruction (BOO) for 1 week, and rats with BOO for 2 weeks. The rats with BOO showed significantly increased but variable values compared with the sham rats. Results are expressed as mean±standard error of the mean. NS: not significant, Obs: obstruction group. ap ＜0.05, bp＜0.01 (unpaired Student’s t-test). The dotted line indicates the criteria of decompensation as 20%. pensatory changes in the bladder have been known to come after the compensatory changes, and those are stabilized by 2 weeks after the initiation of BOO [6,8]. However, our results suggest that decompensation can come before com- pensation, which can happen before 2 weeks after BOO. Previous studies on awake animal models for partial BOO have provided clear evidence for the increased blad- der weight, bladder capacity, residual volume, compliance, and NVCs [6,7,11]. However, many earlier studies could not provide clear evidence for the parameters of pressure and DO. In most urodynamic studies with awake rats with BOO, only IVP was measured, assuming that changes in the IVP curve reflect detrusor activity. Because a charac- teristic of an awake animal is to show instinctive and un- predictable physical activity that is difficult to control, however, movement-induced changes in IAP and IVP could limit the relevance of rats as a BOO model [12,13]. Our data with IAP measurement clearly showed that 1 week after the first obstructing surgery, the rats began to show the DO and increased basal pressure by DP during the filling phase. The bladders seem to increase their basal tensions in response to the increasing intravesical urine volume due to the increased residual volume during the filling phase, although they do not respond properly during the voiding phase. Two weeks after the surgery, they showed increased basal pressure and threshold pressure by DP. There could Korean J Urol 2011;52:835-841