840 Kang et al FIG. 6. Cystometric detrusor overactivity (DO)-related parameters during the filling phase in sham rats, rats with bladder outlet obstruction (BOO) for 1 week, and rats with BOO for 2 weeks. (A) DO frequency. (B) DO pressure. There were no significant differences in values among the groups. Results are expressed as mean±standard error of the mean. NS: not significant, Obs: obstruction group (unpaired Student’s t-test). be some changes in the voiding phase during this period, because the threshold pressure is a parameter for the func- tion of the voiding phase. These results of increased basal pressure are consistent with the findings of Levin and asso- ciates, who showed a rapid increase in bladder contractile response during the initial stage of BOO [5,6,9]. The partial BOO in animal models is known to induce hy- pertrophy of the detrusor smooth muscle to adjust for the increased power required to expel urine against the ob- struction [5,9]. Our data showed that 1 week after the first obstructing surgery, bladder capacity was not changed, possibly because of increased basal pressure and decreased compliance, despite the increased residual volume. Two weeks after the surgery, they showed increased bladder ca- pacity with increased residual volume and compliance, and their bladder weight increased both at 1 and 2 weeks after the surgery. This might be due to the change in bladder wall characteristics such as the percentage composition of the muscle and collagen components in the increased bladder weight. Continued overdistension has been demonstrated to impair the blood flow of the wall [14-17], resulting in ischemia. This condition can induce tissue damage in the bladder wall and major changes in its characteristics. Thus, the bladder at 2 weeks after the surgery seems to in- crease bladder capacity with increased compliance, al- though the bladder weight is not different from that at 1 week. The bladders from the animals with BOO would try to change their contractility required to overcome the in- creased outlet resistance during micturition. Some blad- ders show successful changes referred to as compensation, but other bladders show failure of micturition revealing in- creased residual urine, referred to as decompensation [6-8,18]. Clinically, the responses of the bladder to partial BOO, as seen with benign prostatic hyperplasia, also result in characteristic changes including the compensatory and decompensatory conditions [5]. The decompensated blad- Korean J Urol 2011;52:835-841 der refers to the condition with the impaired ability to emp- ty efficiently and completely, which seems to be very vague and without scientific criteria. Thus, we defined the decom- pensated bladder in our experiment as the bladder showing more than 20% of residual volume in awake cystometry. Applying this definition, most bladders during the earlier phase, such as 1 week after the surgery, already showed decompensatory changes, and the incidence was higher than that of 2 weeks. This suggests that in view of the re- sidual volume percentage, the rats’ bladder can undergo the decompensatory condition first, and then some blad- ders can achieve the compensatory function after over- coming the obstruction via structural modifications of the bladder wall, such as becoming enlarged and more compliant. This variable incidence of compensation and de- compensation in the bladder at some period might depend on differences in individual biochemical characteristics. It will be important to determine the major players among the biomolecules critical for this determination of these two conditions in the treatment of BPH. After the BOO, the rats showed variably different void- ing functions, characterized by increased frequency, re- sidual urine, and NVCs. The NVCs may develop as the re- sult of several factors. One is the surgical trauma of the ab- dominal or urethral surgery, but this occurrence seems to be associated with BOO, because sham animals did not show any NVC. Furthermore, in our study, the NVCs were determined as DO or abdominal straining, based on the presence of simultaneous changes on the IAP curve and IVP curve. Since 1 week after the surgery, DO was found in the rats with BOO, and there were no significant differ- ences between the 1 week and 2 week groups. CONCLUSIONS In obstructed rats, we observed changes in bladder func- tion and DO characteristics until the obstructed bladders