Persistently increased voiding frequency despite relief of bladder outlet obstruction

Purpose: Bladder outlet obstruction (BOO) can increase urinary frequency. E ven after surgical relief of obstruction, up to 30% of patient are still bo thered by irritative voiding symptoms. We tested the hypothesis that deliga tion of a partial bladder outlet obstruction model mimics this clinical obs ervation. Materials and Methods: Female Wistar rats were obstructed for 3 weeks by pa rtial urethral ligation and then were relieved of obstruction by urethral d eligation. Measurements of voiding frequency and voided volumes were measur ed preoperatively, after ligation, and after deligation. Relief of obstruct ion was confirmed by measuring flow rates through ex vivo perfusion of deli gated urethras. Urine osmolality and bladder weights were determined. Awake cystometrograms (CMGs) were performed 3 weeks after deligation to measure bladder function. Results: Neither sham ligation nor sham deligation altered voiding frequenc y. Ligation doubled mean voiding frequency (in cc:) from 2.01 +/- 0.32 to 3 .96 +/- 0.22 per 4 hours (p = 0.0002). Three weeks after deligation, voidin g behavior of the animals segregated into 2 groups: 20% had persistent hype ractive voiding frequency (6.67 +/- 1.23 per 4 hours) while 80% normalized voiding frequency (1.53 +/- 0.20 per 4 hours). The difference in voiding fr equency in these 2 groups could not be attributed to alterations in urine o smolality, persistence of urethral obstruction, difference in bladder weigh ts or severity of initial obstruction created. Awake CMGs revealed a higher peak micturition pressure and lower voided volume in the hyperactive voide rs. Conclusions: 20% of the animals after urethral deligation had persistent hy peractive voiding which parallels clinical observations. Because the CMG da ta suggested persistent obstruction, yet urethral perfusion and bladder wei ghts indicated no obstruction, we propose that these 20% of animals have a "functional" bladder outlet obstruction sind can be used to study mechanism s underlying hyperactive voiding.