Urodynamic follow-up of experimental urethral obstruction in individual guinea pigs

It is unknown whether changes in bladder function due to urethral obstructi on follow a specific sequence. To answer this, we adapted a small animal mo del to allow repeated complete pressure-flow studies, enabling individual f ollow-up of changes in bladder function on urethral obstruction. Obstructio n was induced in guinea pigs by placing a silver ring around the urethra. U rodynamic studies were repeated under anesthesia with ketamine/xylazine. Bl adders were filled and bladder pressure measured through a single suprapubi c catheter. Urine flow rate was measured using an ultrasound probe around t he penis. Accurate measurements of bladder pressure and urine flow rates we re obtained at 1-week intervals for 11 weeks in individual guinea pigs. In the control animals, the urodynamic parameters did not show significant cha nges. In the obstructed group, urethral resistance (Plow,ave) increased fro m 20 to 35 cm H2O after 4 weeks and remained at that level. The maximum flo w rate (Q-ax) increased from 0.17 to 0.24 m.L/s after 2 to 3 weeks. After t his peak, it gradually decreased to lower than the starting value after 10 to 11 weeks. The pressure at maximum flow rate (P-Qmax) increased from 24 t o 47 cm H2O after 6 to 7 weeks and thereafter declined. During weeks 1 thro ugh 4 of obstruction, unstable contractions were seen. All animals followed a similar sequence of patterns but at variable rates. Our animal model all ows complete urodynamic follow-up of individual animals with urethral obstr uction. We observed a specific sequence of changes in urodynamic patterns a nd parameters of bladder function. Neurourol. Urodynam 20:699-713, 2001. (C ) 2001 Wiley-Liss, Inc.