Changes in bladder contractility and compliance due to urethral obstruction: A longitudinal followup of guinea pigs

Purpose: We established the longitudinal changes in bladder contractility a nd compliance as a result of urethral obstruction using a guinea pig model. Materials and Methods: Obstruction was induced in guinea pigs by a silver r ing around the urethra. Urodynamic studies were performed longitudinally in individual animals. Bladder contractility and compliance were calculated f rom the measured bladder pressure and urine flow rate. Results: Bladder contractility developed in distinct phases. It reached a m aximum 200% increase after an average of 3.25 weeks concomitant with an alm ost 2-fold increase in urethral resistance, remained 150% to 200% increased during weeks 4 to 7 and then decreased to starting levels again, while ure thral resistance remained almost 2-fold increased. Bladder compliance decre ased by 80% during the first 3 weeks and continued to decrease to 5% of its original value after 10 to 11 weeks. Conclusions: Our data indicate that as a result of obstruction bladder func tion passes through a specific sequence of stages, including first a compen satory increase in contractility, then a stabilization phase and finally a decompensation state. In contrast bladder compliance shows a continuous dec rease. The data suggest that for assessing how far a bladder has deteriorat ed due to obstruction a combination of functional and structural data may b e warranted.