IN-VIVO CYSTOMETRIC EVALUATION OF PROGRESSIVE BLADDER OUTLET OBSTRUCTION IN RATS

Purpose: Bladder outlet obstruction in man is a common medical disorde r that may result from benign prostatic hyperplasia, urethral strictur e disease, or congenital anomaly. The functional changes that develop in response to obstruction include detrusor instability, elevated void ing pressures, and the presence of a residual urine. The aim of this s tudy was to document the development of progressive bladder outlet obs truction over time in a rat model using conscious, in vivo urodynamics . Materials and Methods: Infravesical bladder outlet obstruction was c reated in female rats by placing a jeweler's jump ring loosely around the proximal urethra. Gradual development of outlet obstruction was fo llowed urodynamically in awake animals at 3, 7, 14, 21, and 28 days po st obstruction using a subcutaneously implanted mediport. For each gro up n = 5-8 animals. Results: Animals developed large capacity bladders with increased compliance, a high residual urine volume, and spontane ous activity. Bladder capacity increased from 0.20 + 0.02 mi. to 6.30 + 1.59 ml. at 28 days post obstruction (p <0.05). Residual volume incr eased from 0.06 + 0.01 ml. to 5.95 + 1.54 ml. (p <0.05). Percent void decreases from 72 + 3.7% in sham controls to 6.7 + 2.5% at 28 d (p <0. 05). Voiding pressure increased from 12 + 1.6 mm. Hg in sham animals t o a maximum of 42 + 6.1 mm. Hg at 21 d (p <0.05). Compliance was signi ficantly higher at 28 d when compared to all other time points. 89% of obstructed animals developed bladder instability. Conclusions: This s tudy provides clear evidence of the progressive change in bladder func tion which occurs following outlet obstruction. Implantation of a subc utaneous mediport allows in vivo recording of both the filling and voi ding phases of micturition in awake animals that have intact neural re sponses. This is a precise and easily reproducible method for producin g obstruction in a small animal which can provide a continuum of tissu e and urodynamic data that may be used to further study the pathophysi ologic changes underlying bladder outlet obstruction or other models o f bladder dysfunction.