Effect of intra-abdominally induced pressure on the urethral pressure profiles of healthy and incontinent bitches.

Objective: To determine whether reduced pressure transmission is of importance in the pathophysiologic mechanism of urinary incontinence in bitches.
Animals: 20 sexually intact, continent bitches and 21 spayed, incontinent bitches.
Procedure: Urethral pressure profiles before (resting) and after (stressed) insufflation of gas in the abdominal cavity were recorded in bitches under general anesthesia. Differences (stressed minus resting) were calculated for all variables. On the basis of these values, the pressure transmission ratio was determined.
Results: Resting pressure profiles of incontinent bitches indicated significantly (P < 0.05) lower maximal closure pressure (4.5 +/- 3.0 cm of H2O) than did those of continent bitches (11.2 +/- 7.2 cm of H2O). The intra-abdominal pressure increase lead to a shortening of total profile length, which was equal in both groups and caused an increase in maximal urethral pressure. The change in maximal urethral pressure was significantly (P < 0.05) greater in incontinent bitches (12.4 +/- 4.1 cm of H2O) than in continent bitches (8.8 +/- 4.5 cm of H2O). The profile areas and the pressure transmission ratios did not differ significantly (P < 0.05) between the 2 groups.
Conclusion: The effect of decreased pressure transmission on the urethra is not a factor in the pathophysiologic mechanism of urinary incontinence attributable to urethral incompetence in bitches.