The effect of urethral pressure variation on detrusor activity in women.

The purposes of this study were to confirm previously described patterns of urethral pressure variation and to establish criteria for their diagnosis. The effect of urethral pressure variation on detrusor activity was also examined. The study involved a retrospective review of the computerized cystometric tracings from a 26-month period. Forty-one patients had artefact-free satisfactory tracings demonstrating urethral pressure variation, detrusor instability and/or gradual detrusor pressure increase. These tracings were stored on a computer program which permitted real-time second-by-second review. Statistical analysis was done using Fisher's exact test and an independent t-test. Three patterns of urethral pressure variation were identified: rapid pressure variation (RPV), gradual pressure variation (GPV) and stress-induced transient urethral relaxation (SITUR). RPV was associated with onset at low bladder volumes (independent t-test, P = 0.02) and with detrusor instability (Fisher's exact test, P < 0.001). GPV began at high bladder volumes (Fisher's exact test, P < 0.001). SITUR was not associated with any specific pattern of urethral pressure variation or detrusor pressure change. Analysis of tracings of the patients with a combination of rapid urethral pressure variation and detrusor instability revealed a statistically significant increased frequency of urethral relaxation as the primary event precipitating an unstable detrusor contraction (Fisher's exact test, P < 0.003). In conclusion, three different patterns of urethral pressure variation were identified. Rapid pattern of urethral pressure variation is closely associated with detrusor instability. Further study of urethral pressure variation may help to elucidate the pathophysiologic mechanism responsible for idiopathic unstable detrusor contractions.