Racial differences in the structure and function of the stress urinary continence mechanism

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Abstract
Objective: To compare the structure and function of the urethral sphincter and the urethral support in nulliparous black and white women. Methods: Eighteen black women (mean age 28.1 years) and 17 white women (mean age 31.3 years) completed this cross-sectional study. The following assessments were made: urethral function using multichannel cystometrics and urethral pressure profilometry, pelvic muscle strength using an instrumented speculum, urethral mobility using the cotton-swab test and perineal ultrasound, and pelvic muscle bulk using magnetic resonance imaging. Results: Black women demonstrated a 29% higher average urethral closure pressure during a maximum pelvic muscle contraction (154 cm H2O versus 119 cm H2O in the white subjects; P = .008). Although not statistically significant, black women had a 14% higher maximum urethral closure pressure at rest (108 cm H2O versus 95 cm H2O; P = .23) and a 21% larger urethral volume (4818 mm3 versus 3977 mm3; P = .06). In addition, there was a 36% greater vesical neck mobility measured with the cotton-swab test (blacks 49° versus whites 36°; P = .02) and a 42% difference in ultrasonically measured vesical neck mobility during a maximum Valsalva effort (blacks = −17 mm versus whites −12 mm; P = .08). Conclusion: Functional and morphologic differences exist in the urethral sphincteric and support system of nulliparous black and white women.