FACTORS AFFECTING DETRUSOR CONTRACTION STRENGTH DURING VOIDING IN WOMEN

Objective: To compare voiding mechanisms in continent and stress incon tinent women and to assess the effects of aging, childbirth, menopausa l status, and anterior vaginal wall relaxation on detrusor contraction strength during voiding. Methods: Thirty-eight asymptomatic female vo lunteers underwent a thorough evaluation including multichannel urodyn amic testing and instrumented pressure-flow voiding studies. The voidi ng mechanisms and detrusor contraction strengths, available in 30 wome n, were compared with those of 70 women evaluated previously with obje ctive evidence of genuine stress urinary incontinence. The effect of a ge, parity, bladder neck mobility, and anterior vaginal wall relaxatio n on maximum detrusor pressure was assessed using chi(2) and linear re gression analyses. Detrusor pressures in premenopausal and postmenopau sal women and continent and stress incontinent women were also compare d. Results: Four types of voiding mechanisms were identified. All 30 o f the continent women voided with a detrusor contraction, compared wit h 59 (84%) of genuine stress incontinent subjects. The mean +/- standa rd deviation [SD]) detrusor contraction was significantly stronger in continent women than incontinent women (20.3 +/- 14.2 cm H2O compared with 12.3 +/- 11.0 cm H2O; P < .01). In continent and incontinent subj ects, maximum detrusor pressure did not correlate significantly with i ncreasing age, parity, bladder neck mobility, or degree of anterior va ginal wall relaxation. Premenopausal women had significantly higher me an (+/- SD) maximum detrusor pressures than postmenopausal women (16.3 +/- 13.0 cm H2O compared with 11.5 +/- 11.0 cm H2O; P < .01). Conclus ion: Women with genuine stress urinary incontinence may be more likely to void with a weak or absent detrusor contraction than continent wom en. Menopausal status was the only factor identified that significantl y affected maximum detrusor pressure during voiding. (C) 1997 by The A merican College of Obstetricians and Gynecologists.