Factors affecting detrusor contraction strength during voiding in women

To compare voiding mechanisms in continent and stress incontinent women and to assess the effects of aging, childbirth, menopausal status, and anterior vaginal wall relaxation on detrusor contraction strength during voiding.

Thirty-eight asymptomatic female volunteers underwent a thorough evaluation including multichannel urodynamic testing and instrumented pressure-flow voiding studies. The voiding mechanisms and detrusor contraction strengths, available in 30 women, were compared with those of 70 women evaluated previously with objective evidence of genuine stress urinary incontinence. The effect of age, parity, bladder neck mobility, and anterior vaginal wall relaxation on maximum detrusor pressure was assessed using chi2 and linear regression analyses. Detrusor pressures in premenopausal and postmenopausal women and continent and stress incontinent women were also compared.

Four types of voiding mechanisms were identified. All 30 of the continent women voided with a detrusor contraction, compared with 59 (84%) of genuine stress incontinent subjects. The mean +/- standard 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 subjects, maximum detrusor pressure did not correlate significantly with increasing age, parity, bladder neck mobility, or degree of anterior vaginal wall relaxation. Premenopausal women had significantly higher mean (+/- SD) maximum detrusor pressures than postmenopausal women (16.3 +/- 13.0 cm H2O compared with 11.5 +/- 11.0 cm H2O; P < .01).

Women with genuine stress urinary incontinence may be more likely to void with a weak or absent detrusor contraction than continent women. Menopausal status was the only factor identified that significantly affected maximum detrusor pressure during voiding.