Pelvic floor activity patterns: comparison of nulliparous continent and parous urinary stress incontinent women. A kinesiological EMG study.

OBJECTIVE: To introduce neurophysiological methods to search for damage to neuromuscular structures involved in sustaining continence in women who experienced stress urinary incontinence during pregnancy and/or after delivery. PATIENTS AND METHODS: Eight stress urinary incontinent parous women (mean of 2.75 vaginal deliveries [range 2-4] median age 45.3 years [range 31-60]) were examined using simultaneous electromyogram recordings of the left and right pubococcygeus muscle via wire electrodes. Comparisons were made with 10 nulliparous continent women (median age 27.2 years [range 22-32]).
RESULTS: Individual muscle activation patterns in stress urinary incontinent parous women were in principle similar to those observed in the continent nulliparous women, with two significant exceptions: (i) voluntary 'squeeze' showed significant differences in the holding time between the parous stress urinary incontinent patients and the nulliparous continent controls, with an empty bladder (49.0 s versus 193.9 s median value) and a full bladder (39.2 s versus 198.4 s); (ii) asymmetrical and uncoordinated levator activation patterns were demonstrated in four of eight parous stress incontinent women, i.e. inhibition of motor unit firing on coughing (n = 3) and dissociated recruitment of motor units during voluntary and reflex activation (n = 1).
CONCLUSION: Childbirth appeared to induce both quantitative and qualitative changes in the pelvic floor which jeopardized the continence mechanism. Sphincter weakness appeared to result not only from the loss of motor units but also from altered activation patterns in the remaining units: shorter activation periods, lack of response or paradoxical inhibition. Kinesiological EMG recordings revealed behavioural abnormalities which appeared relevant for planning treatment.