[The active forces of continence. Illustration by quantified analysis of the electromyographic signal of the urethral striated sphincter combined with urethral pressure studies].

Continence in women, ensured by a constantly positive urethral closing pressure, is the result of two phenomena: purely passive factors (urethral pressure and compliance, transmission of bladder pressure to the urethra) and active factors mediated by a voluntary and reflex neuromuscular mechanism (contraction, reflexivity, sphincter endurance). In order to define these active forces of continence, we simultaneously studied the quantitative electromyographic activity of the striated sphincter and the bulbocavernosus muscle and variations in the urethral and vesical pressure under various conditions (rest, coughing, stimulation of the pudendal nerve). During coughing, the urethral pressure peak occurred earlier (100 milliseconds) than the vesical peak, associated with hypertransmission of 20%, the bulbocavernosus muscle contracted first, followed by contraction of the striated urethral sphincter (150 ms delay) and this electrical activity preceded the rise in vesical and urethral pressures. Stimulation of the pudendal nerve eliminated the possibility of an artefact related to coughing and induced the same sequence of events.