Refractoriness of urethral striated sphincter during voiding: studies with afferent pudendal reflex arc stimulation in male subjects.

To assess the excitability of the striated sphincter under normal and abnormal conditions, electrostimulation of the periurethral striated sphincter via the dorsal nerve of the penis was done with the patient at rest and during voiding. Monitoring of simultaneous intravesical and intramembranous urethral pressures, and electromyographic responses of the striated sphincter was performed under fluoroscopic guidance in 14 male subjects. The urethral striated sphincter attained a state of relative refractoriness during detrusor contraction (voiding phase) and greater amounts of afferent stimulation were required to elicit sphincter contractile activity compared to the amounts required during resting states. Under conditions of a hyperactive detrusor with synergic voiding, the amounts of stimulation required to elicit striated sphincter responses were higher than those required in normal subjects. On the other hand, under conditions of striated sphincter dyssynergia, minute amounts of afferent stimulation were enough to produce sphincter contraction during voiding.