The electromyographic activity of the external and internal urethral sphincters and urinary bladder on vaginal distension and its role in preventing vaginal soiling with urine during sexual intercourse.

Objective: We investigated the hypothesis that external (EUS) and internal (IUS) urethral sphincters and urinary bladder (UB) respond to penile thrusting (PT) of vagina in a way that prevents urinary leakage during coitus.

Methods: Vaginal condom was inflated with air in increments of 50-300 ml and EMG of EUS and IUS and vaginal pressure were recorded; test was repeated after anesthetization of vagina, UB, EUS, and IUS.

Results: Vaginal distension effected reduction of vesical pressure but increase of IUS EMG until the 150 ml distension was reached, beyond which more vaginal distension caused no further effect; EUS EMG showed no response. Vaginal distension while vagina, UB, EUS, and IUS had been separately anesthetized, produced no change.

Conclusions: Vaginal balloon distension appears to effect vesical relaxation and increased IUS tone. This seems to provide a mechanism to avoid urine leakage during coitus and to occur through a reflex we term 'vagino-urethrovesical reflex'.