Electrophysiological function during voiding after simulated childbirth injuries

During vaginal delivery dual injuries of the pudendal nerve and the external urethral sphincter (EUS), along with other injuries, are correlated with later development of stress urinary incontinence. It is not known how combinations of these injuries affect neuromuscular recovery of the micturition reflex. We investigated the EUS electromyogram (EMG) and the pudendal nerve motor branch potentials (PNMBP) during voiding 4 days, 3 weeks or 6 weeks after injury; including vaginal distension (VD), pudendal nerve crush (PNC), both PNC and VD (PNC+VD), and pudendal nerve transection (PNT); and in controls. Pudendal nerve and urethral specimens were excised and studied histologically. No bursting activity was recorded in the EUS EMG during voiding 4 days after all injuries, as well as 3 weeks after PNC+VD. Bursting activity demonstrated recovery 3 weeks after either VD or PNC and 6 weeks after PNC+VD, but the recovered intraburst frequency remained significantly decreased compared to controls. Bursting results of PNMBP were similar to the EMG, except bursting in PNMBP 4 days after VD and the recovered intraburst frequency was significantly increased compared to controls after PNC and PNC+VD. After PNT, neither the EUS nor the pudendal nerve recovered by 6 weeks after injury. Our findings indicate bursting discharge during voiding recovers more slowly after PNC+VD than after either PNC or VD alone. This was confirmed histologically in the urethra and the pudendal nerve and may explain why pudendal nerve dysfunction has been observed years after vaginal delivery.