Improved Recovery from a Dual Nerve and Muscle Injury with Increased Frequency of Pudendal Nerve Stimulation
Brian Michael Balog, BS1,3; Dan Li Lin, MD2; Brett Hanzlicek, MS2; Margot Damaser, PhD1,2
1Cleveland Clinic Lerner Research Institute, Cleveland, OH; 2Louis Stokes Veteran Service Hospital, Cleveland, OH; 3University of Akron, Akron, OH
Women who leak urine due to an increase in abdominal pressure (e.g. coughing, laughing or sneezing), have stress urinary incontinence (SUI). During childbirth the pudendal nerve and external urethral sphincter (EUS) are injured causing a dual nerve & muscle injury, which results in pudendal nerve dysfunction observed 5 years after delivery and SUI. Accelerated nerve regeneration and functional recovery have been demonstrated with electrical stimulation (ES) of injured nerves. Recovery after simulated childbirth in rats is accelerated with twice weekly ES. Our hypotheses is that daily ES will improve recovery to a greater extent than less frequent stimulation.
Rats received either sham injury or pudendal nerve crush (PNC) & vaginal distention (VD) as a model of SUI. Wire electrodes were implanted in all PNC+VD animals and half the sham injured rats. One third of PNC+VD received sham stimulation (PNC+VD+SS) and all sham injury rats with electrodes received sham stimulation (SI + SS). The remaining PNC+VD rats were divided between daily ES (PNC+VD+DES) and 4 times/week ES (PNC+VD+4ES). Simulation parameters were 20Hz, 0.1ms, 0.3mA for 1 hour under isoflurane anesthesia, while 1 hour of isoflurane with no ES was utilized for sham stimulation. Stimulation occurred for 2 weeks after the injury and 2 weeks later leak point pressure (LPP) with simultaneous EUS electromyography (EUS EMG) and pudendal nerve sensory branch potential (PNSBP) were recorded. ANOVA followed by a Student Newman-Keuls post hoc test was used to determine significant differences between groups (p<0.05). Data is shown as mean ± SEM.
LPP was significantly decreased after PNC+VD + SS (19.0 ± 2.43 cm H20) and PNC+VD + DES (26.5 ± 1.96 cm H20) compared to sham injury with no implant (SI +NI; 40.6 ± 3.45 cm H20) or SI + SS groups (39.9 ± 2.31 cm H20), but LPP was not significantly decreased after PNC+VD + 4ES (39.9 ± 3.0 cm H20). EUS EMG was not significantly decreased after PNC+VD + 4ES (5.8 ± 1.92mV) compared to SI + NI (13.5 ± 3.79mV) or SI + SS (13.7 ± 3.97mV), but after PNC+VD + SS (1.5 ± 2.33mV) and PNC+VD + DES (1.2 ± 0.52mV) it was significantly decreased.
LPP and EUS EMG improved most with 4 stimulations per week, but frequency of stimulation did not influence PNSBP recovery. Daily stimulation may be too frequent and provide overstimulation and a mild re-injury.
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