Dual simulated childbirth injuries result in slowed recovery of pudendal nerve and urethral function

Abstract

Aims: Pelvic floor muscle trauma and pudendal nerve injury have been implicated in stress urinary incontinence (SUI) development after childbirth. In this study, we investigated how combinations of these injuries affect recovery.

Methods: Sixty-seven female Sprague-Dawley rats underwent vaginal distension (VD), pudendal nerve crush (PNC), PNC and VD (PNC + VD), pudendal nerve transection (PNT), or served as unmanipulated controls. Four days, 3 weeks, or 6 weeks after injury, we simultaneously recorded pudendal nerve motor branch potentials (PNMBP), external urethral sphincter electromyography (EUS EMG), and transurethral bladder pressure under urethane anesthesia. The presence of a guarding reflex (increased frequency and amplitude of PNMBP or EUS EMG activity) during leak point pressure (LPP) testing was determined.

Results: Controls consistently demonstrated a guarding reflex. Four days after VD, EUS EMG activity was eliminated, but PNMBP activity reflected the guarding reflex; EUS EMG activity recovered after 3 weeks. Four days after PNC, both EUS EMG and PNMBP activity were eliminated, but demonstrated significant recovery at 3 weeks. Four days after PNC + VD both EUS EMG and nerve activity were eliminated, and little recovery was observed after 3 weeks with significant recovery of the guarding reflex 6 weeks after injury. Little recovery was observed at all time points after PNT. LPP results mirrored the reduction in EUS EMG activity.

Conclusion: Functional recovery occurs more slowly after PNC + VD than after either PNC or VD alone. Future work will be aimed at testing methods to facilitate neuroregeneration and recovery after this clinically relevant dual injury.

Figure 1

A. The anatomy of the pudendal nerve motor branch as seen in the neurophysiological recordings, showing the pudendal nerve (Pud. N) motor and sensory branches as well as the pudendal artery & vein. * indicates location of PNMBP recordings. B. Schematic diagram of external urethral sphincter (EUS) electromyogram (EMG), pudendal nerve motor branch potential (PNMBP), and bladder pressure recordings during leak point pressure testing. EAS = external anal sphincter.

Figure 2

Example of a leak point pressure (LPP) test with simultaneous external urethral sphincter electromyogram (EUS EMG) and pudendal nerve motor branch potential (PNMBP) recordings in a control rat at three different time scales. The two shaded bars (baseline activity and peak activity at LPP) were used to calculate increased frequency (ΔHz) and amplitude (ΔμV) in both EUS EMG and PNMBP during LPP. LPP is calculated as the baseline pressure (P baseline) subtracted from the peak pressure (P peak). +P indicates beginning of externally applied pressure to the bladder.

Figure 3

External urethral sphincter electromyogram (EUS EMG). A. Examples of baseline and peak EUS EMG activity during LPP in control (Ctr) animals, 4 days and 3 weeks (3wks) after vaginal distension (VD) and pudendal nerve crush (PNC), and 4 days, 3 weeks, and 6 weeks (6 wks) after PNC+VD and pudendal nerve transection (PNT). B. Increase in frequency (ΔHz) of EUS EMG in response to LPP. C. Increase in amplitude (ΔμV) of EUS EMG in response to LPP. Only 1 of the 5 rats studied 4 days after PNC showed an EUS EMG response to LPP testing, accounting for the high variability observed in amplitude and frequency in that group. Each bar represents mean +/- standard error of the mean of results from 5-13 rats. * indicates a significant difference (P<0.05) compared to control.

Figure 4

Pudendal nerve motor branch potential (PNMBP). A. Examples of baseline and peak PNMBP activity during LPP. in control (Ctr) animals, 4 days and 3 weeks (3wks) after vaginal distension (VD) and pudendal nerve crush (PNC), and 4 days, 3 weeks, and 6 weeks (6 wks) after PNC+VD and pudendal nerve transection (PNT). B. Increase in frequency (ΔHz) of PNMBP in response to LPP. C. Increase in amplitude (ΔμV) of PNMBP in response to LPP. Each bar represents mean +/- standard error of the mean of results from 5-13 rats. * indicates a significant difference (P<0.05) compared to control.

Figure 5

Leak point pressure (LPP) in control (Ctr) animals, 4 days and 3 weeks (3wks) after vaginal distension (VD) and pudendal nerve crush (PNC), and 4 days, 3 weeks, and 6 weeks (6 wks) after PNC+VD and pudendal nerve transection (PNT). Each bar represents mean +/- standard error of the mean of results from 5-13 rats. * indicates a significant difference (P<0.05) compared to control.