Effects of Acute Sacral Neuromodulation at Different Pulse Widths on Bladder Overactivity in Pigs

PURPOSE: Sacral nerve stimulation has been used to treat overactive bladder. This study evaluated the effects of stimulation using different pulse widths on the inhibition of bladder overactivity by sacral nerve stimulation (SNM) in pigs. METHODS: Implant-driven stimulators were used to stimulate the S3 spinal nerve in 7 pigs. Cystometry was performed by infusing normal saline (NS) or acetic acid (AA). SNM at pulse widths of 64 μsec to 624 μsec was conducted at the intensity threshold at which observable perianal and/or tail movement was induced. Multiple cystometrograms were performed to determine the effects of different pulse widths on the micturition reflex. RESULTS: AA-induced bladder overactivity reduced the bladder capacity to 46.9%±7.1% of the NS control level (P<0.05). During AA infusion, SNM at 64 μsec, 204 μsec, and 624 μsec increased the bladder capacity to 126.1%±6.9%, 129.5%±7.3%, and 140.1%±7.6% of the AA control level (P<0.05). No significant differences were found among the results obtained using pulse widths of 64 μsec, 204 μsec, and 624 μsec (P>0.05). The actual intensity threshold varied from 0.7 to 8 V. The mean intensity threshold (T visual) for pulse widths of 64 μs, 204 μs, and 624 μs were 5.64±0.76 V, 3.11±0.48 V, and 2.52±0.49 V. T visual for pulse widths of 64 μsec was larger than the other two T visual for pulse widths of 204 μsec and 624 μsec (P<0.05). No significant differences were found among the T visual for pulse widths of 204 μsec and 624 μsec (P>0.05). CONCLUSIONS: This study indicated that different pulse widths could play a role in inhibiting bladder overactivity. It is not yet certain which pulse widths increased bladder capacity compared with AA levels, to minimize energy consumption and maintain patient comfort during stimulation, 204 μsec may be an appropriate pulse width for SNM.