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

Abstract

Purpose: We investigated the effects of different stimulation frequencies on the inhibition of bladder overactivity by sacral neuromodulation (SNM) in pigs.

Methods: Implant-driven stimulators were used to stimulate the S3 spinal nerve in 13 pigs. Cystometry was performed by infusing normal saline (NS) or acetic acid (AA). SNM (pulse width, 210 µsec) at frequencies ranging from 5 to 50 Hz 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 frequencies on the micturition reflex.

Results: AA-induced bladder overactivity significantly reduced the bladder capacity (BC) to 34.4%±4.7% of the NS control level (354.4±35.9 mL) (P<0.05). During AA infusion, SNM at 5 Hz did not significantly change the BC (48.1%±6.9% of the NS control level) (P>0.05), but SNM at 15, 30, and 50 Hz significantly increased the BC to 54.5%±7.1%, 55.2%±6.5%, and 57.2%±6.1% of the NS control level (P<0.05), respectively. No significant differences were found among the results obtained using frequencies of 15, 30, and 50 Hz (P>0.05).

Conclusions: This study demonstrated that 15 Hz was an appropriate frequency for SNM and that frequencies higher than 15 Hz did not lead to better surgical outcomes.

Keywords: Frequency; Neuromodulation; Sacral Nerve Stimulation; Urinary Bladder, Overactive.

Fig. 1.

The pictures of real products: stimulator (A), stimulating electrode with 6 contact points (B), and extension cable (C).

Fig. 2.

The implantation process of SacralStim (General Stim Inc., Hangzhou, China): placing the stimulation electrodes (A) and connecting the extension cable with the stimulator (B).

Fig. 3.

Radiographs show the leads passed through the S3 foramen: anteroposterior (A) and lateral (B).

Fig. 4.

Sacral nerve stimulation was given over a range of frequencies to suppress bladder overactivity induced by intravesical infusion of 5% acetic acid. The black bars under pressure trace indicate the stimulation duration. The short arrows indicate the start and stop of bladder infusions. Stimulation: pulse width 210 µsec, intensity 4 V. Infusion rate: 30 mL/min.

Fig. 5.

Sacral nerve stimulation inhibited bladder overactivity during 5% acetic acid infusion at 15 to 50 Hz. There were no significant differences among 15-, 30-, and 50-Hz frequencies (P>0.05). Stimulation: pulse width 210 µsec, intensity 4 V. NS, normal saline; AA, acetic acid; CMG, cystometrogram. *Statistically significant difference.