Effect of sacral nerve stimulation on autonomic nerve function

Background: Sacral nerve stimulation has been used successfully to treat motility disorders of the bladder and bowel. The mechanism of action remains unknown. This study examined the effect of stimulation on rectal blood flow as a measure of autonomic nerve function. Methods: Sixteen patients (15 women) of median age 59 (range 38-71) years were studied. All had undergone permanent electrode implantation for faecal incontinence, a median of 27 (range 2-62) months previously, with clinical benefit. Rectal laser Doppler flowmetry was performed at the level of chronic stimulation, without stimulation, and then at 0.1-V stepwise increments between zero and 1.0 V, and at 1-V increments to 5 V. Results: There was a significant difference in the median flux between no stimulation and chronic stimulation: 545 (range 355-887) versus 869 (range 507-989) fluxunits (P = 0.001). Stepwise increments of 0.1 V, between zero and 1.0 V, caused a significant immediate rise in flux (P < 0.001). Further increments did not result in any further significant increase. Conclusion: Chronic sacral nerve stimulation has a significant effect on rectal blood flow and the autonomic innervation of the distal. bowel. The response is rapidly reversible and varies in a dose-dependent manner up to a level of stimulation of 1.0 V.