Selective activation of the sacral ventral roots for control of urinary bladder function

Low-pressure continuous bladder voiding was induced by selective activation of small diameter motor fibers in the sacral anterior roots. The spinal roots innervating the urinary bladder were selectively activated by Quasitrapezoidal current pulses applied through tripolar spiral nerve electrodes.; The initial experiments focused on the causes of obstruction to voiding. Urethral pressure profiles recorded in chronically implanted female animals, with and without sacral root stimulation, showed that the highest sphincter pressures were recorded in the ventral orientation near the terminal portions of the urethra. Stimulation with 20 Hz pulse trains did not elicit increased pressures in the proximal parts of the urethra when the bladder was empty. With the bladder filled, the pressures in the proximal urethra followed the bladder pressure. Sphincter responses were significantly higher with the bladder filled. Tests with an open-ended rigid catheter showed fluid entry into the proximal 80% length of the urethra during root stimulation. Results from tests with a Foley balloon catheter occluding the bladder neck, showed that occlusion caused a significant decrease in the reflex pressure responses at the sphincter. These results were interpreted to indicate that fluid entering the bladder neck triggered a reflex contraction of the urinary sphincter, probably through stretch receptors in the bladder neck region. A dorsal rhizotomy is recommended to avoid this reflex contraction. Fatigue appeared to be a major factor in the experimental design. There was progressive reduction in the evoked bladder pressure during experimental sessions, with an average decrease of 50% after a set of twelve pulse trains.; A new protocol of acute experiments was designed that called for early rhizotomy and limited number of trials. Continuous, low-pressure voiding occurred during stimulation with quasitrapezoidal pulse trains with significantly lower bladder and outlet pressures in five adult male and female dogs. The results show that this method induced mean flow rates comparable to clinically implemented procedures for intermittent stimulation. Selective activation of the sacral ventral roots can provide a viable means of low-pressure continuous voiding of the urinary bladder in neurological impairments.