SELECTIVE SACRAL ROOT STIMULATION FOR BLADDER CONTROL - ACUTE EXPERIMENTS IN AN ANIMAL-MODEL

High bladder pressure is a potential side effect of poststimulus voidi ng, used to date for stimulation-induced bladder emptying in spinal co rd injured patients. To prevent this side effect, selective activation of the bladder without activation of the urethral sphincter by select ive stimulation of sacral roots was studied in a canine animal model. On-line registration of bladder, urethral and rectal pressure was perf ormed, and EMG of tail muscles and urethral sphincter was recorded. Af ter laminectomy, intradural left and right sacral root S-2 were stimul ated with a tripolar cuff electrode. A self-made stimulator generating adjustable pulse shapes was used. Using 200 mu sec. rectangular pulse s, contraction of bladder and urethral sphincter could be elicited. Se lective activation of the bladder occurred with pulses of 600 to 800 m u sec. due to anodal blocking of the large nerve fibers in the sacral roots. During acute animal experiments we were able to achieve selecti ve activation of the detrusor without simultaneous activation of the e xternal urethral sphincter, and complete, low-pressure voiding occurre d.