Reduction of bladder outlet resistance by selective sacral root stimulation using high-frequency blockade in dogs: an acute study.

Detrusor-sphincter dyssynergia is a main problem in supra-sacral spinal cord injured patients. The problem of high pressure voiding is also encountered in most electrically induced micturition because of the mixed somatic and autonomic fiber components of the ventral sacral root. We studied the effect of selective high-frequency blockade at the sacral nerve root in an acute spinalized canine model to prevent the deleterious consequences associated with the elevated bladder outlet resistance. A new functional electrical stimulation system which can generate one signal composed of two independent adjustable current waveforms delivered via a single bipolar electrode was used in 11 dogs. The selectivity resulted from the inhibition of the sphincteric somatic innervation by a high frequency pulse while the low frequency stimuli activated the bladder autonomic fibers. Bladder and urethral pressure as well as electromyograms of external urethral sphincter were recorded to determine whether selective high-frequency blockade occurred. Our experiments showed that we were able to achieve selective blockade of the external urethral sphincter during the simultaneous detrusor stimulation, thus obtaining a more physiologic voiding.