Reduction of bladder outlet resistance by selective stimulation of the ventral sacral root using high frequency blockade: A chronic study in spinal cord transected dogs

Purpose: The use of electrical neural stimulation as treatment for neurogen ic bladder is complicated by simultaneous contraction of the striated sphin cter. This result is due to the composition of the ventral sacral roots, wh ich contain somatic fibers innervating the external urethral sphincter and preganglionic parasympathetic fibers innervating the detrusor, among others . The somatic fibers have a larger caliber than the parasympathetic fibers and, as large diameter fibers, need a lower stimulus amplitude for activati on than smaller fibers. Activation of the smaller fibers is always accompan ied by activation of the larger fibers. We studied the effect of chronic ap plication of selective combined low and high frequency current stimulation of the ventral sacral root on bladder evacuation and urethral resistance in chronically spinalized (spinal cord transected above the spinal micturitio n center) male dogs for daily bladder evacuation. Materials and Methods: A total of 14 male mongrel dogs weighing 20 to 25 kg . underwent transection of the spinal cord at the T10 vertebra. The S2 vent ral sacral root was wrapped with a bipolar electrode connected to a subcuta neous microstimulator. Daily bladder evacuation by neural stimulation with determination of the voided and residual urine volumes was done for 8 month s. The animals were stimulated only with low frequency current during the 1 -month spinal shock phase. Selective parameters of combined low frequency s timulation and high frequency blockade currents were subsequently applied f or 6 months. For the last study month the animals were again stimulated by low frequency current alone. Bladder and urethral pressure as well, as elec tromyography of the external urethral sphincter and pelvic floor muscles we re evaluated monthly. Histopathological testing of the chronically stimulat ed nerve and external sphincter was performed. Results: Of the 14 dogs 12 completed the followup study. During the shock p hase with the application of low frequency only stimulation the animals voi ded 26% of mean functional bladder capacity with the early return of detrus or activity. Mean detrusor pressure plus or minus standard error of mean wa s 76.4 +/- 21.6 cm. water, while mean urethral pressure was 83.6 +/- 16.8 c m. water. During the application of selective combined low and high frequen cy stimulation 7 animals (58%) evacuated the bladder completely with post-v oid residual urine less than 10% of mean individual functional bladder capa city and 5 (42%) had mean post-void residual urine less than 20% of mean in dividual bladder capacity. Mean detrusor pressure was 73.5 +/- 20 cm. water and mean urethral pressure was 44 +/- 7.3 cm. water. There was a 45.19% re duction in the mean electromyography activity of the external sphincter. St imulation of the dogs for the last month by low frequency current resulted in the voiding of 33% of mean bladder capacity with an increase in mean ure thral pressure and electromyography activity. Conclusions: These results of reducing external sphincter activity by the s imultaneous application of high frequency current blockade of the somatic f ibers and activation of the autonomic fibers of the bladder by low frequenc y stimulation are promising.