Selective activation of the urinary bladder with quasi-trapezoidal pulses in sacral anterior root stimulation in the dog

Experiments have been performed to receive a selective stimulation of the urinary bladder in sacral anterior root stimulation in the foxhound dog. A computer controlled stimulator system has been developed to create arbitrary shaped current pulses using a commercially available universal source. Different monophasic and biphasic quasitrapezoidal (QT-) pulses have been created to investigate the influence of slew rates and pulse shapes on the selectivity of myelinated and unmyelinated nerve fibers. Following bilateral deafferentation of the sacral roots S1 to S3, the anterior roots S2 were placed into tripolar book electrodes with one cathode and two adjacent anodes. The pressure of the urethral sphincter and the detrusor were monitored during experiments by urodynamic investigation (microtip-catheter). Short stimulation pulse trains were applied and the sphincter response was monitored at six different pulse shapes. At some pulse shapes, an anodal block of the urethral sphincter was observed. In these cases longer pulse trains were applied to monitor the bladder response. A positive pressure difference could be observed in mono- and biphasic QT-pulses. In one case, a non-intermitting voiding in continuous bilateral stimulation of the anterior roots S2 was seen.