Induction of urethral closure and inhibition of bladder contraction by continuous magnetic stimulation

Magnetic stimulation has been considered to be a technique for stimulating nervous system noninvasively and it has been used for experimental and clinical testings on the central and peripheral nervous systems. However, commercially available magnetic stimulators can only discharge single pulses for less than several minutes because the coil soon overheats. We newly devised a continuous magnetic stimulator assuring long-time stimulation, and this study was designed to confirm whether continuous magnetic stimulation would result in urethral closure and inhibition of bladder contraction in anesthetized canine models. Twelve female beagle dogs, weighing 9 to 12 kg, were anesthetized with a mixture of alpha-chloralose and urethane. In six beagles, a 4 F microtip transducer was inserted transurethrally, and maximum intraurethral pressure was monitored. In the remaining six animals, urethra was ligated at the bladder neck and a 4 F double lumen catheter was inserted from the dome of the bladder to infuse physiological saline, monitoring iso-volumetric rhythmic bladder contraction. The stimulating coil, of which temperature was kept at 20-25 degrees C by the built-in cooling system, was placed on the ishio-rectal fossa to stimulate the pudendal nerve at 10 Hz. The intraurethral pressure increased by 69.1 +/- 27.8 cm H(2)O, and iso-volumetric rhythmic bladder contraction was inhibited during the stimulation with 80% (240 Joule) of maximum output. In conclusion, continuous magnetic stimulator was found effective for urethral closure and inhibition of bladder contraction. Neurourol. Urodynam. 18:505-510, 1999.