Electrical stimulation to control bladder function after supra-sacral SCI has been under investigation for several decades. Stimulation at various levels of the neurourologic axis has been attempted. In Great Britain, Brindley and Rushton (1990) has had the most experience and success with S2 through S4 anterior sacral nerve root stimulation in combination with posterior rhizotomy. This system is surgically implanted through lumbar laminectomy and employs either epidural or intradural electrodes. Electrodes are connected via cable to an implanted radio receiver, which couples to an external stimulator/transmitter. Pulsed stimulation is used to take advantage of the differences between activation of the slow response smooth musculature of the detru-sor (bladder) and activation of the fast twitch striated sphincter musculature (Fig. 9.6). Bladder pressure gradually increases in a tetanic fashion, while sphincter pressure rapidly falls after the end of each stimulation pulse. This produces short spurts of urination that result in nearly complete bladder emptying.
Potential candidates for the Vocare implant need to have intact parasympathetic efferent neurons to the detrusor musculature (see Volume II, Chapter 24). This can be ascertained by cysometrogram recording of bladder pressure (Creasey, 1999). In order to provide continence of urine with this device, one has to abolish reflex incontinence caused by activation of the sensory reflex pathway. This has been done by performance of a sacral posterior rhizo-tomy. This procedure abolishes uninhibited reflex bladder contractions and restores bladder compliance. Detrusor-sphincter dyssynergia is also reduced, thereby avoiding the chance of autonomic dysre-flexia. The downside of this procedure, however, is loss of perineal sensation in sensory incomplete individuals and loss of reflex erection and ejaculation if present.
Over 1500 sacral anterior root stimulators have been implanted. Of those approximately 90% are in regular use 4-6 times per day. In the USA, the FDA approved the implantation of the device in 1998 under the trade name Vocare™.
In a study of 20 patients, post-void residual volumes were reduced on average from 212 to 22 ml with the Vocare system (Van Kerrebroeck et al., 1993). A significant reduction in the number of
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