New Neurostimulation Strategy and Corresponding Implantable Device to Enhance Bladder Functions (2011)

among which are rhizotomy, and EUS blockade using high-frequency stimulation. Dorsal rhizotomy consists of selectively severing afferent sacral nerve roots that are involved in pathological reflex arc in suprasacral SCI patients. Rhizotomy abolishes DO, reduces DSD, and prevents autonomic dysreflexia. As a beneficial result, the uninhibited bladder contractions are reduced, the bladder capacity and compliance are increased, urine flow is improved, and consequently the upper urinary tract is protected from ureteral reflux and hydronephrosis. In case of a complete SCI, dorsal rhizotomy is combined with an www.intechopen.com Biomedical Engineering Trends in Electronics, Communications and Software 80 implantable sacral ventral root stimulator such as the Finetech-Brindley Bladder System (also known as the VOCARE in North America) (Kutzenberger, 2007). In fact, this neurostimulation system is the only commercialized and FDA-approved solution aiming for micturition in SCI patients Unfortunately, rhizotomy being irreversible, it has a fundamental disadvantage which is the abolition of sexual and defecation reflexes, as well as sacral sensations if still present in case of incomplete SCI. High-frequency stimulation can be used to inhibit the contraction of the EUS muscle. However, the mechanism by which the EUS inhibition is obtained is not well understood and three explanations are possible: high-frequency stimulation may stop the propagation of nerve action potentials, may maintain the motor end-plate (neuromuscular junction) in a refractory status, or may fatigue the aimed muscle Frequencies from 300 Hz to 30 kHz can be used to achieve a complete and reversible nerve conduction block depending on the stimulation amplitude However, below 1 kHz, a sinusoidal stimulation can generate action potentials at the same or a submultiple rate. Increasing the frequency has the advantage of lowering the amount of injected charge per-phase needed for a complete blockade. A graded blockade can also be achieved as blockade of each axon within the nerve is influenced by its diameter and the stimulation amplitude If a graded blockade is applied distally in combination with low-frequency stimulation, selectivity with respect to axon diameter can be obtained by adjusting stimulation amplitude Finally, combining sacral root stimulation with bilateral high-frequency pudendal nerve block led to effective micturition in male cats The efficiency of high-frequency blockade was studied with dog experiments using a neurostimulator designed by Polystim Neurotechnologies Laboratory The Polystim's stimulator generated a rectangular waveform combining two frequencies (e.g. 600 Hz and 30 Hz). It is important to point out in this case, that stimulation and blockade are both applied simultaneously at the same nerve site, with the same bipolar electrode. According to Kilgore et al. The same neurostimulator was also implanted in paraplegic dogs for chronic experiments where it was demonstrated that the combination of low and high frequency stimuli resulted in 45 % reduction in EUS activity and that urine evacuation improved up to 91 % of the mean bladder capacity during the six months of chronic stimulation The latest Polystim's neurostimulation prototypes using that stimulation strategy were UroStim6 and UroStim7 presented in This chapter first describes a new sacral neurostimulation strategy to enhance micturition, based on nerve conduction blockade using high frequency stimulation as an alternative to rhizotomy. In order to test this strategy in chronic animal experiments, an implantable neurostimulation device is required. Thus, this chapter presents the design, test, prototyping and encapsulation of such neurostimulator (UroStim8) implementing the proposed stimulation strategy and using only commercially available discrete components.