Neurostimulation of the sacral roots in neurogenic bladder : the effect of selective high-frequency blockade on external urethral sphincter activity

Bladder dysfunction secondary to neurologic impairment can be caused by any pathologic condition affecting the central or peripheral nervous system or both (brain lesions, cerebrovascular accidents, multiple sclerosis, Parkinson's disease, spinal cord injury, myelodysplasia, etc.). Among those pathologies, the spinal cord injury (SCI) at the suprasacral level leads to the development of detrusor hyperreflexia associated with detrusor-external sphincter dyssynergia. The dyssynergic voiding results in a high voiding pressure which is the origin of upper urinary tract damage observed in spinal cord injured patients.The ultimate goals of the management of neurogenic bladder in suprasacral SCI are to achieve low-pressure urine storage, low-pressure and adequate urine emptying, control of detrusor hyperreflexia and catheter-free state. Different attempts varying from medication to sphincteric surgery or denervation have been tried in the past few decades to achieve these goals. The use of neurostimulation to achieve some of these outcomes in neurogenic bladder had also been attempted in the past with variable results.Electrical stimulation of selective sacral roots has been used in the management of neurogenic bladder secondary to SCI. However, since the ventral S$ sb2$ root contains mixed somatic fibers innervating the external sphincter and autonomic fibers innervating the bladder, electrostimulation of this root could even worsen the dyssynergia. In this acute canine work, we evaluated the feasibility of the principle of selective high frequency blockade of the somatic component of the sacral root. A stimulus was delivered by a new functional stimulator via a single bipolar electrode. This stimulus is composed of two independent current waveforms. The selectivity is caused by the inhibition of the somatic fibers by the high frequency component while the autonomic fibers are stimulated by low frequency stimuli. Using this technique of high-frequency blockade, we evaluated and showed the possibility of reduction of bladder outlet resistance during simultaneous detrusor contraction thus achieving a normal physiologic pattern of micturition