Afferent nerve activity from the dermatome, bladder and rectum can be recorded using cuff electrodes placed on the extradural S3 sacral root in humans but improvements in recording quality and sophisticated signal processing methods are needed for chronic application.

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The ability to stimulate subareas of a nerve selectively is highly desirable, since it has the potential of simplifying surgery to implanting one cuff on a large nerve instead of many cuffs on smaller nerves or muscles, or alternatively can improve function where surgical access to the smaller nerves is limited. In this paper, stimulation was performed with a four-channel multipolar cuff electrode implanted on the sciatic nerve of nine rabbits to compare the extensively researched longitudinal tripolar configuration with the transverse tripolar configuration, which has received less interest. The performance of these configurations was evaluated in terms of selectivity in recruitment of the three branches of the sciatic nerve. The results showed that the transverse configuration was able to selectively activate the sciatic nerve branches to a functionally relevant level in more cases than the longitudinal configuration (20/27 versus 11/27 branches) and overall achieved a higher mean selectivity [0.79 ± 0.13 versus 0.61 ± 0.09 (mean ± standard deviation)]. The transverse configuration was most successful at recruiting the small cutaneous and medium-sized peroneal branches, and less successful at recruiting the large tibial nerve.

Abstract-Intraoperative recoding of ENG from the S3 extradural sacral nerve roots was performed in 2 SCI patients. The goal of this work was to study the relation between mechanical stimulation of the urinary bladder, rectum and skin and the resulting ENG-signals. These signals could be used to detect the onset of a bladder contraction. This concept could be used in an implantable neuroprostheses to treat detrusor hyperreflexia. The recorded human signals are consistent with data from animal studies. However, more human studies are needed. Keywords -Sacral nerve roots, urinary bladder, detrusor hyperreflexia, electrical stimulation, ENG. I. INTRODUCTIONDetrusor hyperreflexia (DH) is the most common form of detrusor dysfunction in spinal cord injury and causes a failure of the storage function of the lower urinary tract. It is characterized by involuntary detrusor contractions during bladder filling at relative small volumes which cannot be suppressed consciously and cause an increase in intravesical pressure of more than 15 cm H 2 O. DH causes a low storage capacity and transient high intravesical pressures resulting in incontinence, risk for kidney damage and bladder hypertrophy.The first step in the treatment of DH is medication. However, pharmacological inhibition of DH (e.g. by oxybutynin) is often unsuccessful and its usefulness is limited by intolerance to oral administration due to side effects as salivary reduction with dry mouth, vision disturbance and inhibition of gut motility [1]. Especially in patients with SCI these side effects are very troublesome. In the case of failure of the drug, destructive treatments are advocated such as surgical augmentation of the bladder [2] and surgical deafferentation of the bladder [3].An alternative option is the use of electrical stimulation. The ratio of this treatment modality is based on the existence of spinal inhibitory systems which are capable of interrupting a detrusor contraction. These inhibitory systems can be activated by electrical stimulation of appropriate afferent nerve fibers. Electrical stimulation would therefore be a nondestructive alternative for patients who are refractory to drugs or cannot tolerate the side effects.Bladder inhibition can be achieved by stimulation of afferent anorectal branches of the pelvic nerve, the dorsal penile/clitoris nerve [4], the pudendal nerve and the dorsal sacral nerve roots [5]. Several studies have shown that electrical stimulation of these afferents may have long lasting effects on bladder inhibition in non-neuropathic bladder dysfunction. However, this is not the case in neuropathic bladder dysfunction [6]. So chronic stimulation is needed.The stimulator could be on continuously during the filling phase although stimulation is actually only needed to inhibit a contraction. The stimulator could thus be turned off if no reflex contractions are present. In order to allow event driven stimulation a sensor is needed that detects the onset of a contraction.Implantable sensors with sufficiently long biocompatibilit...

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