Impact of electrostimulation of neurovascular bundles and pudendal nerves on the membranous urethra in male rabbits.

PURPOSE: The pathophysiology of post-prostatectomy incontinence is supposed to be multifactorial. The impact of the neurovascular bundles on sphincter function is still under debate. We clarified the impact of cavernous nerves function on the MU. We compared MU pressure responses in male rabbits following electrophysiological stimulation trials on the neurovascular bundles vs pudendal nerve stimulation. MATERIALS AND METHODS: Six male Chinchilla Bastard rabbits were included in this study. Pudendal and cavernous nerve branches were exposed bilaterally in all animals. Randomized electrostimulation of pudendal nerve fibers and the cavernous nerves, as confirmed by erection,) were done using a biphasic signal form of 0.3 mA for 200 microseconds. Stimulation frequency was changed in a randomized pattern from 10 to 40 Hz. Changes in MU pressure were measured urodynamically via a transurethral microtip catheter placed in the MU. Stimulation responses of the 2 nerve structures were compared. RESULTS: Mean baseline pressure in the MU without stimulation was 23 cm H(2)O (range 20 to 25) in all animals. During unilateral pudendal stimulation the mean pressure response increased highly significantly to 33, 43, 59 and 60 cm H(2)O at 10, 20, 30 and 40 Hz, respectively (p <0.005). In contrast, compared to baseline pressure cavernous nerve stimulation did not result in any significant changes in proximal urethral pressure (mean 23 cm H(2)O, range 20 to 25, p >0.05). CONCLUSIONS: Our results confirm the primacy of the pudendal nerve in the external urethral sphincter innervation. In contrast, stimulation of the cavernous nerves did not produce any pressure changes in the MU. These results confirm that the neurovascular bundles have no functional impact on the MU.

[Sacral neuromodulation in patients with nonobstructive, chronic urinary retention: relevance of the carbachol test and influence of associated nerve lession]. / Sakrale Neuromodulation bei nichtobstruktiver, chronischer Harnretention: Die Wertigkeit des Carbacholtests und der Einfluss der assoziierten Nervenläsion.

OBJECTIVE: Aim of this study was to evaluate whether the carbachol test and the nerve lesions responsible for bladder dysfunction possess predictive value in patients with chronic urinary retention who undergo temporary sacral neuromodulation (PNE test). MATERIAL AND METHODS: In 1999 and 2000, PNE tests were performed in 24 patients with chronic urinary retention and acontractile detrusor previously assessed by urodynamics. In 18 patients, a carbachol test was performed during urodynamics. The diagnosis related to the acontractile detrusor was additionally assessed and compared to the successful outcome of the PNE test. RESULTS: The PNE test was successful in 8 of the 24 patients (33.3 %). The bladder was completely emptied during the PNE test in 3 of the 10 patients with negative carbachol test and in 3 of the 8 patients with positive carbachol test. The highest success rate (80 %) was observed in patients after hysterectomy, whereas after lumbosacral pulposal prolapse or with a CNS tumor, it was only 20 - 33.3 %. CONCLUSIONS: We conclude that sacral neuromodulation is an effective treatment option in patients with nonobstructive urinary retention. The carbachol test does not possess any definitive predictive value with respect to the success rate of sacral neuromodulation in patients with chronic urinary retention. The success rate more likely depends on the localisation of the nerve lesion. PNE tests should be performed in all patients with therapy resistent nonobstructive urinary retention, as no other predictive factors exist.

[Clinical Results of PNE Tests in 70 Patients with Different Bladder Dysfunctions]. / Klinische Ergebnisse nach 70 bilateralen peripheren Nerven-Evaluationstests (PNE-Test) bei Patienten mit Harnblasendysfunktionen.

PURPOSE: Prior to implantation of a sacral neuromodulator we carried out PNE tests (peripheral nerve evaluation test) with bilateral test stimulation to establish which patients might profit from this kind of therapy. In contrast to the original unilateral technique used by Tanagho and Schmidt, we performed bilateral PNE test stimulation. Moreover, we analysed the diagnostic characteristics of those patients who had positive PNE test results and could thus receive a chronic sacral neuromodulator. MATERIALS AND METHODS: We performed bilateral PNE test stimulation in 70 patients (mean age: 53.6 yrs; 41 with retention symptoms and 29 with a hyperactive detrusor) over a minimum of 3 days. Retrospectively, we analysed the distribution of diagnostic characteristics (retention vs. overactive bladder and neurogenic vs. idiopathic) in the implant recipients. RESULTS: All patients received bilateral PNE test stimulation, during which the stimulation amplitudes were adjusted individually for each side. 8 patients were treated with the original PNE-electrode (model 0 041 830 - 002, Medtronic Inc., USA) without success. Of the remaining 62 patients, who were treated with an improved electrode, the PNE test was successful in 32 cases (51.6 %). Twenty-seven of these patients suffered from a neurogenic bladder dysfunction, and, in 5 cases, the causes were idiopathic. CONCLUSIONS: Bilateral PNE-test stimulation and the use of advanced PNE electrodes (model 3057, Medtronic Inc., USA) led to a positive PNE result in 51.6 % of the tested patients. Of these, the group with neurogenic bladder dysfunctions showed the highest response rate. Compared with the success rates in the multicenter study, we were able to increase the overall PNE response rate significantly. For this reason, we prefer a bilateral PNE-test with side-specific stimulation.

Stimulation signal modification in a porcine model for suppression of unstable detrusor contractions.

OBJECTIVES: To investigate, in an experimental study, the efficacy of a different stimulation signal in a porcine model to suppress formalin-induced unstable detrusor contractions. The current mode of stimulation in peripheral nerve evaluation tests and sacral neuromodulation is based on rectangular signal shapes. Published reports, however, have revealed that up to 80% of patients do not respond to peripheral nerve evaluation stimulation. METHODS: After placement of electrodes at S3 in 12 anesthetized Göttinger minipigs, unstable contractions were induced by intravesical instillation of formalin. Ten-minute stimulation phases with a quasi-trapezoidal signal and a rectangular signal followed. An interval of 30 minutes elapsed between the two series of stimulations. The pressure values were registered on a urodynamic unit and evaluated as contractions and amplitudes per minute. Six minipigs were treated in the same way but were not stimulated and served as the control group. RESULTS: After formalin instillation, the average number of involuntary detrusor contractions was 3.5/min (+/- 0.8) and the sum of amplitudes was 7.2/min (+/- 1.1). Subsequent NaCl instillation and quasi-trapezoidal stimulation reduced the contractions to 0.3/min (+/- 0.3) and the sum of amplitudes to 0.8/min (+/- 0.4). A contraction rate of 1.1/min (+/- 0.1) and a sum of amplitudes of 5.1/min (+/- 2.4) were recorded under stimulation with a rectangular signal. In the control group, no significant reduction was recorded. CONCLUSIONS: The acquired data demonstrate that quasi-trapezoidal stimulation suppresses unstable detrusor contractions in the minipig more effectively than does conventional rectangular stimulation as presently applied in sacral neuromodulation.

[Chronic sacral bilateral neuromodulation. Using a minimal invasive implantation technique in patients with disorders of bladder function]. / Chronische sakrale bilaterale Neuromodulation. Einsatz einer minimalinvasiven Implantationstechnik bei Patienten mit Blasenfunktionsstörungen.

The implantable neuromodulation system described by Tanagho and Schmidt enables unilateral sacral nerve stimulation. Reports have been made on sacral neuromodulation failures of up to 50% in patients undergoing this procedure. We chose the bilateral electrode implantation and a minimal invasive laminectomy to ensure a more effective modulation and better placement and fixation of the electrodes. After successful assessment using a peripheral nerve evaluation test, 20 patients (14 with detrusor instability, 6 with hypocontractile detrusor) underwent minimally invasive laminectomy and bilateral electrode placement. In the patients with detrusor instability, the incontinence episodes were reduced from 7.2 to 1 per day and the bladder capacity improved from 198 to 352 ml. In patients with hypocontractile detrusor, the initial residual urine level of 450 ml dropped to 108 ml. Maximum detrusor pressure during micturition rose from 12 cmH2O initially to 34 cmH2O. The average follow up period was 17.5 months. There was no sign of deterioration in the modulation effect in any of the patients. Bilateral electrode implantation and the new sacral approach allow optimal neuromodulation in patients with bladder dysfunction. Laminectomy enables optimum electrode placement and fixation with minimal trauma.

Threshold-distance measures from electrical stimulation of human brainstem.

Threshold current levels for electrical stimulation of a single human brainstem via an auditory prosthesis are compared with postmortem measures of the distance between the electrode and stimulated structures. The results compare well with the summary of threshold-distance measures from animal experiments compiled by Ranck. The correspondence between the human and animal data gives confidence that the extent of current spread (distance to stimulable neural units) can be well estimated from the current level at threshold for 200 microseconds/phase biphasic pulses. This is of particular interest in electrical stimulation of the human central nervous system, where localization of stimulation is of paramount importance.

Hypothalamic neuron projection to autonomic preganglionic levels related with glucose metabolism: a fluorescent labelling study in the rat.

The location of hypothalamic paraventricular neurons projecting to sympathetic preganglionic levels and related to the autonomic regulation of various organs involved in glucose metabolism (OGM) was determined by ipsilateral injections of two fluorescent tracers, Diamidino Yellow into the left dorsal motor nucleus of the vagus and Fast Blue into the left intermediolateral cell column of the T8-T9 spinal cord. Hypothalamospinal neurons were mainly located in the dorsal part of the paraventricular hypothalamic nucleus (PVH) and the hypothalamobulbar neurons were most abundant in the ventral, medial and extreme lateral parts of the PVH. No double-labelled neurons were found in the hypothalamus. These results can help the knowledge of the neural hypothalamic network related with the autonomic hypothalamic control.

Electrical stimulation of the auditory brain stem structure in deafened adults.

Electrical stimulation of the cochlear nuclear complex in the brain stem was first accomplished in a female adult deafened by bilateral acoustic tumors. The central electroauditory prosthesis (CEP) was surgically placed at the time of the second tumor removal. The patient has now been receiving electrical stimulation for 5 years. Six more adults have received the CEP at the time of tumor surgery. Clinical results indicate fluctuations in electrical measurements over time, particularly in the first weeks following surgery. Patients are able to sustain tone perception for one minute at all frequencies tested. Auditory discrimination test results reveal above-chance performance on suprasegmental measures, similar to scores achieved by cochlear implant users. No serious complications have occurred to date.