Morten Voss Fjorback

A portable device for experimental treatment of neurogenic detrusor overactivity.

The objective of this study was to evaluate the effect of automatic event‐driven electrical stimulation on the dorsal penile/clitoral nerve for management of neurogenic detrusor overactivity in spinal cord injured subjects. In order to reach the objectives it was necessary to design and realize a portable device for ambulatory urodynamic studies which was able to activate an electrical stimulator when the detrusor pressure exceeded a certain threshold. The developed device was repeatedly tested in a healthy subject and subsequently tested in a spinal cord injured subject. In testing the automatic event‐driven system in the spinal cord injured subject, detrusor contractions were successfully inhibited until a certain bladder volume was reached and no incontinence episodes were observed prior to disabling the system. The preliminary results indicate that automatic event‐driven electrical stimulation on the dorsal penile/clitoral nerve can inhibit involuntary detrusor contractions in spinal cord injured subjects and hereby restore continence and increase bladder capacity.

Electrical Stimulation of Sacral Dermatomes in Multiple Sclerosis Patients With Neurogenic Detrusor Overactivity

AIMS Transcutaneous electrical stimulation of the dorsal penile/clitoral nerve (DPN) has been shown to suppress detrusor contractions in patients with neurogenic detrusor overactivity (NDO). However, the long-term use of surface electrodes in the genital region may not be well tolerated and may introduce hygienic challenges. The aim of this study was to assess whether electrical stimulation of the sacral dermatomes could suppress detrusor contractions in multiple sclerosis (MS) patients with NDO, hereby providing an alternative to DPN stimulation. MATERIALS AND METHODS A total of 14 MS patients (8 M, 6 F) with low bladder capacity (<300 ml) and a recent urodynamic study showing detrusor overactivity incontinence participated in the study. Three successive slow fill cystometries (16 ml/min) were carried out in each patient. The first filling served as control filling where no stimulation was applied. In the second and third filling electrical stimulation of either the DPN or sacral dermatomes was applied automatically whenever the detrusor pressure exceeded 10 cmH2O. RESULTS The control filling showed detrusor overactivity in 12 of the 14 patients. In 10 of the 12 patients one or more detrusor contractions could be suppressed with DPN stimulation. Electrical stimulation of the sacral dermatomes failed to suppress detrusor contractions in all patients. CONCLUSIONS Although therapeutic effects may be present from stimulation of the sacral dermatomes, we were unable to demonstrate any acute effects during urodynamics. For this reason stimulation of the sacral dermatomes is not an option in a system that relies on the acute suppression of a detrusor contraction.

Boron-Doped Nanocrystalline Diamond Electrodes for Neural Interfaces: In vivo Biocompatibility Evaluation

Boron-doped nanocrystalline diamond (BDD) electrodes have recently attracted attention as materials for neural electrodes due to their superior physical and electrochemical properties, however their biocompatibility remains largely unexplored. In this work, we aim to investigate the in vivo biocompatibility of BDD electrodes in relation to conventional titanium nitride (TiN) electrodes using a rat subcutaneous implantation model. High quality BDD films were synthesized on electrodes intended for use as an implantable neurostimulation device. After implantation for 2 and 4 weeks, tissue sections adjacent to the electrodes were obtained for histological analysis. Both types of implants were contained in a thin fibrous encapsulation layer, the thickness of which decreased with time. Although the level of neovascularization around the implants was similar, BDD electrodes elicited significantly thinner fibrous capsules and a milder inflammatory reaction at both time points. These results suggest that BDD films may constitute an appropriate material to support stable performance of implantable neural electrodes over time.

Electrochemical properties of titanium nitride nerve stimulation electrodes: an in vitro and in vivo study.

The in vivo electrochemical behavior of titanium nitride (TiN) nerve stimulation electrodes was compared to their in vitro behavior for a period of 90 days. Ten electrodes were implanted in two Göttingen minipigs. Four of these were used for electrical stimulation and electrochemical measurements. Five electrodes were kept in Ringers solution at 37.5°C, of which four were used for electrical stimulation and electrochemical measurements. The voltage transients measured in vivo were 13 times greater than in vitro at implantation and they continued to increase with time. The electrochemical properties in vivo and the tissue resistance (Rtissue) followed a similar trend with time. There was no consistent significant difference between the electrochemical properties of the in vivo and in vitro electrodes after the implanted period. The differences between the in vivo and in vitro electrodes during the implanted period show that the evaluation of electrochemical performance of implantable stimulation electrodes cannot be substituted with in vitro measurements. After the implanted period, however, the performance of the in vivo and in vitro electrodes in saline was similar. In addition, the changes observed over time during the post-implantation period regarding the electrochemical properties of the in vivo electrodes and Rtissue were similar, which indicates that these changes are due to the foreign body response to implantation.

Comparison of the electrochemical properties of smooth and porous TiN electrode coatings in rats

Eight smooth and 8 porous titanium nitride (TiN) coated electrodes were implanted in 8 rats. Before implantation, voltage transients (VTs), cyclic voltammograms (CVs) and impedance spectra were recorded in phosphate buffered saline (PBS). During the implanted period, these measurements were repeated weekly. The VTs and CVs at high sweep rates of the porous electrodes were more affected by implantation as compared to the smooth electrodes. The charge injection (Qinj) and charge storage capacity (CSC) of both electrode types decreased during the first 3 weeks after implantation. This indicates that protein adhesion directly after implantation presents a diffusion limitation for the porous electrodes only, while cell adhesion limits diffusion for both smooth and porous electrodes.

Increasing Voltage Transients Using Implanted Titanium Nitride Neural Stimulation Electrodes

The electrochemical properties of porous titanium nitride (TiN) stimulation electrode coatings were investigated in vivo in the chronic setting. Four titanium pins were coated with porous TiN and implanted in the pelvic region of two minipigs. Electrochemical impedance spectroscopy (EIS) was performed daily, while voltage transient measurements (VTM), electrical stimulation and cyclic voltammetry (CV) were performed every other week. Electrical stimulation was applied successfully during the course of the study. Voltage transients and tissue impedance increased, while charge storage decreased during the first 3-4 weeks after implantation. This is most likely related to encapsulation of the electrode.

Chronic Electrochemical Investigation of Titanium Nitride Stimulation Electrodes in vivo

For neural prostheses to be successful, good performance of neurostimulation electrodes is important. An important aspect of this is electrochemical stability and corrosion resistance. The electrochemical performance of 4 thin film titanium nitride (TiN) electrodes is investigated in a porcine animal model. In vivo impedance measurements have been made for 3 months to investigate the electrode-tissue interface and to monitor tissue resistance in vivo. The tissue resistance was low in the first week, after which it increased and stabilized. After 50 days, a dramatic change is observed in the electrode-tissue interface; charge is transferred via faradic instead of capacitive pathways. This is likely due to anodic oxidation of the TiN surface. This was not reversed, but no signs of further oxidation were observed. Neither the tissue nor the electrode appeared damaged after explantation.

Wavelet packet analysis for angular data extraction from muscle afferent cuff electrode signals

Rehabilitation devices can greatly benefit from the use of natural sensors. Thus, we have extended on our efforts to extract angular information from muscle afferent nerves by means of cuff electrodes. Is this study we applied wavelet analysis to electroneurographic (ENG) data from rabbits. In order to estimate ankle flexion/extension angles, we recorded ENG signals from the left Tibial and Peroneal nerves, both during FES and under passive motion. Several processing methods were used for extraction of angular data and were compared with the wavelet analysis. An artificial neural network (ANN) was used with the analyzed features to improve on the accuracy of the angular predictions. The network has so far been tested for local generalization only. The ANN was found to work better with the wavelet features than with previously explored rectified and bin integrated (RBIN) signals. Best results were obtained by using ANN inputs that consisted of both the output from a single wavelet packet node and the RBIN signal: the mean angle prediction error was 1.2/spl deg/. Exciting as this result is, we must keep in mind that due to the local generalization scope of this study, angle predictions have yet to be assessed regarding inter-rabbit variability.

Influence of fibrous encapsulation on electro-chemical properties of TiN electrodes

The aim of this study was to investigate how the electrochemical properties of porous titanium nitride stimulation electrode are affected by fibrous encapsulation in vivo. Electrochemical impedance spectroscopy (EIS), cyclic voltammetry and voltage transient (VT) measurements were performed in vivo and in phosphate buffered saline, where the encapsulation process is absent. EIS was used as a non-invasive measurement to follow the inflammation, healing and encapsulation process. EIS showed that the healing and encapsulation process lasted 3-4 weeks. The VTs increased during the first 3-4 weeks, after which they stabilized. The charge storage capacity (CSC) decreased most during the first 3-4 weeks. The increasing VTs and decreasing CSC during the first 3-4 weeks after implantation of the in vivo electrodes seem related to healing and fibrous encapsulation. It is suggested that the charge injection pathway during the encapsulation process changes, which implies that charge injection limits are underestimated with conventional methods.

Influence of implantation on the electrochemical properties of smooth and porous TiN coatings for stimulation electrodes

OBJECTIVE To determine whether changes in electrochemical properties of porous titanium nitride (TiN) electrodes as a function of time after implantation are different from those of smooth TiN electrodes. APPROACH Eight smooth and 8 porous TiN coated electrodes were implanted in 8 rats. Before implantation, voltage transients, cyclic voltammograms and impedance spectra were recorded in phosphate buffered saline (PBS). After implantation, these measurements were done weekly to investigate how smooth and porous electrodes were affected by implantation. MAIN RESULTS The electrode capacitance of the porous TiN electrodes decreased more than the capacitance of the smooth electrodes due to acute implantation under fast measurement conditions (such as stimulation pulses). This indicates that protein adhesion presents a greater diffusion limitation for counter-ions for the porous than for the smooth electrodes. The changes in electrochemical properties during the implanted period were similar for smooth and porous TiN electrodes, indicating that cell adhesion poses a similar diffusion limitation for smooth and porous electrodes. SIGNIFICANCE This knowledge can be used to optimize the porous structure of the TiN film, so that the effect of protein adhesion on the electrochemical properties is diminished. Alternatively, an additional coating could be applied on the porous TiN that would prevent or minimize protein adhesion.