Volume 8, Issue 3 - Proceedings of the 14th Vienna International Workshop on Functional Electrical Stimulation; Guest Editors: Winfried Mayr and Manfred Bijak

Polysynaptic activity is necessary to engage the neural circuitry that controls the motor behaviour and is crucial to the recovery after spinal cord injury (SCI) [1]. Polysynaptic responses can be elicited with spinal cord stimulation, and there are few reports on these types of responses in human electrophysiology, most of them describing them as constant to fixed stimuli. However, we have observed that the responses fluctuate in amplitude and time. Amplitude variations can be analysed with statistical methods. However, time fluctuations are more complex due to the multiple parameters involved. This work describes a methodology to analyse the time fluctuation in the responses of each pulse. It is based on the calculation of the signal temporal centroid, representing the whole activity, weighted by its latency, in a single time value. This value is then used to model the temporal fluctuation with linear regression. The methodology was verified with an electromyography dataset from a discomplete spinal cord injured patient with spinal cord stimulation. The parameter is able to follow small changes in the responses' distribution. Examples of how the temporal centroid and linear model identify the fluctuations are presented. Once fitted in a linear model, the fluctuation coefficient describes time fluctuations in the interneuron processing and, together with amplitude metrics, can characterise changes in polysynaptic responses during the application of fixed stimulation parameters.

Retinal implants allow patients suffering from degenerative retinal diseases to regain visual percepts. Despite considerable effort in developing and improving retinal neuroprostheses in the last decades, the restored vision in patients does not achieve sufficient quality. The elicited percepts do not accurately match the stimulating pixels and therefore the formation of high acuity vision is hindered. One of the main obstacles in epiretinal implants is the concurrent activation of cells close to a stimulating electrode and cells that have their axons traversing the electrode. In this study, we use computational modeling to examine the effect of pulse duration on the selectivity of focal versus non-focal activation. Our results suggest that biphasic pulses in the range of 10-20 microseconds can prevent axonal activation while still reliably activating target neurons.

Walking gait correction is fundamental to restoring body motion function for patients. Functional Electrical Stimulation (FES) is regarded as a promising method and essential to Neurotherapy, and the exoskeleton is fast becoming a key instrument in rehabilitation. Applying FES or exoskeleton alone, however, has its inherent disadvantages. Therefore, the hybrid exoskeleton combined with FES promoted in recent years overcomes the deficiency of more degree of freedom control. In this paper, a hybrid FES-Exoskeleton for walking gait control was first proposed and evaluated. With the Force Sensing Resistors (FSR) sensor, the exoskeleton actively assists in walking. Simultaneously, it also triggers the FES of the soleus, tibialis anterior, and gastrocnemius muscles for dorsilflexion and plantar flexion. Later, three different control strategies are employed for the pulse-width controlled FES. Eventually, an ILC with a PID controller is applied in the hybrid exoskeleton, following the best foot angle trajectory.

The research on the effect of neuromuscular electrical stimulation (NMES) protocol on skin temperature (Tsk) in individuals with spinal cord injury (SCI) is a prospective non-controlled intervention study. 47 individuals with SCI were recruited from the outpatient clinic. NMES was applied to the tibial anterior (TA) muscles. Four assessments were performed: baseline, shortly after the end of NMES session (t0), 10 min after the end of NMES (t10) and 20 min after the end of NMES (t20). The intensity used was 1.5 mA RMS (root mean square) depending on the individuals. The variables were Tsk at forehead, dermatome C2 and L5 bilaterally. The dermatome C2 and forehead were measured only at baseline and t20. The measurement device was a noncontact infrared thermometer. Results of this study demonstrated that after NMES the stimulated dermatome (L5), showed an increase in local Tsk. In addition, the t20 showed that the Tsk did not drop to the baseline, being still significant in the analyzed group. The implications for rehabilitation practice and the positive effects of NMES are fundamental to improvement of the blood microcirculation and local metabolism.

This research assesses the effect of tibial nerve electrical stimulation on urinary incontinence in individuals with spinal cord injury (SCI) being a prospective noncontrolled intervention study. 8 individuals with SCI were recruited from the outpatient clinic. This study demonstrates results of tibial nerve stimulation (TNS) applied to the tibial nerves for 12 weeks. Two questionnaires were applied (Neurogenic Bladder Symptom Score-NBSS and Qualiveen- SF) and presented a tendency to improve symptoms and quality of life, however, without statistical significance. With the urodynamic data: maximum cystometric capacity increased with a mean of 285.6 ml pre, to 314.8 ml post TNS (P-Value: 0.554); compliance increased from 26.38ml/cmH2O pre TNS to 29.88ml/cmH2O post TNS (PValue: 0.461); detrusor hyperactivity in the filling phase occurred in all patients in the pre TNS assessment; the maximum amplitude of the detrusor pressure in mean detrusor overactivity after TNS increased from 62.0 to 66.6 cmH2 (PValue: 0.674); urinary leakage pressure during detrusor overactivity pre TNS were mean of 54.0 and 53.2 after (PValue: 1). The implications for rehabilitation practice and the positive effects of TNS are fundamental to improving the quality of life and reducing urinary incontinence on these individuals. Clinical outcomes, i.e., improvement on urinary incontinence can be achieved within a short period of intervention.

When using functional electrical stimulation (FES) for cycling in individuals with spinal cord injury (SCI) during FES-cycling, a rapid onset of muscular fatigue can be observed. Among other reasons, missing neural feedback from the lower extremities might be responsible for a reduced sympathetic response during stimulation. Therefore, this project explores different methods to activate the sympathetic nervous system to increase the heart rate to allow better blood circulation and oxygenation in the working muscles. Six techniques were selected to be tested on 10 healthy participants in the context of pilot measurements. Those were the cold pressor test with both hands, a virtual reality roller-coaster ride, the hot water immersion test with two hands, the Wim Hof breathing method, the Valsalva manoeuvre and the ingestion of Capsaicin through Prik Jinda chilli peppers. The results showed a significant increase in average as well as peak heart rate during all methods performed. From baselines of around 68±1.3 bpm, the strongest increases in both parameters were found for the Valsalva manoeuvre (to 118±20.9 bpm peak, 91±14.2 bpm average), the Wim Hof breathing method (to 112±13.5 bpm peak, 86±11.8 bpm average) and Capsaicin ingestion (to 103±18.9 bpm peak, 80±16.7 bpm average). The methods as they were performed in this project, are not all directly applicable to FES-Cycling but rather serve as exploration how efficiently which stimuli can increase the heart rate. In future research, adaptation or combination of techniques might help to increase performance during FES-Cycling.

Electrical stimulation is a tool that has been used in various ways in the rehabilitation of spinal cord injuries. Surface i.e. electromyography is an effective method for assessing the many conditions in which the patient is. Objective: To evaluate the benefits through neuromuscular electrostimulation in patients with spinal cord injury and possible neuroplasticity gain observed in electromyography. Method: This is a pilot study on the evolution of clinical cases of different neurological levels of spinal cord injury. Conclusion: It was observed that the spinal cord injured patients analyzed in this preliminary study showed possible gain in neuroplasticity.

Introduction: The results of two spiroergometric measurements are presented that were taken from a spinal cord injured patient who participated in FES cycling training sessions for 11 months. Methods: The two measurements were taken 4 and 11 months after starting the training program. We investigated the respiratory exchange ratio (RER) and ventilation (VE/VO2, VE’/VCO2) ratios and the cycling cadence in the two investigated training sessions. Results: In the first assessment, the RER was below 1, which is the anaerobic training limit. Seven months later, in the second assessment, the RER value exceeded the anaerobic limit a few times and remained above it at the end of the session. The VE /VO2 and VE/VCO2 curves did not intersect during the first assessment. In the second one, the VE/VO2 and VE/VCO2 curves intersected several times and the oxygen quotient curve exceeded the carbon dioxide quotient curve. The patient achieved a low but similar cycling speed during the two assessments. Conclusion: Through the activation of paralyzed muscles with FES cycling we are able to train the paraplegic patient in aerobic and anaerobic training zones. This is shown by the value of RER, which reached the anaerobic training limit during the second assessment and remained in the anaerobic range for longer time.

Stimulation of axons or its avoidance plays a central role for neuroprosthetics and neural-interfaces research. One peculiar example constitutes retinal implants. Retinal implants aim to artificially activate retinal ganglion cells (RGCs) via electrical stimulation. Such stimulation, however, often generates undesired stimulation of RGC axon bundles, which leads to distorted visual percepts. In order to establish stimulation strategies avoiding axonal stimulation it is necessary to image the evoked activity in single axons. In this work we electrically imaged axonal stimulation in ex vivo mouse retina using a high-density CMOS-based microelectrode array. We demonstrate signal propagation tracking via stimulus triggered average during high frequency (100 Hz) sinusoidal electrical stimulation.

Introduction : Despite its central role in medicine electrical stimulation (ES) is still limited by its selectivity. Different reports did assess effects of different waveforms, intensities, and frequency on the activation threshold of nerve fibres with different diameters. We aimed to extend this knowledge by investigating the effect of short monophasic rectangular pulses (1, 2, 5, 10, 50, 100 and 200 μs) on the recruitment order. Methods: The sciatic nerve of rats was stimulated, and the evoked compound nerve action potential (CNAP) measured at two sites on the tibialis nerve, using epineural electrodes. Changes in delay, amplitude, and the shape of the CNAP were analyzed. Results: The amplitude and delay of the CNAP were significantly affected by the pulse-width (PW). The delay and duration of the compound nerve action potential increased with longer PW, while the amplitude decreased. Discussion: Found changes are likely caused by changes in the time point of excitation of individual neuron fibres, depending on electrical field strength and exposure time. This might be of particular interest when selecting PWs for design and validation of stimulation patterns and analysis of experimental and clinical observations.

According to the Neuro Patience report of the Neurological Alliance, 1 in 6 people in the UK has a neurological condition. With the growth in technology, rehabilitation for neurological problems is one of the fastgrowing fields. Functional Electrical Stimulation (FES) is one of those neuro-rehabilitation methods that uses electrical nerve stimulation to restore functional muscle movements that are lost due to neurological problems such as stroke and multiple sclerosis. This neuroprosthetic device is frequently used to assist walking by treating a condition called Drop Foot, a result of paralysis of the pretibial muscles. This study proposes a two-channel FES device called the SmartStim, which has the ability to modulate its stimulation levels according to various obstacles such as stairs and ramps. This system employs a sensor-based module with a Recurrent Neural Network to classify these different walking scenarios. The module is built with Inertial Measurement sensors embedded in a pair of shoes, and the Recurrent Neural Network uses data from these sensors to predict various obstacles as the user is walking. These predictions are then used by a Fuzzy Logic Controller to control and regulate the stimulation current in two channels of the SmartStim system. In the two channels of the system, one channel will help aid with drop foot, while the other will be used to stimulate another muscle group to help access stairs and ramps by the user. The Recurrent Neural Network module in this system has been trained and tested using the k-fold cross-validation. The evaluation of this trained model shows that it can predict obstacles from sensor data at 97 percent accuracy. Currently, further testing is being performed to assess the workings of the fuzzy logic controller in combination with the Recurrent Neural Network in healthy individuals. It is expected that the SmartStim system may aid users in accessing various walking scenarios more efficiently.