It has been my pleasure and happiness to learn from the top-notch rehabilitation robotics staff at Vanderbilt University. Clonus from wheelchair inertia is about a quarter of the force of clonus inertia at the legs.
INTRODUCTION
The Brain and Injury
- The Central Nervous System
- The Spinal Cord
- The Peripheral Nervous System
- Spinal Reflexes
The spinal cord also transmits afferent signals from sensory fibers of the peripheral nervous system (PNS). The myelinated axons of these pathways form the white matter of the spinal cord.
Spinal Cord Injury
- Spasticity
- Neurorehabilitation
The induced current field depends on the artificial stimulation and is controlled by the system (stimulator parameters, electrodes and electrode position). One of the biggest hurdles to overcome in exoskeleton research is user interface and control.
Summary of Contributions
- Stair Climbing
- Exoskeleton Gait Training and Spasticity
- Wheelchair Propulsion and Spasticity
The stimulation was timed with the swing phase of the exoskeleton and is intended to reduce extension spasticity by recruiting the flexion-withdrawal reflex. Clonus of the ankle can manifest during wheelchair propulsion when the terrain causes afferent activation either via proprioceptors or exteroceptors.
HARDWARE
Indego Exoskeleton
The previous SCI Indega controller performs motor control by following predetermined joint angle trajectories. Although the Vanderbilt exoskeleton suffered fractures, burns, electric shocks, etc., the Indego research prototypes proved to be robust, reliable and capable exoskeletons.
Chimera Stimulation Board
Another potential danger is the implementation of an unbalanced charge to the patient, which can cause electrolysis of the tissue. The application enabled wireless interfacing with the device and unlocked the expansive potential of the Chimera hardware for wearable use.
1 - VARIABLE GEOMETRY STAIR ASCENT AND DESCENT
- Abstract
- Introduction
- Controller
- Joint-level Controllers
- Ascent Supervisory Controller
- Descent Supervisory Controller
- Assessment Method
- Results
- Stair Ascent Results
- Stair Descent Results
- Other Results
- Discussion
- Conclusion
The work presented here specifically describes a stair ascent and descent controller to enable variable geometry stair ascent and descent with a lower limb exoskeleton, and experimentally characterizes the functionality of the exoskeleton by doing so on three motor-complete subjects. 33 trajectory to return the exoskeleton to the standing position in state 1 (although placed one step below the previous cycle). Step time (ie, the time required to ascend or descend a single flight of stairs) is determined by the trajectory speed and the user's ability to trigger the step sequence.
It should be noted that the healthy stair ascent and descent data correspond to a step-over-aisle, while the exoskeleton provides a step-to-aisle. 44 As observed in the first row of the table, ascending and descending with the exoskeleton is significantly slower than healthy walking. Considering the joint mean "torque effort", the exoskeleton provides 0.67 Nm/kg while healthy subjects are characterized by 0.9 Nm/kg.
Specifically, the exoskeleton delivers peak joint torques averaging 110% and 74% of the corresponding healthy peak joint torques during ascent and descent, respectively, and peak joint powers averaging 63%.
MANUSCRIPT 2 - SUPPLEMENTAL STIMULATION IMPROVES SWING PHASE
- Abstract
- Introduction
- Methods
- Clinical Status
- Stimulator
- Hybrid Controller
- Experimental Procedure
- Results
- Discussion
- Conclusion
Severe extensor spasticity, in particular, can preclude hip and knee flexion during the movement phase of walking, greatly negating the ability of the exoskeleton to provide effective leg mobility. That study specifically paired a lower limb exoskeleton with FES of the quadriceps and hamstring muscle groups of each leg, and showed reduced exoskeleton motor torque and power when used in a hybrid FES mode. To do this, the authors propose here to supplement an exoskeleton with stimulation of the common peroneal nerve with the aim of stimulating the flexion-withdrawal reflex.
To evaluate this hypothesis, a lower limb exoskeleton system was configured to include supplemental FES from the common peroneal nerve, and experiments were performed on two SCI subjects with severe extensor spasticity to determine the effect of supplemental peroneal stimulation on exoskeleton-generated swing phase to evaluate movement. This study was conducted with the informed consent of each subject and with the approval of the Vanderbilt University Internal Review Board. 56 In addition, FES has been shown to offer therapeutic value for persons with SCI by activating the dormant neuromuscular tissue of the paralyzed limbs.
In two thoracic level SCI subjects with severe extensor spasticity of the lower limbs, supplemental stimulation of the common peroneal nerve was shown to significantly increase the walking motion generated by the exoskeleton and significantly reduce the current demand on the exoskeleton motors.
CLONUS ATTENUATOR EVALUATION
Abstract
Introduction
These lower the excitability of the stretch reflex with effects that can vary from ineffective to effects that carry over a day [119]. This focal treatment acts on the axon ends of the neuromuscular junction and prevents the neurotransmitter acetylcholine from activating the muscle. FES of the peroneal nerve has been attributed to long-term reduction in tone and phasic spasticity for hemiparesis.
The anti-clonus model treats clonic triceps surea via stimulation of the peroneal nerve for the monosynaptic reflex that results in a mild tonic contraction of the tibialis anterior and reciprocal inhibition of the triceps surea [21]. Dimitrijevic indicates that although efficacy is dependent on the frequency of the stimulation pulses, the method is robust to the temporal variability of excitability, and has a potentially beneficial long-term potentiation of clonus suppression. Although Dimitrijevic suggests that this model is suitable for a device that uses a myoelectric or electromechanical sensor to detect clonus and the stimulation to suppress clonus, no literature, sales, or publication of such a device has been found that would demonstrate the efficacy of the anti-clonus model validates.
This method provides a controlled study paradigm for repeated clonus onset in an attempt to observe the temporal response to repeated anti-clonus stimulation for a heterogeneous population sample of users.
Methods
- Overview
- Controller
- Over-ground Study
- Benchtop Study
- Subject Evaluation
63 The adaptation sub-machine (Fig. 5-3) of the clonus state adapts both the anticlonus and inhibitory stimulation amplitudes. If the clonus state is re-entered within a predetermined time (eg, 6 s), the preventive stimulation is increased (eg, 2 mA); Alternatively, if a prolonged period passes without clonus, preventive stimulation may decrease. The data were then used to evaluate the performance of the anti-clonus intervention compared to the control sub-trial.
The bandwidth of the system is limited to the Nyquist frequency of 50 Hz at the sampling rate of 100 Hz. Footage from the trials was used to quantify the duration of clonus and foot-off during each trial. Visual analysis was used to evaluate the ability of the Chimera to prevent clonus and displace the foot from the footrest.
Characterization of the short-term response to anti-clonus controller was performed by repeatedly initiating and suppressing clonus with the anti-clonus controller and device.
Results
- Over-ground Results
- Subject Evaluation Results
The percent pathology difference is the percent difference of the sums of clonus and foot-off (pathologies) of the control and intervention sub-trials. This measure summarizes the effectiveness of the anti-clonus intervention for the treatment of pathological clonus during wheelchair mobility over rough terrain. Ten of the eleven trials saw a decrease in spasticity as a result of activating the FES controller.
The mean amplitudes of clonus and preemptive stimulation were normalized to the maximum value set at the beginning of the experimental session. The prevention and clonu prevalence (%) are the percentage of the sub-trial spent in the corresponding state. In addition, mean FES statistics for both legs are reported for the intervention subtrial: mean active stimulation amplitude during the clonus and rough terrain conditions (AC amplitude and Preventive Amp.) and the prevalence of the rough terrain and clonus conditions.
Increased tolerance to the withdrawal reflex may be due to accommodation or habituation (see discussion).
Discussion
Results from the subject evaluations, shown in Table 5-5, describe some physiological changes that may result from the intervention or propulsion above ground. Short-term and long-term habituation is dependent on the interval of stimulus application and probably acts on interneurons involved in the flexion reflex ([9] p. 1250). This narrow bandpass significantly attenuates the amplitude of the signals caused by traversing rough terrain; the chair clonus signal (shown in Figs. 5-11 and 5-12) remains well within the clonus threshold while traversing rough terrain.
The clonus and terrain signals can be compared by signal to noise ratio (SNR), where the signal is the root mean square of the signal value during the clonus condition, while the noise is the root mean square of the signal value in the rough. - terrain condition. These results validate the value of the bandpass filter for processing the clonus signal from bone data from all the experiments. Not found" column; therefore, the activity in the clonus frequency of 5 Hz, but this perturbation has much less significant effect, about one fifth of the effect of the clonus-detected spectral analysis.
Fast-Fourier transform (FFT) of the leg raw IMU data during the controller-detected clonus condition reveals the strength of the characteristic clonus frequency in the leg acceleration data, see Fig.
Conclusion
Clinical testing with a variety of subjects with spinal cord injury allowed evaluation of the prototyped interventions. Fife, “Effects of functional electrical stimulation on the joints of adolescents with spinal cord injury,” Paraplegia, vol. Kunkel, “EFFECTS OF FUNCTIONAL ELECTRICAL STIMULATION-INDUCED CYCLING OF THE LOWER EXTREMITIES ON BONE DENSITY OF PATIENTS WITH DRUBBER GENERAL SYSTEM1,” Am.
Stüssi, “Effect of electrical stimulation-induced cycling on bone mineral density in spinal cord injured patients,” Eur. Chen, “Bone mineral density increase after functional electrical stimulation cycling exercise in spinal cord injured patients,” Disabil. Brissot et al., “Clinical experience with functional electrical stimulation-assisted walking with the Parastep in spinal cord-injured patients,” Spine, vol.
Lavrač, "Use of functional electrical stimulation in the lower limbs of incomplete spinal cord injured patients," Artif. Singleton, “A clinically significant training effect in walking speed using functional electrical stimulation for motor incomplete spinal cord injury.,” J. Sawatzky, “Static standing, dynamic standing, and spasticity in individuals with spinal cord injury,” Spinal Cord, vol.
![Table 3-1: Exoskeleton and healthy stair ascent and descent characteristics. Healthy data from [1]](https://thumb-ap.123doks.com/thumbv2/123dok/10740082.0/54.918.114.834.865.1079/table-exoskeleton-healthy-stair-ascent-descent-characteristics-healthy.webp)
