Antonio J. del-Ama

Review of Hybrid Exoskeletons to Restore Gait Following Spinal Cord Injury

Different approaches are available to compensate gait in persons with spinal cord injury, including passive orthoses, functional electrical stimulation (FES), and robotic exoskeletons. However, several drawbacks arise from each specific approach. Orthotic gait is energy-demanding for the user and functionally ineffective. FES uses the muscles as natural actuators to generate gait, providing not only functional but also psychological benefits to the users. However, disadvantages are also related to the early appearance of muscle fatigue and the control of joint trajectories. Robotic exoskeletons that provide joint moment compensation or substitution to the body during walking have been developed in recent years. Significant advances have been achieved, but the technology itself is not mature yet because of many limitations related to both physical and cognitive interaction as well as portability and energy-management issues. Meanwhile, the combination of FES technology and exoskeletons has emerged as a promising approach to both gait compensation and rehabilitation, bringing together technologies, methods, and rehabilitation principles that can overcome the drawbacks of each individual approach. This article presents an overview of hybrid lower-limb exoskeletons, related technologies, and advances in actuation and control systems. Also, we highlight the functional assessment of individuals with spinal cord injury.

Hybrid FES-robot cooperative control of ambulatory gait rehabilitation exoskeleton

AbstractRobotic and functional electrical stimulation (FES) approaches are used for rehabilitation of walking impairment of spinal cord injured individuals. Although devices are commercially available, there are still issues that remain to be solved. Control of hybrid exoskeletons aims at blending robotic exoskeletons and electrical stimulation to overcome the drawbacks of each approach while preserving their advantages. Hybrid actuation and control have a considerable potential for walking rehabilitation but there is a need of novel control strategies of hybrid systems that adequately manage the balance between FES and robotic controllers. Combination of FES and robotic control is a challenging issue, due to the non-linear behavior of muscle under stimulation and the lack of developments in the field of hybrid control. In this article, a cooperative control strategy of a hybrid exoskeleton is presented. This strategy is designed to overcome the main disadvantages of muscular stimulation: electromechanical delay and change in muscle performance over time, and to balance muscular and robotic actuation during walking.Experimental results in healthy subjects show the ability of the hybrid FES-robot cooperative control to balance power contribution between exoskeleton and muscle stimulation. The robotic exoskeleton decreases assistance while adequate knee kinematics are guaranteed. A new technique to monitor muscle performance is employed, which allows to estimate muscle fatigue and implement muscle fatigue management strategies. Kinesis is therefore the first ambulatory hybrid exoskeleton that can effectively balance robotic and FES actuation during walking. This represents a new opportunity to implement new rehabilitation interventions to induce locomotor activity in patients with paraplegia.Acronym list: 10mWT: ten meters walking test; 6MWT: six minutes walking test; FSM: finite-state machine; t-FSM: time-domain FSM; c-FSM: cycle-domain FSM; FES: functional electrical stimulation; HKAFO: hip-knee-ankle-foot orthosis; ILC: iterative error-based learning control; MFE: muscle fatigue estimator; NILC: Normalized stimulation output from ILC controller; PID: Proportional-Integral-derivative Control; PW: Stimulation pulse width; QUEST: Quebec User Evaluation of Satisfaction with assistive Technology; SCI: Spinal cord injury; TTI: torque-time integral; VAS: Visual Analog Scale.

Control of an ambulatory exoskeleton with a brain-machine interface for spinal cord injury gait rehabilitation

The closed-loop control of rehabilitative technologies by neural commands has shown a great potential to improve motor recovery in patients suffering from paralysis. Brain–machine interfaces (BMI) can be used as a natural control method for such technologies. BMI provides a continuous association between the brain activity and peripheral stimulation, with the potential to induce plastic changes in the nervous system. Paraplegic patients, and especially the ones with incomplete injuries, constitute a potential target population to be rehabilitated with brain-controlled robotic systems, as they may improve their gait function after the reinforcement of their spared intact neural pathways. This paper proposes a closed-loop BMI system to control an ambulatory exoskeleton—without any weight or balance support—for gait rehabilitation of incomplete spinal cord injury (SCI) patients. The integrated system was validated with three healthy subjects, and its viability in a clinical scenario was tested with four SCI patients. Using a cue-guided paradigm, the electroencephalographic signals of the subjects were used to decode their gait intention and to trigger the movements of the exoskeleton. We designed a protocol with a special emphasis on safety, as patients with poor balance were required to stand and walk. We continuously monitored their fatigue and exertion level, and conducted usability and user-satisfaction tests after the experiments. The results show that, for the three healthy subjects, 84.44 ± 14.56% of the trials were correctly decoded. Three out of four patients performed at least one successful BMI session, with an average performance of 77.6 1 ± 14.72%. The shared control strategy implemented (i.e., the exoskeleton could only move during specific periods of time) was effective in preventing unexpected movements during periods in which patients were asked to relax. On average, 55.22 ± 16.69% and 40.45 ± 16.98% of the trials (for healthy subjects and patients, respectively) would have suffered from unexpected activations (i.e., false positives) without the proposed control strategy. All the patients showed low exertion and fatigue levels during the performance of the experiments. This paper constitutes a proof-of-concept study to validate the feasibility of a BMI to control an ambulatory exoskeleton by patients with incomplete paraplegia (i.e., patients with good prognosis for gait rehabilitation).

Online Assessment of Human-Robot Interaction for Hybrid Control of Walking

Restoration of walking ability of Spinal Cord Injury subjects can be achieved by different approaches, as the use of robotic exoskeletons or electrical stimulation of the user’s muscles. The combined (hybrid) approach has the potential to provide a solution to the drawback of each approach. Specific challenges must be addressed with specific sensory systems and control strategies. In this paper we present a system and a procedure to estimate muscle fatigue from online physical interaction assessment to provide hybrid control of walking, regarding the performances of the muscles under stimulation.

Benchmarking Bipedal Locomotion: A Unified Scheme for Humanoids, Wearable Robots, and Humans

In the field of robotics, there is a growing awareness of the importance of benchmarking [1], [2]. Benchmarking not only allows the assessment and comparison of the performance of different technologies but also defines and supports the standardization and regulation processes during their introduction to the market. Its importance has been recently emphasized by the adoption of the technology readiness levels (TRLs) in the Horizon 2020 information and communication technologies by the European Union as an important guideline to assess when a technology can shift from one TRL to the other. The objective of this article is to define the basis of a benchmarking scheme for the assessment of bipedal locomotion that could be applied and shared across different research communities.

Hybrid gait training with an overground robot for people with incomplete spinal cord injury: a pilot study

Locomotor training has proved to provide beneficial effect in terms of mobility in incomplete paraplegic patients. Neuroprosthetic technology can contribute to increase the efficacy of a training paradigm in the promotion of a locomotor pattern. Robotic exoskeletons can be used to manage the unavoidable loss of performance of artificially driven muscles. Hybrid exoskeletons blend complementary robotic and neuro-prosthetic technologies. The aim of this pilot study was to determine the effects of hybrid gait training in three case studies with persons with incomplete spinal cord injury (iSCI) in terms of locomotion performance during assisted gait, patient-robot adaptations, impact on ambulation and assessment of lower limb muscle strength and spasticity. Participants with iSCI received interventions with a hybrid bilateral exoskeleton for 4 days. Assessment of gait function revealed that patients improved the 6 min and 10 m walking tests after the intervention, and further improvements were observed 1 week after the intervention. Muscle examination revealed improvements in knee and hip sagittal muscle balance scores and decreased score in ankle extensor balance. It is concluded that improvements in biomechanical function of the knee joint after the tested overground hybrid gait trainer are coherent with improvements in gait performance.

Hybrid therapy of walking with Kinesis overground robot for persons with incomplete spinal cord injury

Rehabilitation of walking ability is one of the most important objectives after a spinal cord injury. Robotic and neuroprosthetic technologies hold a considerable potential for driving walking rehabilitation therapies. However, new developments are needed in order to improve the walking rehabilitation interventions based in these technologies.We recently presented a cooperative control strategy of Kinesis, a lower limb exoskeleton for providing hybrid therapy of walking (Del-Ama, 2014). Its design aimed to actively manage muscle fatigue caused by surface electrical stimulation, and to implement the assist-as-needed control paradigm in which both stimulation and robotic controller cooperate with the residual functionality of the user. In this article we present three case studies for investigating the feasibility of the hybrid therapy of walking delivered with Kinesis in patients with incomplete spinal cord injury. Besides, the adaptability features of Kinesis stimulation-robot cooperative control are assessed, characterizing the behavior of the cooperative controller while providing hybrid therapy of walking.Patients with incomplete spinal cord injury participated in the experiments. The protocol consisted of walking with Kinesis during 6?min. Three configurations of the cooperative controller were tested for each patient in separate sessions in order to investigate its adaptability features. The immediate impact of the hybrid therapy of walking was assessed through several variables that represent the physiological impact, user-exoskeleton physical interaction, stimulation intensity and user subjective perception of the hybrid therapy of walking.Results show that the cooperative controller of Kinesis adapted to patient functional deficits and voluntary actions during walking, modulating stimulation and robotic assistance, which was the aim of the controller design. Nevertheless, no noticeable differences were observed in the comparison between compliant and trajectory exoskeleton control. Further work is envisioned regarding several aspects of hybrid walking control: stimulation control based on muscle activation estimate, improved semi-automatic control of walking, and improved muscle fatigue monitoring. The hybrid walking therapy was tolerated by the patients without adverse effects, along with a tolerable physical demand. This shows a potential for walking rehabilitation in motor incomplete SCI patients, guaranteeing further research on this topic. We investigate the feasibility of providing the hybrid therapy of walking with Kinesis hybrid exoskeleton.We compare and investigate the role of the stimulation and the compliant robot control.Three case studies are presented. The cooperative controller of Kinesis adapted to patients and voluntary actions.No noticeable differences were observed between compliant and trajectory control.

Decoding the Attentional Demands of Gait through EEG Gamma Band Features

Rehabilitation techniques are evolving focused on improving their performance in terms of duration and level of recovery. Current studies encourage the patient’s involvement in their rehabilitation. Brain-Computer Interfaces are capable of decoding the cognitive state of users to provide feedback to an external device. On this paper, cortical information obtained from the scalp is acquired with the goal of studying the cognitive mechanisms related to the users’ attention to the gait. Data from 10 healthy users and 3 incomplete Spinal Cord Injury patients are acquired during treadmill walking. During gait, users are asked to perform 4 attentional tasks. Data obtained are treated to reduce movement artifacts. Features from δ(1 − 4Hz), θ(4 − 8Hz), α(8 − 12Hz), β(12 − 30Hz), γlow(30 − 50Hz), γhigh(50 − 90Hz) frequency bands are extracted and analyzed to find which ones provide more information related to attention. The selected bands are tested with 5 classifiers to distinguish between tasks. Classification results are also compared with chance levels to evaluate performance. Results show success rates of ∼67% for healthy users and ∼59% for patients. These values are obtained using features from γ band suggesting that the attention mechanisms are related to selective attention mechanisms, meaning that, while the attention on gait decreases the level of attention on the environment and external visual information increases. Linear Discriminant Analysis, K-Nearest Neighbors and Support Vector Machine classifiers provide the best results for all users. Results from patients are slightly lower, but significantly different, than those obtained from healthy users supporting the idea that the patients pay more attention to gait during non-attentional tasks due to the inherent difficulties they have during normal gait. This study provides evidence of the existence of classifiable cortical information related to the attention level on the gait. This fact could allow the development of a real-time system that obtains the attention level during lower limb rehabilitation. This information could be used as feedback to adapt the rehabilitation strategy.

Comparative ergonomic assessment of manual wheelchairs by paraplegic users.

Purpose: The aim of the present study was to describe and test the reliability of a comprehensive product-centered approach to assessing functional performance and wheelchair user perceptions on device ergonomics and satisfaction of performance. A pilot study was implemented using this approach to evaluate differences among four manual wheelchairs. Method:. Six wheelchair users with complete spinal cord injury (SCI) at the thoracic level and with no previous upper limbs impairment were recruited for this study. After finishing circuit tasks, subjects were asked to complete a questionnaire about ergonomic wheelchair characteristics (manoeuvrability, stability, comfort and ease of propulsion) and satisfaction about task performance. On the other hand, objective data were recorded during user performance as the time required to complete each test, kinetic wheelchair propulsion data obtained with two SMARTWheels® and physiological parameters (heart rate and physiological index). Results: Kuschall Champion® and Otto Bock Voyage® wheelchairs were ranked best for most ergonomic aspects specially in manoeuvrability (p < 0.05). Less time was required to execute most of the circuit tasks in both wheelchair models (p < 0.05). Conclusions: This approach proposed highlight the importance of looking both kinds of information, user perception and user functional performance when evaluating a wheelchair or comparing across devices. Implications for Rehabilitation In rehabilitation, the reliability of the clinical evaluation of the wheelchair can help to improve and adapt the wheelchair to patient, contributing significantly to the prevention of overuse injuries in the upper limbs.

Physical activity and transcutaneous oxygen pressure in men with spinal cord injury

This pilot study proposed a method for assessing the status of vascular flow measured by transcutaneous oxygen pressure (TcPO2) in the area of the ischium in people with spinal cord injury (SCI). In a sample of 38 men (two groups: 12 physically active and 26 sedentary) with thoracic SCI, the distribution of the physiological response of the tissues under load during sitting was assessed through analysis of ischium TcPO2 values obtained by an oximeter. TcPO2 baseline, recovery time of TcPO2 after sitting (Trec), the percentage of TcPO2 (%TcPO2) of maximum pressure TcPO2, and mechanic maximal pressure (Pmax) were evaluated. Trec in the physically active group was significantly lower (p < 0.05) than in the sedentary group. Likewise, significant differences in %TcPO2 between groups (p < 0.05) were also found. We concluded that the physiological response of the tissues under an individual with SCIs own weight resulting from prolonged sitting is better in those who are physically active.