Transcutaneous Nerve Bundle Stimulation for Dexterous Hand Grasp Patterns: Development and Exploration of an Alternative Stimulation Method

Impairment of the hand following a neurological injury such as stroke is a major contributing factor to the loss of independence and self-sufficiency. Neuromuscular Electrical Stimulation (NMES) is a widely utilized technique to help alleviate lost muscle strength by electrically eliciting muscle contractions. However, conventional NMES applied directly over the muscle belly often faces various limitations, which prevent long-term use and efficacy. Traditional NMES techniques induce rapid muscle fatigue due to non-physiological activation of fibers resulting in a decline of muscle force. For the hand, stimulation at the skin surface typically only activates the superficial extrinsic hand muscles, leading to limited multi-joint control. To overcome these limitations, we sought to develop an alternative stimulation technique that used a high-density surface electrode array to directly target major nerve bundles at a location more proximal to the muscles. First, we designed an automated stimulation paradigm to characterize the different patterns of finger flexion elicitable via the nerve stimulation method. Randomized pairs in the electrode array were used to search for the best stimulation locations. We demonstrated that the nerve stimulation can generate a variety of single and multi-finger flexion patterns, with selective sets of nerve fiber activation and high activation redundancy. Secondly, we compared the force sustainability of the proximal nerve stimulation with conventional muscle belly stimulation. We found that, with prolonged force-matched stimulations, the proximal nerve stimulation technique can significantly delay the decline of force production over time, which allowed us to elicit sustained muscle force output. Lastly, we investigated the ability of the proximal nerve stimulation to activate both the superficial and deep extrinsic finger flexors. We obtained ultrasound images of the cross section of the flexor muscles in the forearm, and image deformation was used as a surrogate measure of muscle contraction. We found that superficial and deep muscles could be separately or concurrently activated. Overall, this work demonstrated the appealing features of our nerve stimulation method in selectively recruiting different finger flexor muscles with sustained activation. The outcomes also lay the theoretical foundation for further development of proximal nerve stimulation as an alternative approach for effective hand rehabilitation.Doctor of Philosoph

Electrocutaneous stimulation to close the loop in myoelectric prosthesis control

Current commercially available prosthetic systems still lack sensory feedback and amputees are forced to maintain eye-contact with the prosthesis when interacting with their environment. Electrocutaneous stimulation is a promising approach to convey sensory feedback via the skin. However, when discussed in the context of prosthetic applications, it is often refused due to its supposed incompatibility with myocontrol. This dissertation now addresses electrocutaneous stimulation as means to provide sensory feedback to prosthesis users, and its implications on myoelectric control, possible use for improved or accelerated mastering of prosthesis control through closing of the control loop, as well as its potential in aiding in the embodiment of prosthetic components. First, a comparison of different paradigms for encoding sensory feedback variables in electrocutaneous stimulation patterns was done. For this, subject ability to employ spatially and intensity-coded electrocutaneous feedback in a simulated closed-loop control task was evaluated. The task was to stabilise an invisible virtual inverted pendulum under ideal feedforward control conditions (joystick). Pendulum inclination was either presented spatially (12 stimulation sites), encoded by stimulation strength (≧ 2 stimulation sites), or a combination of the two. The tests indicated that spatial encoding was perceived as more intuitive, but intensity encoding yielded better performance and lower energy expenditure. The second study investigated the detrimental influence of stimulation artefacts on myoelectric control of prostheses for a wide range of stimulation parameters and two prosthesis control approaches (pattern recognition of eight motion primitives, direct proportional control). Artefact blanking is introduced and discussed as a practical approach to handle stimulation artefacts and restore control performance back to the baseline. This was shown with virtual and applied artefact blanking (pattern recognition on six electromyographic channels), as well as in a practical task-related test with a real prosthesis (proportional control). The information transfer of sensory feedback necessary to master a routine grasping task using electromyographic control of a prosthesis was investigated in another study. Subjects controlled a real prosthesis to repeatedly grasp a dummy object, which implemented two different objects with previously unknown slip and fragility properties. Three feedback conditions (basic feedback on grasp success, visual grasp force feedback, tactile grasp force feedback) were compared with regard to their influence on subjects’ task performance and variability in exerted grasp force. It was found that online force feedback via a visual or tactile channel did not add significant advantages, and that basic feedback was sufficient and was employed by subjects to improve both performance and force variability with time. Importantly, there was no adverse effect of the additional feedback, either. This has important implications for other non-functional applications of sensory feedback, such as facilitation of embodiment of prosthetic devices. The final study investigated the impact of electrocutaneous stimulation on embodiment of an artificial limb. For this purpose, a sensor finger was employed in a rubber-hand-illusion-like experiment. Two independent groups (test, control), were compared with regard to two objective measures of embodiment: proprioceptive drift, and change in skin temperature. Though proprioceptive drift measures did not reveal differences between conditions, they indicated trends generally associated to a successful illusion. Additionally, significant changes in skin temperature between test and control group indicated that embodiment of the artificial digit could be induced by providing sensory substitution feedback on the forearm. In conclusion, it has been shown that humans can employ electrocutaneous stimulation feedback in challenging closed-loop control tasks. It was found that transition from simple intuitive encodings (spatial) to those providing better resolution (intensity) further improves feedback exploitation. Blanking and segmentation approaches facilitate simultaneous application of electrocutaneous stimulation and electromyographic control of prostheses, using both pattern recognition and classic proportional approaches. While it was found that force feedback may not aid in the mastering of routine grasping, the presence of the feedback was also found to not impede the user performance. This is an important implication for the application of feedback for non-functional purposes, such as facilitation of embodiment. Regarding this, it was shown that providing sensory feedback via electrocutaneous stimulation did indeed promote embodiment of an artificial finger, even if the feedback was applied to the forearm. Based on the results of this work, the next step should be integration of sensory feedback into commercial devices, so that all amputees can benefit from its advantages. Electrocutaneous stimulation has been shown to be an ideal means for realising this. Hitherto existing concerns about the compatibility of electrocutaneous stimulation and myocontrol could be resolved by presenting appropriate methods to deal with stimulation artefacts

Rehabilitation Engineering

Population ageing has major consequences and implications in all areas of our daily life as well as other important aspects, such as economic growth, savings, investment and consumption, labour markets, pensions, property and care from one generation to another. Additionally, health and related care, family composition and life-style, housing and migration are also affected. Given the rapid increase in the aging of the population and the further increase that is expected in the coming years, an important problem that has to be faced is the corresponding increase in chronic illness, disabilities, and loss of functional independence endemic to the elderly (WHO 2008). For this reason, novel methods of rehabilitation and care management are urgently needed. This book covers many rehabilitation support systems and robots developed for upper limbs, lower limbs as well as visually impaired condition. Other than upper limbs, the lower limb research works are also discussed like motorized foot rest for electric powered wheelchair and standing assistance device