Chris FreemanControl System Design for Electrical Stimulation in Upper Limb Rehabilitation10.1007/978-3-319-25706-8_1

1. Introduction

Chris Freeman¹

(1)

University of Southampton, Southampton, UK

Chris Freeman

Fifteen million people annually experience a stroke, and every two seconds someone in the world will have a stroke for the first time [1]. During a stroke, tissues in the brain are damaged because their blood supply is obstructed by a blood clot or by a narrowing or bursting of blood vessels. A third of people who experience a stroke are left permanently disabled, and require care. Since stroke is an age-related disease, the number of strokes worldwide is expected to increase. The burden of stroke is often measured using disability-adjusted life years (DALYs), which combine years of potential life lost due to premature death with years of productive life lost due to disability. Using this measure, stroke burden is projected to rise from 38 million DALYs globally in 1990 to 61 million DALYs in 2020.

A common result of stroke is an impaired ability to control movement. For example, half of all acute stroke patients starting rehabilitation have a marked impairment of function of one arm, of whom only about 14 % will regain sensory-motor function. This is particularly detrimental since it has also been argued that arm and hand function is more important than mobility in achieving independence after stroke.

The brain’s ability to reorganize itself by forming new neural connections means that it is possible to ‘re-learn’ lost movement capability through intense practice of functional tasks. As with learning any new skill, this process requires sensory feedback (e.g. visual, proprioceptive or haptic) to promote the necessary reorganization of pathways in the motor cortex of the brain. The problem facing the stroke patient is that they are unable to practice moving their impaired limb and therefore are unable to receive feedback. The longer this disuse continues, the less likely recovery becomes because surrounding areas of the motor cortex are gradually taken over by other functions still under the patient’s voluntary control.

1.1 Rehabilitation Technologies

Conventional therapy consists of performing movement exercises using the impaired arm, with assistance provided by a physiotherapist. Unfortunately, conventional treatments have been found to have a very limited effect on recovery of useful function, and there is hence a pressing need for novel rehabilitation technologies to support recovery of arm function post-stroke. Governments around the world are urging health and social care services to adopt innovative technology that patients can use at home to support independent living. For example, the UK government termed the situation a ‘ticking time bomb’ in a recent report, and in 2014 introduced the ‘Care Bill’ calling on health and social services to adopt innovative technology that patients can use at home to support independent living.

In recent years new assistive technologies have emerged to reduce impairment post-stroke, including electrical stimulation [2–5] and rehabilitation robots [6], which facilitate intense practice of movement in a motivating environment. These technologies have potential to provide the motivation, assistance, range and duration of task practice required for effective rehabilitation of functional movement.

Electrical stimulation (ES) uses electric impulses to artificially contract muscles and has become an area of intense engineering and clinical research over the last few years. By directly activating weak or paralyzed muscles, ES is able to drive neuroplastic cortical changes to enable recovery. ES is supported by a growing body of clinical evidence [7–9]. For example, meta-analysis of 22 randomized control trials involving 894 participants in [8] found that neuromuscular stimulation of the wrist/finger flexors/extensors had a significant beneficial effect on motor function (impairment) and muscle strength. This body of clinical evidence has theoretical support from neurophysiology [10] and motor learning [11] which shows that the therapeutic benefit increases when it is applied co-incidently with a patient’s own voluntary intention [12]. Hence ES must precisely assist the patient’s own voluntary task completion in order to maximize functional recovery. Its inherent affordability means there is also intense commercial interest in ES technology, with numerous products available on the market. Use of ES has also gained recognition from bodies such as The Royal College of Physicians (RCP), National Institute for Health and Care Excellence (NICE), and Evidence-Based Review of Stroke Rehabilitation (EBRSR). The latter concludes that ‘there is strong evidence that ES treatment improves upper extremity function’.

Increasingly ES is being combined with mechanical support, taking the form of either passive orthoses or active robots. These devices help support the affected limb, and may resist or assist movement through various training modalities. They can therefore help reduce muscle fatigue or provide functionality that ES cannot (e.g. to assist with forearm supination or help stabilze the scapula).

Although systematic reviews support the use of robots [13] and electrical stimulation [8, 9] to reduce impairments and in some cases improve function, translation into clinical practice remains poor. A recent survey has found that removal of key barriers limiting translation requires improvements in assistive technology design, pragmatic clinical evaluation, better knowledge and awareness and improvement in provision of services [14].

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