Electrical Stimulation - Its role in upper limb recovery post-stroke

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Introduction and Learning Outcomes

Welcome to this online learning resource on the use of functional electrical stimulation (FES) to support recovery of upper limb following a stroke. This interactive learning package has been created by a small group of final year Physiotherapy students from Queen Margaret University as part of the Contemporary and Emerging Issues in Physiotherapy module.

This resource aims:
to provide an interactive learning package for final year students and newly qualified physiotherapists to develop their knowledge and understanding of FES for upper limb recovery following a stroke, and
to provide a resource of key literature and signposting to further reading and content.

Learning Outcomes

The following learning outcomes (LO) have been constructed to support competencies expected of a newly qualified (Band 5) physiotherapist role (ref xxxx). A balance of theory, policy and evidence-base, as well more practical aspects for application of FES has been integrated into the LOs. This choice was based on discussion and feedback with tutors and peers.

By the end of this learning package the user should be able:

LO1: to appraise the guidelines and underpinning literature on the use of FES in stroke upper limb recovery and relate this to your current or future clinical practice setting.

LO2: to discuss the principles, applications and parameters of FES in relation to stroke upper limb recovery.

LO3: to justify the consideration of FES in stroke upper limb assessment and intervention planning.

Layout and Approach

This package should take approximately ten hours to work through however the sections have been designed in a way which enables users to dip in and out to suit their needs. At the start of each section a brief outline of what is covered will be outlined and linked to the above learning outcomes.

A key design of the package is to be interactive. While synthesis and summary of key information has been provided, the user will gain greater benefit by engaging with the directed reading, activities, short quizzes and case study that have been developed to support a deeper learning experience.

Also a range of material has been considered in the design of this package to try and suit most learning styles (VARK xxxx). If you find that a section does not suit then please review the additional resource section at the bottom for alternative options.

The following describes the main sections found below in this resource package.

Introduction
What is FES
When should I use FES
How do I use FES
General
Shoulder Subluxation
Motor control
Conclusion
Further Resources

Context - Why this Topic?
Stroke plays a large part and burden on society (Stroke Association 2015) and is currently the 4th largest cause of mortality in the UK (Stroke Association 2015). Although trends show decreased mortality rates over the last 20 years, it is still the leading cause of adult disability. The UK has approximately 1.2 million stroke survivors with half experiencing disability and 77% with upper limb difficulties (Stroke Association 2015).

In the UK the over 65s population is estimated to grow by 25% by 2020, which is a demographic where stroke incidence is higher. This could potentially lead to even greater numbers of survivors requiring support and rehabilitation from health care professions such as Physiotherapy.

Maintaining and improving people’s functional abilities is a key goal for physiotherapists working with those who have a stroke and FES is a technology that offers the potential to support this (ref xxxx). This goal aligns with current Scottish health and wellbeing policy aimed at driving improved health outcomes for patients (The Scottish Government 2015).

What is Functional Electrical Stimulation

Functional electrical stimulation (FES) is an assistive technology that works by stimulating peripheral nerves and muscles of a weakened part of the body. It activates contraction and relaxation of the muscles that have been affected by an upper motor neuron lesion. The muscles are triggered to contract during an activity, in order to improve function of completing these tasks. FES engages the patient and delivers feedback of a sensory and visual nature, which is said to be beneficial for stroke patients during their recovery and should promote motor re-learning (Dobkin and Dorsch 2013; Kawashima et al. 2013; Howlett et al. 2015; Odstock medical 2015).

Alongside stroke, conditions whereby FES may be effective include Cerebral Palsy, Parkinson’s Disease, Multiple Sclerosis and Spincal Cord Injuires if this is above T12, all of which being upper motor neuron injuries (Odstock medical 2006).

FES is not suitable for lower motor neuron lesions as lower motor neurons directly innervate skeletal muscles via the ventral horn of the spinal cord and are needed for voluntary muscle contraction. They contain both sensory and motor fibres (Odstock Medical 2006; Bear et al. 2007).

image  (Bear et al. 2007)

How it works/Physiology

Motor units are electrically stimulated by depolarization of motor axons, or terminal motor nerve braches. When depolarization reaches threshold an action potential occurs due to sodium flowing from extracellular to intracellular space, leading to the contraction of muscle (Neo stroke network 2015).

In FES it is the nerves that are stimulated rather than muscle, as they require a lesser current of that which would be needed to trigger muscles directly. Factors including distance from electrode to nerve fibre, size of motor unit, and surrounding tissue will all have an impact on the number and type of motor units activated.

If FES is effective muscle fibres will change in structure over the course of treatment with type II glycolytic fibres converting to type I oxidative skeletal muscle fibres due to improved resistance to fatigue (Gorman and Peckham 2014). Type II fibres create greater forces however fatigue more quickly, whereas type I fibres produce lesser force however take longer to fatigue (Sheffler and Chae 2007).

image 

If you require a refresher on the structure and function of motor neurons, visit this short youtube clip to familiarise yourself.  youtube video

For further revision of physiology please visit the book ‘Principles of Physiology’ by Levy, Koeppen and Stantion (2006).

Chapters of interest:

- chapter 3 – Generation and Conduction of Action Potential (Howard C. Kutchai)
- chapter 4 – Synaptic Transmission (Howard C. Kutchai)
- chapter 9 – Motor System (William D. Willis, Jr)

A limitation of FES is that muscles may fatigue (Thrasher et al. 2005). It is reported that the higher frequency that is selected, the quicker muscle fatigue will set in. Therefore to solve this issue a lower frequency should be selected. (reference)

There is argument for and against whether muscle strengthening can occur once fatigue has set in. It has been suggested that when fatigued, that no advantages can be gained from additional stimulation and therefore you should try to prevent fatigue. The opposite view however suggests that strengthening will only be achieved is the muscle fibre is worked to its maximum.

It appears that strengthening can occur if fatigue is within the muscle fibres due to cellular processes being activated, however is fatigue has resulted from neurotransmitter depletion or propogation failure, the muscle will not be strengthened as the fibre is not being stimulated (Robertson et al. 2006).
Response to continual stimulation may reduce due to the action potential decreasing the distance reached over membrane of the muscle fibre. (reference)

mindmap of types of stimualtion

FES System/Electrodes

FES systems include three mechanisms: the control, an electrical stimulator and electrodes which connects the FES with the nervous system (Gorman and Peckham 2014).

The electrical current activates the nerves via electrodes. These can be surface electrodes meaning they are placed on the skin which is the most common and detailed further below; percutaneous electrodes, which penetrate through the skin into the muscle or completely implanted electrodes, which receive stimulation from an external unit.

Surface electrodes

As well as stimulating muscle, surface electrodes may also be used to achieve a reflex action. Surface electrodes appear the most practical however there can be issue with disuse due to the sensory component, which may make stimulation of deeper muscles more difficult. Implanted and percutaneous electrodes can resolve some of these issues but the cost and practicality should be taken into consideration (Ewins and Durham 2005).

Parameters of FES needed when using surface electrodes can differ depending on factors such as material of the electrodes, placement and surface area. An issue with surface electrodes is that there can be difficulty contracting small individual muscles, and to activate deeper muscles, those more superficical must first be activated. Surface electrodes may also cause pain for some patients and it is reported that subcutaneous electrodes are more pleasant (Popaviz 2003).

Two electrodes should always be used however these can be unipolar or bipolar. Unipolar is the term for when one electrode is more active than another, due to their sizes. Biploar electrode placement means they are both the same size meaning the current at each site will be equal (Robertson 2006).

To further familiarise and gain greater understanding regarding use of electrdoes, please read pages 50-58 of Electrotherapy Explained – Princicples and Practice (Robertson et al. 2006).

table of parameters  (Allan and Goodman 2014) (SSAHPF 2014)

Specific parameters for the use of ES within shoulder subluxation and motor control will be detailed below in their specific sections.

Whats Avaialble?

Odstock medical is one of the main suppliers of FES devices, which vary in design and paramters available. The odstock 4 channel stimulator kit and microstim 2V2 kit are both simple to use in order to allow regular activity in the home environment. They have this in common however differ in output as the 4 channel stimulator can provide alternating or continuous output, unlike the microstim.
The odstock website has further images and descriptions of the FES kits available. Please visit the website to familiarise with the options available. The link is as follows: http://www.odstockmedical.com
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quiz 

How do I use Functional Electrical Stimulation

Recent Related Research (from <a href="http://www.ncbi.nlm.nih.gov/pubmed/">Pubmed</a>)

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References

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