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Medicine and Health

Restoring mobility to paralytics

   
 
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The technologies available are likely to be of benefit to the partially disabled. Implantable technology should make it possible to help a much larger number of patients suffering from various forms of paralysis.
In many cases, damage to the spinal cord and strokes result in various types of paralysis. Nowadays, thanks to neural prostheses, electrical stimulation makes it possible to restore certain functions - such as the activity of the bladder and respiratory organs. Researchers in the Neuros network are studying the application of this technique to the particularly complex field of mobility. This European scientific collaboration has already resulted in the development of a system likely to be of help to the partially disabled. It also opens up very interesting prospects for the creation of autonomous light-weight implant devices capable of restoring movement to patients suffering from many types of paralysis.

 

There are several thousand cases of damaged spinal cords each year, the majority of them affecting young people (60 % between the ages of 18 and 30). Such damage often results in paralysis, since the neuromuscular system - although intact - no longer receives commands from the central nervous system. In addition to the personal tragedies caused by such damage, important social costs are incurred through the need to provide life-long care for the patients. The restoration of some degree of mobility would considerably improve the quality of life of disabled persons by offering them access to numerous occupations - mainly in the professional sector. Furthermore, the restoration of partial mobility is also essential in order to avoid certain secondary effects such as demineralisation of the bones, kidney or bladder stones, infections, contractures, etc.

"A neural prosthesis delivers electric impulses which produce an action potential in the nerves linked to the paralysed muscles," explains Iddo Bante, the coordinator of the Neuros project. While the principle is simple, its translation into clinical practice encounters control system difficulties. Sensors are needed to deliver the desired stimulation to the paralysed limbs; information on the movement performed needs to be fed back to the system; care also has to be taken to avoid muscular fatigue entailed by this non-physiological electrical activity. Furthermore, existing systems demand particularly high levels of user attention.

The Neuros network aims to develop methods and techniques designed to make the neural prosthesis concept fully applicable to mobility. This objective calls for a triple approach: the development of autonomous control systems, the use of information obtained from natural sensors, and the development of stimulation systems and electrodes that permit highly selective muscular activation.

"The implementation of such a project requires research of a very high standard, which brings us to another fundamental objective of the Neuros network, namely to ensure the ongoing training of young scientists. Since the mid-1980s, our network has attained the critical mass necessary to conduct work of this quality. European researchers working in this field have established some very useful contacts, and their collaboration has been given a powerful boost through the training and mobility programme."

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From the intention to the reaction
The first difficulty encountered in creating a neural prosthesis is how to identify the user's intention. "We are not seeking to use direct signals from the central nervous system, since these do not allow sufficiently clear interpretation for the control of a neural prosthesis. Accordingly, we translate the person's intention by measuring movements, forces or even neural electrical activity in those parts of the body over which the patient is still capable of exercising voluntary control."

Researchers at the University of Ålborg (Denmark) recently succeeded in demonstrating the possibility of selectively recording signals emitted by sensory nerves, going on to show that these signals are perfectly usable for the creation of an autonomous functional electrical stimulation (FES) system. Amplifiers for these nerve signals have been developed by a London-based team along with permanently implantable electrodes to record nerve signals and to stimulate the neuromuscular system.

However, a neural prosthesis can only be truly autonomous provided that it receives feedback on the movement performed. This is why the Danish researchers are concentrating on picking up signals on the skin to feed to the control loops of the neural prostheses. "The dynamic relationship between the signal measured by the electrodes and the pressure applied on the skin has been determined. On this basis, the signals have been used in two applications. The first sought to determine foot contact in a walking-aid system and the second to detect slippage in an FES-controlled prehensile hand system."

In order to ensure autonomous mobility, the neural prosthesis also needs to be informed of the position of the body and the limbs, without having to depend on external equipment. "At the University of Twente we have developed a triaxial accelerometer - capable of assessing acceleration in three dimensions - which measures the movements and orientation of certain parts of the body. This instrument does not need to be connected to any laboratory equipment or external reference, as is the case with other systems. Furthermore, its energy consumption is low, and its very small size (3 cubic millimetres) allows it to be implanted."

Effective strategies
The control strategies developed by the European researchers have been successfully tested. "The methods which permit the interpretation of the user's intentions, in terms of the motor skill to be exercised, have proved perfectly effective and do not require the user to give explicit commands for each movement which he or she wishes to perform. Control strategies for certain actions - getting up, remaining in an upright position - have also been developed and simulated on biomechanical models. Trials are currently under way. As a next step, the most promising of these strategies will be transferred to clinical systems. Although not directly linked to the objectives of Neuros, this supplementary stage reflects the aims of many other European projects, notably Tide Crest, in which we are also actively involved."

"We hope that European industry will become increasingly involved," Iddo Bante stresses. "The technologies already available are likely to benefit the partially disabled who have difficulty in walking. As for the implantable easy-to-use autonomous technology which is now within our reach, this should enable us to provide effective neural prostheses of benefit to a much larger number of patients suffering from various forms of paralysis."

 

 

Project Title:  
Neuromuscular sensing and stimulation (Neuros)

Programmes:
Training and mobility of researchers

Contract Reference: FMRX960021

CORDIS databaseFor more information on this project,
go to the Cordis database Record

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