Implantable micro-sensors and micro-systems for ambulatory

measurement and control in medical products.

Proposal Acronym: Healthy AIMS

(Ambient Intelligent Micro-Systems for Health)

European Union 6th Framework Programme Integrated Project

Contract No. 001837

 

Healthy AIMS WP10

FES

The problem

Loss of upper or lower limb mobility due to paralysis is a problem effecting many hundreds of thousands of individuals in Europe each year. About 600,000 are paralysed due to stroke, about 20,000 due to cerebral palsy, a similar number due to multiple sclerosis and around 6000 due to spinal cord injury. As medical care improves the life expectancy has increased leading to many more people with paralysis living in the community. Despite greet advance in medical science, little has been possible to restore useful function to affected limbs.

FES (Functional Electrical Stimulation) is a technique that produces useful controllable movement in paralysed muscles by the application of electrical impulses to the nerves that supply the effected muscle. Traditionally, stimulation has been applied by the use of skin surface electrodes. While this has been relatively successfully used for exercise applications and the correction of dropped foot (the inability to lift the foot as it is brought forward in gait) the further applications have been limited by practicality of applying the necessary hardware each time the system is used. These problems would be removed by the use of an implanted FES device, significantly extending the usefulness of the systems. Several attempts have been made to develop such technology and useful benefits have been demonstrated in particular the provision of a useful grasp to tetraplegic and the correction of dropped foot in stroke. However, to date, systems have been application pacific and relatively expensive. Additionally, devices have been "open loop", lacking feedback of the user's situation, which could be used to improve the performance, the systems.

The nature of the disability varies between the patient groups. The paralysis in the case of stroke and cerebral palsy is incomplete and spasticity is a common problem, usually in the flexor muscle groups in the upper limb and extensors of the lower limbs. In the upper limb often, as the severity of a case increases, the problem progresses to proximal areas of the limb. In less severe cases the hand may only be significantly effected while the elbow and shoulder are added to the problem as the severity of the case increases. In spinal cord injury, the paten of paralysis can vary from incomplete injuries where anywhere from a few to most muscles being effected below the spinal cord lesion to a complete lesion where all the muscles will be effected. It is therefore plain that a range of solutions is required to restore function in all these different cases. However, each solution requires common components:

By developing a modular design of implant, technology can be efficiently shared between applications, lowering overall costs and providing a common philosophy to solutions for different clinical problems. The commonality will allow greater and more rapid dissemination of the technology to clinical users throughout the EU.

The implanted device and external control hardware will be developed by partners in the Healthy AIMS project, lead by Finetech Medical ltd. Salisbury's role is to identify clinical applications for the device, investigate the feasibly of these interventions and plan the clinical procedures for the implementation. The control techniques required for the recipient to use the device will be developed and finally a number of procedures will be carried out with volunteers to demonstrate the use of the technology. Information from the clinical investigation will be used to plan larger clinical trials to be carried out at a later stage (not under present funding)

 

Possible applications

In this project we wish to develop areas of use of the implant system, building directly on clinical and R&D experience in Salisbury District Hospital. We plan to look at three principal areas, upper limb function, gait assistance and standing / transfer function. The first two areas are applicable to stroke, incomplete spinal cord injury and cerebral palsy, the last area is specific to paraplegia.

Improvement of hand function following hemiplegia or spinal cord injury

The range of functional loss following neurological insult can be considerable. In the simplest application stimulation of the post interosseus nerve could be used to open the hand, allowing people whom have had a stroke to grasp objects using volitional control. Residual EMG (electromyogram- the electrical signals detectable in a contracting muscle) from partially paralysed muscles could be used to control the system, a technique already demonstrated in Salisbury using skin surface FES techniques. In more complex cases, additional stimulation channels would be required to control the position of the thumb and wrist and possibly provide active closing of the hand, certainly a requirement for tetraplegia. It is also likely that elbow and shoulder control could be improved by activation of the triceps, deltoid and other muscles. Where residual EMG is not available, implanted movement sensors could be used to detect the intention to produce a movement by detecting small initial movements or by movement of other parts of the body, such as the shoulder. Surgical techniques will be developed based on the team's extensive experience of the NeuroControl Freehand system and tendon transfer techniques.

Gait assistance following hemiplegia or incomplete spinal cord injury

Dropped foot is a common problem following hemiplegia and incomplete SCI and FES is routinely used to alleviate this problem. However, often problems still remain with controlling other aspects of gait, in particular, knee and hip control. We have already developed a range of procedures using external FES in Salisbury for use with a 2 channel stimulator. These will be adapted and expanded to exploit the capabilities of the implant. For example, hamstrings can be added to improve knee flexion in the swing phase. In the stance phase, the calf muscle group can be added to improve ankle and knee stability and also provide push off at terminal stance. Also in the stance phase, the gluteal muscles can be used to provide hip extension and abduction and quadriceps can be added to provide weight bearing. Present protocols for control use foot switches to initiate the stimulation sequences. Collaboration with Healthy AIMS partners at the University of Salford will develop the use of inertial sensors for control, allowing a totally implanted system.

Standing and transfer assistance in complete paraplegics.

It is relatively straightforward to produce standing by stimulation of the quadriceps muscles. However, the muscle fatigue within a few minutes requiring the stimulation level to be adjusted. A surface FES system has been developed in Salisbury that uses knee angle as a feed back parameter to determine stimulation level. As the quadriceps fatigue, the knee will flex. This is detected and a PID algorithm used to bring the knee back into extension. This significantly improves the safety of standing, preventing fatigue or involuntary muscle spasm from coursing the user to fall. Over stimulation of muscles is also prevented, leading to prolonged function. In an implanted version of the system would remove the need for extensive external hardware, which reduces the appeal of the existing device. It would also allow further functionality to be added for individuals who have problems extending their hips or controlling the posture of the back. Sensors will be used to detect hip and back position and gluteal and lumbar muscles used to control posture and improve the user's balance. Existing control techniques will be adapted to use the new sensors and greater range of muscles.

For more information about the other parts of the Healthy AIMS projects click Healthy AIMS.


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