07

Perspectives on:

I n s t i t u t e o f P h y s i c s a n d E n g i n e e r i n g i n M e d i c i n e

S p o t l i g h t o nElectronic Medical Implantsand Measuring Devices

physics and engineering in medicine and biologyInstitute of Physics

and Engineering in Medicine

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07Most of us take for granted the ability to move our limbs, and control our bladder movements, but for some people these tasks are impossible either as a result of disability - in some cases caused by a serious accident - or disease. To help combat these problems, scientists and engineers have developed electronic medical implants, often referred to as active medical implant devices, that can help some people by electrically stimulating nerves and muscles that are unable to work by themselves.

Meanwhile new electronic devices that can measure motion look set to aid people with mobility issues. A recently developed system that can analyse gait in less than ten minutes outside of laboratory conditions could prevent many potential falls and improve the mobility of patients with Parkinson’s disease, dementia, back problems and sports injuries by allowing prompt assessment and a corrective exercise regime to be implemented. In addition, a new activity monitoring system could speed up hospital discharges, and reduce the number of follow-up appointments needed for patients recovering from orthopaedic surgery - including hip and knee replacements.

Both these emerging types of technologies involve the transfer of signals or information from one place to another, which can occur via specialised wireless transmitters. Wireless technology is now becoming standard inside implanted cardiac pacemakers and defibrillators, enabling cardiac specialists to remotely monitor patients’ progress and so reduce the number of hospital appointments required. In addition, a wireless chip has been incorporated into a camera pill that can transmit images as it moves through the digestive system (see figure caption on back page), while similar wireless technology looks set to appear in a range of other implantable medical devices including neurostimulators and glucose monitors.

that are distributed, and technically supported, worldwide. Several hundred patients in the UK have Finetech’s Brindley Bladder Control System (see lower figure caption on right) fitted to improve urinary continence, bowel function, or penile erection, while other patients are benefiting from their STIMuSTEP® Dropped Foot Stimulator. The STIMuSTEP® is aimed specifically at stroke and Multiple Sclerosis (MS) patients with a condition known as dropped foot that causes a foot to point inwards and droop towards the ground. The STIMuSTEP® has a switch in the heel of the wearer’s shoe (see diagram on left) that triggers the turning on or off of the device controller. As soon as the heel is lifted, the signal from the controller triggers the implanted electrodes to stimulate the relevant leg muscles, which contract and so lift and level the front of the foot. The wearer can then take a step without their foot catching on the ground. As soon as the step is completed, and the foot is placed back on the ground, the device switches off. Studies have shown that patients with this device are able to walk twice as fast as without it. In addition, they do not have to raise their hips or swing their leg outward to take a step without falling over, so have a more natural gait.

Finetech Medical has also developed STIMuGRIP®, a system that enables an otherwise paralysed hand to grasp an object. This prototype product works in a similar way to the STIMuSTEP® device, with a controller that transmits signals through the skin to an implanted receiver, which converts the signals into a pulse sent to electrodes connected in this case directly to the paralysed muscles. Different actions can be carried out depending on the pre-programmed cycle of stimulation (resulting in muscular contraction) and relaxation selected by the user. The STIMuGRIP® was developed and underwent an initial clinical trial with three users as part of the recent €23 million four-year Healthy Aims project, funded under the European Union Information Society Technology Sixth Framework program. However, whilst these users reported benefits, a larger clinical trial will be needed before enough evidence of the benefits of the device are obtained to enable progression through the final regulatory procedures that must be passed before the device can be marketed.

Prototypes have been developed in conjunction with Zarlink Semiconductor’s Advanced Packaging Division based in Caldicot, Wales for wireless switching between the foot and controller for the STIMuSTEP® device. This would improve

Improving patient care with new electronic medical devices

The foot-switch operated controller for the STIMuSTEP® device (shown above top) is strapped to the patient’s leg directly above the circular implant receiver (on the right of the picture) which sits just beneath the skin. The wires coming from the implant receiver go to the electrodes, which as the diagram immediately above reveals are attached to the two main branches of the peroneal nerve which controls the outer side of the leg. Two weeks after the day surgery required to implant the device, the patient is assessed by a clinician who programs the rechargeable battery-powered controller to produce the appropriate stimulation for them to have as normal a gait as possible at a walking speed they find comfortable. Full time usage is gradually built up to over a training period of six to eighteen weeks.

Nerve and muscle stimulators

Electronic Medical Implants and Measuring Devices

Wireless communication

Picture courtesy of Finetech Medical Ltd.

Picture courtesy of Finetech Medical Ltd.

When nerves are damaged due to stroke, neurological conditions such as multiple sclerosis, or injury, the signals they normally send to muscles can be prevented from going through, which results in the muscle stopping working. However for certain groups of patients, movement can be restored to paralysed regions by stimulating the muscles or nerves artificially via a low-level pulse of electric current. This is known as Functional Electrical Stimulation (FES).

In the UK, Finetech Medical design and manufacture nerve and muscle stimulators

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the look of the system, and reduce the chance of damage by the cable - that currently carries the signal - catching on objects.

Meanwhile many cardiac patients fitted with a defibrillator in the UK now benefit from wireless technology. Defibrillators are implanted in the chest, and use electrical signals to correct dangerous abnormal heart rhythms. They also contain sensors that record physical functions such as heart rate and rhythm. In wireless defibrillators, encrypted data from these sensors is sent to a base station in the patient’s home, which forwards the data over the Internet to specialist cardiac physiologists who look for signs of dangerous heart rhythms. If detected, a cardiac consultant can then assess the data and change medication or defibrillator settings – potentially avoiding serious problems and hospitalisation. Previously, the only way to access this data was in hospital using a receiver held over the device, leading to delays in assessment and treatment. Currently wireless defibrillators made by Medtronic, St. Jude Medical (containing Zarlink technology), Boston Scientific, Sorin and BIOTRONIK are available for use in the UK.

The strap-on Pegasus-I gait analysis device developed - as part of the EU Healthy Aims project and subsequent Technology Strategy Board Gait Trainer Project - by UK-based European Technology for Business (ETB) Ltd (see right-hand image on front cover), can be used in almost any environment including a GP surgery. The device contains inertial measuring units which detect rotational and straight line movement about three axes at right angles to each other – that point up and down, left and right, and forwards and backwards respectively - and sends data collected from these units via a USB cable to a standard PC or laptop (see left image on front cover). Various parameters including joint angle, stride duration and variability, and phasing between the limbs can be determined by locating multiple Pegasus-I devices in suitable positions on legs, feet or the back, and using software also developed by ETB

This external rechargeable battery-powered controller for the Finetech-Brindley Bladder Control system sends signals via the illustrated lead and triangular transmitter block through the skin to an implanted receiver. The receiver converts these signals into electrical pulses that are sent to electrodes placed during the implant surgery on the nerves going to the bladder. These pulses cause the bladder and sphincter muscles to contract. While the bladder is contracted and the sphincter (which contracts to close the opening at the bottom of the bladder) is relaxed, the bladder will empty, eliminating the need for a catheter, and reducing the risk of associated infection. The system can be adjusted to suit each individual, and tends to work for around 30 years before requiring maintenance. In principle implants like the STIMuSTEP® (opposite) and STUMuGRIP® should last a lifetime. However if any of these devices malfunctions, or is damaged by an accident or fall, they can be replaced.

to analyse the data obtained. For example, to measure knee joint angle during movement one Pegasus-I would be strapped on above the knee and another strapped below the knee to record the orientation of calf and thigh, and so allow the joint angle to be calculated.

Estimates suggest that half a million of the UK’s elderly are at risk of falling, and as most falls are attributed to an abnormal gait, one goal for the ETB team is to provide a system that falls clinics could routinely use to quantify gait. This would enable exercises to be prescribed for people on the at risk register for falls, with the aim of improving their walking to the point where a fall is avoided. ETB in conjunction with the Bath Institute of Medical Engineering are currently conducting trials of the Pegasus-I device to discover which of the parameters it measures are most effective at revealing elderly people at risk of falling.

There is also potential for the Pegasus-I to help orthopaedic surgeons and physiotherapists monitor movement before and after treatments, and the London Knee Clinic is working with ETB to determine how the system can best be used to aid both diagnosis and rehabilitation for their patients. In addition, the devices could help athletes improve performance by analysing their leg movements during sports including cycling, golf and pole vaulting.

Meanwhile the Activ4Life ProV3.8® orthopaedic activity monitoring system recently developed and manufactured in the UK aims to reduce the amount of post-operative care, and provide early detection of complications, following orthopaedic surgery. The system consists of a monitor containing accelerometers that record movement in three directions, and a docking station. The monitor is recharged in the dock overnight (see uppermost picture above), while the recorded acceleration patterns are encrypted then sent via the mobile phone network to Activ4Life’s secure server. The patient can also report pain levels via buttons on the dock.

The small, lightweight Activ4Life ProV3.8® monitor attaches to the waist via medical grade sticky pads. It displays details of patients’ daily activity, along with exercise advice from their clinician. Both patients and clinicians can also access the data it records via Activ4Life’s secure website. Clinical trials have revealed a 10-12% improvement in clinical outcome for two hundred orthopaedic patients using this monitor for approximately 6 months after surgery. Activ4Life estimate this saved at least 20% of the normal cost of treating each patient, by reducing follow-up appointments, and encouraging patients to manage and maximise their recovery by avoiding either too much or too little activity. Around 80 monitors have so far been sold, primarily to clinicians interested in conducting research trials of the product.

Courtesy of Activ4Life Healthcare Technologies Ltd

Courtesy of Finetech Medical Ltd

Measuring devices

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Institute of Physics and Engineering in MedicineFairmount House230 Tadcaster RoadYork YO24 1ESUnited Kingdom

Enquiries:Tel: +44 (0)1904 610821Fax: +44 (0)1904 612279office@ipem.ac.ukwww.ipem.ac.uk

07Perspectives on:physics and engineering in medicine and biology

Perspectives is a series of publications which highlights new and emerging areas of research in physics and engineering, and discusses their application to the solution of problems in medicine and biology.

Acknowledgements

Much of the information in this perspective was kindly provided by Dr Diana Hodgins (European Technology for Business Ltd), Martin McHugh (Zarlink Semiconductor), Dr Ian Revie (Activ4Life), Dr Paul Roberts (Southampton University Hospital), and John Spensley (Finetech Medical Ltd). Thanks are also due to Sue Dunkerton (Health Tech and Medicines Knowledge Transfer Network) and Ed Goffin (Zarlink Semiconductor Inc.).Both cover images: Courtesy of European Technology for Business Ltd.

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I n s t i t u t e o f P h y s i c s a n d E n g i n e e r i n g i n M e d i c i n e

Different types of movement produce different acceleration patterns, and the system can so far differentiate between walking, running, shuffling, or taking the stairs. Newly collected data is compared with an activity profile from Activ4Life’s database of previous users that matches the operation, gender, age, BMI, and lifestyle of the current patient, so that either degeneration or improvement can be predicted. Exercise regimes are then prescribed to fit the evolving situation, thereby maximising recovery.

such as universities, hospitals and specialist manufacturers during product development. In addition, once new devices are commercially available they need to be widely marketed to clinicians and patients, emphasising the specific types of patients who would benefit.

September 2010

Future provision

In the same way that Wi-Fi technology only took off once all the different devices on the market could communicate with each other, experts say for home patient monitoring to become commonplace it is also imperative that future wireless medical devices from different manufacturers be able to work together as part of a network.

For nerve and muscle stimulators, experts warn that maximising use of these technologies will involve not only developing the devices, but also ensuring the correct types of patients receive them. It is also vital that they can - where appropriate - be successfully surgically implanted, and that both patients and medical staff are able to use them correctly. In addition, answering patient queries, gathering feedback from users and clinicians, and as a result continually improving user manuals will need to be an integral part of the service manufacturers provide, and should help with ongoing development of their products. Any small companies creating electronic measuring devices or medical implants are likely to require funding to pay for clinical trials that provide enough data for clinicians to be able to confidently prescribe a given product for a particular patient group. Liaison is also required between different organisations

This Given Imaging PillCam® can provide images of the small bowel as it moves through a patient after being swallowed. The wireless chip inside (shown here in front of the pill) was custom-designed by a Zarlink Semiconductor team, including UK-based hardware engineers. The camera capsule also includes a miniature camera, LED-based flash, and two silver-oxide batteries. The Zarlink chip transmits two images per second to an external data recorder, and provides physicians with over 50,000 pictures during its journey. More than 70 countries are now using this camera pill, and over a million have been swallowed, allowing diagnosis of a range of disorders including coeliac disease and tumours, and in some cases removing the need for exploratory surgery.

Zarlink Semiconductor and Given Imaging

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