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Sensor bracelet detects epileptic seizures

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Introduction

With the help of the researchers at imec/Holst Centre, the Kempenhaeghe sleep and epilepsy clinic is developing a sensor bracelet for its epilepsy patients. The sensor bracelet is intended to alert family members and carers when the patient is suffering a seizure. The new development is necessary because the solutions commercially available today are simply not up to the task. Hans van Dijk and Joyce van Sluis from the Kempenhaeghe clinic tell us more about this development, which is designed to restore peace of mind to the lives of epilepsy patients and their families.

In the Netherlands, set amid the fields and farms of North Brabant, you will find Kempenhaeghe. Kempenhaeghe is a center of expertise for people suffering from epilepsy, sleep-related problems and neurological learning and developmental disorders. The complex also includes a residential center that is home to around 300 patients living with a complex form of epilepsy and mental retardation. The calm, relaxed atmosphere is something you feel immediately as you walk through the center.

But don’t be deceived, this peaceful setting cleverly masks all of the hard work that goes on behind the scenes, including in the ‘clinical physics’ department. This part of the center provides doctors with all of the very latest measuring equipment for research into the brain and sleep, guiding them in using the many devices and interpreting the results.

What is epilepsy?

Hans van Dijk, head of the clinical physics department, explains: “With epilepsy, patients find themselves battling with (unpredictable) periods of ‘short-circuits’ or hyperactivity in the brain. This can take a range of different forms. The best-known and most dangerous seizures are known as ‘tonic-clonic seizures’ in which patients make violent rhythmic movements with their arms and legs. Less well-known are ‘absence’ seizures, which occur mainly in children, causing them to appear as though they are daydreaming. Often, this form of epilepsy only comes to light when the child begins to fall behind at school as the result of being ‘absent’ too often during lessons. The causes of epilepsy can differ, too. One frequently occurring cause is a brain injury.”

There is a solution for some: medication and surgery

Fortunately, around 70% of epilepsy patients can be helped with medication. Hans van Dijk: “With some patients for whom medication is not sufficiently effective, an operation can offer a better outcome. To determine the source of the epilepsy, patients are admitted for a lengthy EEG examination, which is recorded on video. Using additional techniques, such as MRI, this makes it possible to accurately identify the area of the brain that needs to be removed. In some patients, brain probes are used to determine the exact location.”

The dangers of a seizure

If medication or surgery do not help, epilepsy patients are obliged to learn to live with their seizures. This is the case for many of the residents at the Kempenhaeghe residential care center. Hans van Dijk: “The most dangerous seizures are tonic-clonic ones. These begin with a phase in which the person tenses his or her muscles (the tonic phase), which is followed by violent movements of the arms and legs (clonic phase). It is important for someone to be with the patient when these seizures occur so that they don’t injure themselves. The patient also needs to be kept under observation for a short while after the seizure. This is due to the ‘sudden unexpected death by epilepsy’ syndrome (SUDEP) while can kill the patient. Clusters of seizures may also occur. These, of course, are also very dangerous.”

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Technology for detecting seizures

It is quite a challenge for everyone around the patient to be alert at all times when epileptic seizures are happening. You frequently hear stories about parents who sleep with their children in bed so that they can be alerted immediately when their child suffers a seizure. This is often an unsustainable situation. Hans van Dijk: “At the residential care center, we place sensor mats in our patients’ beds to notify the nurse when someone is having a seizure during the night. This, of course, only works for clonic seizures (with wild movements). Purely tonic seizures (with muscle tension) are not detected by the sensor mats. Yet these tonic seizures are still important, because they can also be dangerous. A tonic seizure is also often the first phase of a tonic-clonic seizure. If we were able to register the muscles tensing, we would also be able to detect a tonic-clonic seizure earlier in the process. Kempenhaeghe has been working for 15 years on developing a better solution for detecting seizures.”

One of the results of these years of work is the ‘NightWatch’. This is a sensor armband that patients wear round their upper arm to measure their heartbeat and movements. Livassured sells this product. Livassured is a spin-off from a consortium of epilepsy centers in the Netherlands of which Kempenhaeghe is also a part. Hans van Dijk: “We measure the heartbeat because studies show that the heart rate rises at the beginning of a seizure. So we measure movement to detect the clonic seizure. But we would like to go a step further and develop a sensor armband that also measures muscle tension in addition to heartbeat and movement. We hope that by recording these three factors, we will be able to detect a seizure with greater accuracy.”

Can accuracy be improved?

This is where imec/Holst Centre comes into the picture. They have produced a prototype of a sensor bracelet for Kempenhaeghe, which – just like the NightWatch – is worn on the upper arm. It combines ECG sensors (heartbeat), EMG sensors (muscle tension) and an accelerometer (movement). The armband has two electrodes with small wires that are attached in the region of the heart.

There are also two other electrodes with wires that attach to the shoulder muscles and a grounding electrode. Joyce van Sluis, a post-master’s student and qualified medical engineer, is doing her project at Kempenhaeghe and is responsible for setting up a trial with this sensor bracelet: “We have been given a 3-year grant to research whether we can detect seizures better based on heartbeat, muscle tension and movement. It is my job to record as many seizures as possible with the bracelet, with video and audio equipment acting as the gold standard. Based on these measurements and readings I will then develop an algorithm that enables a seizure to be recognized. Hopefully this will produce even better results than the NightWatch.”

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The sensor armband developed by imec/Holst Centre for Kempenhaeghe and which is currently being used in a trial for detecting seizures in epilepsy patients.

The future

Hans van Dijk: “If this additional parameter – muscle tension – turns out to be important, we will be able to market the new bracelet so that our residents and epilepsy patients can use the bracelet when they are at home. In the meantime, there are still a number of points to be ironed out: for example, the bracelet is not yet ideal to wear, mainly because of the electrodes and wires. This can be resolved by using a heart sensor that operates based on light (PPG); muscle tension can then be measured with dry electrodes in the bracelet. This is certainly technically feasible. By combining the expertise of imec/Holst Centre and Livassured, we will be able to bring this sort of product to market relatively quickly.”

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