SUDEP research

How we might prevent sudden unexpected death in epilepsy

Sudden unexpected death is a difficult – and sometimes a frightening or upsetting – subject to talk about, writes  Professor John Duncan. It is an important area of research at the NSE to try to find out why this happens and how it can be prevented.

Currently there are around 456,000 people in the UK with epilepsy, with 30,000 new cases a year. Every year around 600 of these people die suddenly due to their epilepsy.

One of the risk factors for sudden unexpected death in epilepsy (‘SUDEP’) is that it is usually unwitnessed and happens when people are alone, and more often at night during sleep than in the daytime.

Although we have known about SUDEP for many years we still do not know exactly why it happens. There are several possible causes: it could be that a person’s heart fails or their breathing is affected or something happens in the brain. Or it may be the result of these causes happening together.

The cardiac causes of SUDEP

A recorder implanted under the skin can be used to make continuous recordings of a person’s heart rate (a cardiogram). By studying the results of these recordings we have seen that an individual’s heart rate can slow during a seizure.

Cardiograms can also detect ‘long QT syndrome’, which is an abnormality of the way the electrical rhythms of the heart work. This can cause blackouts that can be misdiagnosed as epilepsy, but the way it is treated is quite different from epilepsy.

The respiratory causes of SUDEP

In general, if a person stops breathing there is a two-minute ‘window’ in which to get their breathing started again with basic cardiopulmonary resuscitation (cardiac massage) techniques. Apnoea (temporarily stopping breathing) and cyanosis (a blueish colour to the skin due to a lack of oxygen) can happen in complex partial and generalised  seizures. In some cases it may be possible to detect apnoea. While this can be monitored when someone is in  hospital it cannot be monitored effectively when they are at home.

At the NSE we are looking at possible ways of monitoring breathing to detect when apnoea happens, which is particularly important for people when they are at home. The devices that are currently available to detect seizures and breathing irregularities are not always appropriate: they are large, bulky, and require a lot of power. Also, the pressure pads that are used in these devices are not very sensitive – they may miss a seizure happening or give false alarms.

Developing an apnoea detection system

A couple of years ago we set ourselves the objective of developing a miniature, wearable device that can monitor breathing. Our criteria were that it had to non-intrusive (ie, not get in the way) usable in a variety of settings (for example, at home or in residential care and when travelling) and be suitable for longterm use.

It also had to be reliable, sensitive and specific (ie, giving few false-positives and no false-negatives) and able to raise the alarm and summon help. We therefore specified the design for a device which was:

• small, lightweight, hard-wearing yet comfortable
• attachable securely to the person’s skin or implantable under the skin
• low-powered, with a battery life of over 12 months
• able to send a radio signal to a base station (for example, in a pocket or on a nightstand) within a distance of two metres.

Crucially, it also had to contain a microchip to detect if a person’s breathing had stopped for 20 seconds and then send either an ‘all is well’ signal or an alarm signal to the base station. Our preferred option for monitoring the person’s breathing was to incorporate a tiny microphone to ‘listen’ to the sound of their windpipe. (In arriving at this solution we first rejected several other options, including using a probe in the person’s nose or an electromyogram to monitor electrical signals via a needle inserted in the chest wall, both of which would be very uncomfortable.)

A ‘mark 1’ version of the device has been constructed and tested on volunteers who pretend to have apnoea by holding their breath. So far it seems to work rather well.

Next steps

To be able to continue to develop versions 2, 3 and 4 of the device we need to get more funding (and it is hard to get funding for new things!) to make sure that the system works reliably. We also need to carry out more studies on volunteers – while they are sitting quietly, moving around, and with loud music playing – before trying it out on people with epilepsy (for example, while they are having video-EEG telemetry).

Then, over the next two to three years, we need to do longer-term studies to make sure the device works when users are moving around in everyday situations and not just when it is quiet and people are still.

In the future we hope to produce an implanted version to go under the skin, and an even smaller version specifically for children.

The components of the new device

The ‘mark’ 1 device contains:

• a tiny microphone (just 1mm wide) to listen to the user’s breathing
• a microchip (8mm wide) to detect and process the sound of breathing, and to filter out the general background noise in the environment
• a radio transmitter to send the signals to the base station
• a hearing aid battery to provide power.

Did you find this article interesting?

To read more articles like this, join one of our membership schemes.