Tonic Clonic Seizure Detected – OpenSeizureDetector

Benjamin had a tonic-clonic seizure this morning, so I thought it would be useful to describe how OpenSeizureDetector performed in detecting it.

Benjamin sat up and contorted in an unusual way – head looking up and to the left.
Sandie saw this on his video monitor and recognised it as a fit and set off up the stairs to check him.
When she found him, Benjamin was lying on his back with arms shaking, but not out stiff (his elbows were bent).
It was not one of his worst tonic-clonic seizures – he was not paralysed after it, just needed to sleep it off for a few hours.
OpenSeizureDetector alarmed as expected.

- Sandie spotted the seizure using the video monitor from Benjamin’s odd behaviour before OpenSeizureDetector did – this is because OpenSeizureDetector needs the shaking associated with a seizure to detect it, but Sandie spotted the odd movement before the shaking started.
- The first OpenSeizureDetector warning sounded about the time Sandie reached his bedroom.
- The warning re-set unepectedly. I think this was Benjamin falling bakwards, resulting in a lot of low frequency movement, which the detection algorithm assumes is not seizure-like movement..
- About 30 seconds later the warning re-initiated followed by full alarm.
- When the full alarm sounded, Benjamin was lying on his back with arms shaking, but not out stiff (elbows bent).
- Two full alarm initiations occurred before the seizure detector re-set as the movement subsided.
The spectra of the alarm and warning conditions are shown below.
The initial warning occurred at a peak frequency of 7 Hz. The full alarm occurred with peak movement at around 4-6 Hz.
These spectra are consistent with the type of movement OpenSeizureDetector is set up to detect – an excess of movement in the 3 to 8 Hz range compared to the rest of the spectrum.

It is encouraging that OpenSeizureDetector detected a tonic-clonic seizure as expected – the spectrum is consistent with the movement the system is designed to detect.
The re-set when Benjamin fell backwards is not what I had expected to happen. I think we need to add some hysteresis so we have to see a reset condition for a few analysis periods before resetting the alarm. This will increase the false alarm rate though…..