Clinicians guide to EEG-electroencephalogram Flashcards
History of EEG
The first human EEG recording was obtained by Hans Berger in 1924. The upper signal is EEG and the lower is a 10Hz timing signal.
Hans Berger, the first person to record EEG brainwaves in humans
WHere to place electrodes in EEG
Standardised so results across different trust can compare
One important tone - CZ (intersection point between the coronal plane and sagittal plane). All other electrodes placed in relation to this
EEG process
- Physiologists conduct the process and the medically trained neurophysiologists interpret the results.
- Noninvasive, pain-free. 20-30mins in total
Layers cortex - neuropathologically defined (neuroexcitatory and inhibitor neurons working together).
Where electrical activity comes from in EEG - Electrical activity from summated electrical activity from cortex.
Differential Amplifiers
- Magnifies the voltage input - so you can read output easier
- Subtracts the common components in signals between 2 inputs and amplifies this
- Useful in biological systems - can detect small differences between 2 inputs
Montage
- Reflects way electrodes are all connected and referenced to each other and then displayed on screen
- Eg - there are 2 common ways - longitudinal bipolar montage and horizontal bipolar montage. We are taking electrodes in standardized electrodes and sign them as input 1 and 2 to get different EEG channels.
- F3 input 1, compare to C3 and have second EEG channel F3C3. DO same on right side brain etc
Longitudinal Bipolar montage on EEG
Multiple channels reflecting difference between electrodes
Green - second markers
Red markers - added by technician added.
Downside - reference in montage. Compare leads and then down lateral and downsides and up the middle.
Difference in ptoential between 2 points
Transvere bipolar montage
Input lead I negative in respect to Lead 2 then up deflection
Downward reflection then lead i positive in relation to lead 2
EEG Interpretation
- Age of patient
- CLinical state of patient - awake, drowsy, asleep
- Montage
- Wave forms - how many squiggles in each 1 second (frequency)
SO we know background normal rhythm
Alpha - normal in adults resting partiuclarly over occipital region
Beta rhythms - fast with lower amplitude - normal in adults if ocncentrating
Theta and delta can be normal in children and sleep but not if patient awake etc.
Waves in EEG
Rhythm
Alpha rhythm
WHat rhythm eeg
1-2 waveforms, high amplitude, slow activity widespread across EEG
Generlaised delta acitvity and worrying in right circumstances
- 20 Male
- Collapsed without warning
- Witnessed to become stiff, and then started jerking. Foaming at mouth, and became cyanosed. Breathing pattern changed. Incontinent of urine.
- Lasted 2 minutes
- Recovered slowly over 30 minutes, and was confused afterwards.
- Headache, tongue biting.
- Typical history of seizure - commonly presenting complaint
- WHen presents like this - invetsigate why happened and risk of it happening again.
- WHy - exclude tumours, previous strokes (so do MRI),r equest EEG (check risk seizure occurring again rather than diagnose here)
- First fits common
Prediction risk seizure recurrence after single seizure and early epilepsy
- Single seizure - prognostic index 0
- identified if had 2+ seizure sbefor epresentation then prognostic index 1/2
- Neurologicla disorder - 1
- Abnormal EEG - 1
- Combine to risk classification group.
- Low risk - only one seizure and normla mRI and EEG (0 score). 1 in 5 had further seizure, 1 in 4 by 3 years and 1 in 3 by 5years without treatment. No anticvoulsant with normal EEG here
Study 1500 patioents