eeg-132 pract
TRANSCRIPT
ELECTROENCEPHALOGRAPHY(EEG)
Dr. Shaikh Mujeeb AhmedM.B.B.S. MD. (PHYSIOLOGY)
EEG
The electroencephalogram (EEG) is a recording of the electrical activity of the brain from the scalp.
The first recordings were made by Hans Berger in 1929
Origin of EEG waves
Electroencephalogram
EEG is the record of electrical activity of brain( superficial layer i.e. the dendrites of pyramidal cells) by placing the electrodes on the scalp.
Generation of large EEG signals by synchronous activity
Objectives of EEG practical
Familiarize with the principles of techniques involved
Count frequencies and measure the amplitudes of the record obtained.
Categories the records into appropriate rhythms – α, β, θ,and δ.
Cont…
Objectives of EEG practical
Identify and describe changes produced by provocation tests.
e.g. eye opening & closing, intermittent photic stimulation (IPS) clapping sound, induce thinking & hyperventilation.
Appreciate clinical uses of EEG
EEG Waves
Alpha wave -- 8 – 13 Hz. Beta wave -- >13 Hz. (14 – 30 Hz.) Theta wave -- 4 – 7.5 Hz. Delta waves – 1 – 3.5 Hz.
D T A B
Different types of brain waves in normal EEG
EEG Recording From Normal Adult Male
Alpha wave
rhythmic, 8-13 Hz mostly on occipital lobe 20-200 μ V normal, relaxed awake rhythm with eyes
closed
Beta wave
irregular, 14-30 Hz mostly on temporal and frontal lobe mental activity excitement
Theta wave
rhythmic, 4-7 Hz Drowsy, sleep
Delta wave
slow, < 3.5 Hz in adults normal sleep rhythm
Different types of brain waves in normal EEG
Rhythm Frequency(Hz)
Amplitude(uV)
Recording& Location
Alpha(α) 8 – 13 50 – 100 Adults, rest, eyes closed.Occipital region
Beta(β) 14 - 30 20 Adult, mental activityFrontal region
Theta(θ) 5 – 7 Above 50 Children, drowsy adult, emotional distressOccipital
Delta(δ) 2 – 4 Above 50 Children in sleep
D T A B
Requirements
EEG machine (8/16 channels). Silver cup electrodes/metallic bridge
electrodes. Electrode jelly. Rubber cap. Quiet dark comfortable room. Skin pencil & measuring tape.
Computerized EEG Machine
Electrode Positioning system
EEG Electrodes
Sliver Electrodes Electrodes Cap
Procedure of EEG recording
A standard EEG makes use of 21 electrodes linked in various ways (Montage).
Ask the subject to lie down in bed. Apply electrode according to 10/20%
system. Check the impedance of the
electrodes.
10 /20 % system of EEG electrode placement
Procedure of EEG recording
Ask the subject to close his/her eyes. Select a montage. Press run switches on to run the
paper.
Procedure of EEG recording
Press the calibration knob to check voltages & time constant.
Always observe subject for any abnormal muscle activity.
Ask the subject to open eyes for 10 sec.and ask him/her to close eyes. (do this procedure for several times in each montage)
EEG Electrodes Each electrode site is labeled with a letter
and a number. The letter refers to the area of brain
underlying the electrode e.g. F - Frontal lobe and T - Temporal lobe. Even numbers denote the right side of the
head and Odd numbers the left side of the head.
Two types of recording
Bipolar – both the electrodes are at active site Bipolar montage are parasagital montage.
Unipolar – one electrode is active and the other is indifferent kept at ear lobe.
Always watch for any abnormal muscle activity.
Ask the subject to open eyes for 10 sec. then ask them to close the eyes.
Montage
Different sets of electrode arrangement on the scalp by 10 – 20 system is known as montage.
21 electrodes are attached to give 8 or 16 channels recording.
Analysis
Electrical activity from the brain consist of primarily of rhythms.
They are named according to their frequencies (Hz) and amplitude in micro volt (μv).
Different rhythms at different ages and different conditions (level of consciousness)
Usually one dominant frequency (background rhythm)
Factor influencing EEG Age
Infancy – theta, delta wave Child – alpha formation. Adult – all four waves.
Level of consciousness (sleep) Hypocapnia(hyperventilation) slow & high
amplitude waves. Hypoglycemia Hypothermia Low glucocorticoids Slow waves
NORMAL EEG CHANGES
Desynchronization or Alpha block
Cause: Eyes opening (after closure) Thinking by the subject (mathematical calculation)
Sound (clapping)
Eye opening
Alpha rhythm changes to beta on eye opening (desynchronization / α- block)
Thinking
Beta waves are observed
Provocation test
Intermittent photic stimulation Increase rate & decrease amplitude
Hyperventilation Decrease rate & increase in
amplitude
Use of EEG Epilepsy
Generalized (grandmal) seizures. Absence (petitmal) seizures.
Localize brain tumors. Sleep disorders (Polysomnography)
Narcolepsy Sleep apnea syndrome Insomnia and parasomnia
Helpful in knowing the cortical activity, toxicity, hypoxia and encephalopathy &
Determination of brain death. Flat EEG(absence of electrical activity) on two records run
24 hrs apart.
Sleep studies The EEG is frequently used in the
investigation of sleep disorders especially sleep apnoea.
Polysomnography : EEG activity together with
heart rate, airflow, respiration, oxygen saturation and limb movement
Sleep patterns of EEG There are two different kinds of sleep:
Rapid eye movement sleep (REM-Sleep) Non-REM sleep (NREM sleep)/ slow wave
sleep NREM sleep is again divided into 4
stages (I to IV). The EEG pattern in sleep is given in the following table:
Stages of sleep EEG pattern Somatic or Behavioral changes
Alert Alpha activity on eye closedDesynchronization on eye opening
Respond to verbal commands
I (Drowsiness) Alpha dropout & appearance of vertex waves & theta.
Reduced HR & RR
II (Light sleep) Sleep spindles, vertex sharp waves & K-complexes
Reduced HR & RR
III ( Deep Sleep) Much slow background K-complexes
Reduced HR & RR
IV (very deep sleep)
Synchronous delta waves, some K-complexes
Reduced HR & RR
REM sleep(paradoxical sleep)
Desynchronization with faster frequencies
HR, BP & RR irregularMarked hypotoniaRapid eye movement 50 – 60 /min.Dreaming threshold of arousal
Changes in brain waves during different stages of sleep &
wakefulness
Changes in brain waves during different stages of sleep &
wakefulness
Sleep Spindle
K - complex
EEG & Epilepsy
EEG in different types of epilepsy
Gra
nd
mal s
eizu
re
Petitm
al s
eiz
ure
Video monitoring
Simultaneous video monitoring of the patient during the EEG recording is becoming more popular. It allows the physician to closely correlate EEG waveforms with the patients activity and may help produce a more accurate diagnosis.
EEG Artifacts Biological artifacts
Eye artifacts (including eyeball, ocular muscles and eyelid)
ECG artifacts EMG artifacts Glossokinetic artifacts (minor tongue
movements)
External artifacts Movement by the patient settling of the electrodes Poor grounding of the EEG electrodes the presence of an IV drip
ECG Artifacts
LET’S ANSWER
What is EEG and what is montage?
The electroencephalogram (EEG) is a recording of the electrical activity of the brain from the scalp.
Arrangements of electrodes by 10/20% system is known as montage.
What is the advantage of provocation test while recording EEG?
Provocation test e.g. hyperventilation, intermittent photic stimulation are done to trigger the epileptic focus.
Compare & contrast Alpha & Beta waves of EEG
Alpha In awake resting
with eyes closed Frequency 8 – 13 Hz.
Voltage – 50uV.
Beta In awake thinking
subjects. Frequency - >13Hz.
(14 – 30 Hz.) Voltage – 20uV.
What stage of sleep is indicated by slow waves of EEG(4 – 7Hz.) ?
4 – 7 Hz. (Theta) waves are seen during stage 2 & 3 (light and deep ) sleep
In the following tracing of EEG what changes do you observe after point “A”.What may be it’s possible cause?
Rhythm has changed from α toβ(at point “A”) ,it is called alpha block or desynchronization.
Causes: Eyes opening Thinking e.g. mathematical calculations. Sound (clapping)
What changes are seen in EEG of an epileptic child suffering from absence seizure (petit mal)?
In petit mal spike and wave (dome shaped) 3 cps. Pattern is seen.