Introduction

The signal generated by different portions of the biological organs is

commonly termed as biosignal. Every organ, tissue and cell of living
body produces its own monitoring signal to indicate its activity. The
signal is classified broadly into two categories:

Electrical:
Produced in the different organs of body even in the
cellular level due to the change in the ionic gradient
Directly measured by electrodes

Non-electrical:
Acquisitioned and Converted by transducers
 Topic Contents
ECG
EEG
EMG
ENG
ERG
EOG
Anatomy of the Heart
ECG: Electrical conduction in heart
Cardiac Conduction
Ion Flow in Cardiac Cells
Action Potential of Cardiac Muscle
Sequence of Activity
12-Lead ECG
 ECG Parameters

Waves
P wave: depolarization of the atrial muscle
QRS complex: repolarization of the atria &depolarization of the ventricles
T wave: ventricular repolarization
U wave: if present, after-potential in the ventricular muscle
Intervals
P-Q: delay of excitation in the fibers near the AV node
P-R: start of the P wave to the start of the QRS complex
(time for depolarization to pass from the SA node via the
atria, AV node and His-Purkinje system to the ventricles)
Q-T: start of the QRS complex to the end of the T wave
(time taken to depolarize and repolarize the ventricles)
S-T: end of QRS complex to start of the T wave
(all cells are normally depolarized during this phase)
 ECG Parameters

Normal values of ECG:

Heart rate 120 bpm
Amplitudes:
P wave 0.25 mV
R wave 1.60 mV
Q wave 25% of R wave
T wave 0.1 to 0.5 mV
Durations:
P-R interval 0.12 to 0.20 sec
Q-T interval 0.35 to 0.44 sec
S-T interval 0.05 to 0.15 sec
P wave interval 0.11 sec
QRS interval 0.09 sec
ECG and Blood Pumping
 Cardiac Cycle

Two Phases:
Systole: Ventricular
Contraction
Diastole: Ventricular
relaxation

Activities:
Blood pressure
Blood volume
Heart sounds
Cardiac Cycle
 Electrocardiogram

Cardiac Electrical Activity

Depolarization and repolarization of cardiac muscles
Consists of waves, intervals and segments
 ECG Genesis

Excursion of trans-membrane potential that occurs in the

atria and ventricles when they become active and recover

Every portion has different shape of bioelectric potential

SA node: half-circle shape
Atrium: Quick rise and fall
Ventricle: quick rise but slow fall
Three theories:
Membrane theory
Interference theory
Dipole theory
 Membrane Theory
Refractory period is long
Heart is small compared to the cardiovascular system
Can explain the direction of action and recovery

Active cells are electro-negative viewing from outside

If excitation and recovery in the same direction, we have
alternate potential curve
Curve of same polarity is obtained when recovery is in
opposite of excitation
Knowing the polarity, direction can be understood
Limitations:
0 potential for
electrodes placed perpendicular to excitation
if excitation starts midway between electrodes
Placement of electrodes is very important!!!
 Interference Theory
Better bridge between ECG and trans-membrane potential
Can explain the shape of ECG

Potential seen by two recording electrodes is the instantaneous

algebraic sum of the potential under each electrode (monophasic
action potential, MAP)

V = V1+V2(inverted and delayed)

Consider Ventricular potential

The shape is similar to QRS and T waves

T is inverted due to rich coronary circulation
 Dipole Theory

Viewed from surface active cells are electronegative wrt resting

or recovered cells
Possible to express boundary between two regions as an array of
dipoles
Extensively used to explain ECG patterns obtained from body
surface leads
 ECG Lead
10 electrodes: 4 in limbs, 6 in chest
ECG collected as potential difference between combination of electrodes
Lead: signal between any two electrode or combination
6 limb leads and 6 chest leads

Limb leads: only limb electrodes are used, 2 types

Bipolar limb leads: potential in 2 limbs, third limb is kept
connected with ground (I, II, III)
Unipolar limb leads: also known as augmented leads, one limb
to +ve and rest 2 are jointly in ve (aVL, aVR, aVF)
Chest Leads: one chest electrode to +ve, 3 limb electrodes are jointly to ve. Also
known as V-leads (V1, V2, V3, V4, V5, V6)

Why so many leads?

Information available in one lead is not available in others
Total information is obtained by combined information of all leads
 Lead Diagrams: Bipolar limb leads

Lead I: RA to LA
Lead II: RA to LL
Lead III: LA to LL
RL is always grounded
 Lead Diagrams: Unipolar limb leads

aVR: RA to +ve LA & LL to -ve

aVL: LA to +ve RA & LL to -ve
aVF: LL to +ve RA & LA to -ve

RL is always grounded
Lead Diagrams: V leads
 Normal ECG
P wave
inverted in aVR
most prominent in I & II and almost equal
less in III, aVL and aVF
QRS complex
large and inverted in aVR
largest in II
less and equal in I and aVF
least in III and aVL
T wave
almost 0 in III
almost equal in I and II

V leads
excitation starts at V3 and moves both ways
Normal ECG
 Changes in ECG
Amplitude and duration of wave and/or complex
Interval and/or segment length
Phase reversal
Absence and/or multitude of some waves
Base line
Heart rate: too high (Tachycardia) or too low (Bradycardia)

Why?
change in ion due to
changed concentration in normal fluid flow
changed fluid with normal concentration
obstruction in pathways
 Cardiac Abnormality

Not all are detectable by ECG

Only five are discussed: detectable in ECG

Atrio-ventricular (AV) Block

Atrial Arrhythmias
Ventricular Recovery and Injury
Ventricular Fibrillation (VF)
Bundle Branch Block (BBB)
 AV Block
Disturbance in the
conduction of excitation
from atria to ventricles
Normal TPR= 0.2 sec
1st degree (1D) block
TPR> 0.2 sec and ECG
organized
2nd degree (2D) block
multiple of P wave for
each QRS (2:1, 3:1, etc
2D)
3D or Total Block
atrial pulse does not
propagate to ventricles
AV node starts giving
pulse (QRS)
No fixed relation
between P and QRS
 Atrial Arrhythmia
Change in metabolism in atria
faster ion movement
high rhythmicity of atria (atrial tachycardia)

HR > 200 bpm but organized, atrial flutter

Recovery of atria seen in ECG
 Ventricular Recovery and Injury
Ventricular recovery: T-wave and S-T segment

Less oxygenated blood in ventricles

full repolarization may not occur
S-T segment shifts upwards
Coronary artery becomes blocked
myocardial cells cannot sustain normal metabolism andtheir cell membranes
depolarize and remain in this state as the cells die and are replaced by scar
tissue (Myocardial Infarction, MI)
Net result
Early shift in the S-T segment
A change in the magnitude of the Q wave.
Problems
Breathing difficulty (Paraxysmal Disposal)
Lung diseases
Ventricular Recovery and Injury
 Ventricular Fibrillation
Loss in synchronism of action between atria and ventricles
Normal rhythm is replaced by rapid irregular twitching of muscular wall
Loss of pumping in the ventricles
Fall in blood pressure to a near-zero level
Cardiac output is zero
Activity of ventricle is reduced
Magnitude of QRS decreases
Conduction of A-V node, His bundle and Purkinje Fibers absent
QRS-T waves replaced by fibrillation waves
Patients may die within some minutes
Not self-correcting
 Ventricular Fibrillation
Remedy
Cardiopulmonary resuscitation (CPR)
chest is rhythmically and forcefully compressed to squeeze blood
out of the heart
lungs are inflated rhythmically by mouth-to-mouth breathing
Ventricular defibrillation (VD)
passing a pulse of current through the heart
failure of VD means end of life
 Bundle Branch Block
Failure of His bundle (main or branch) to transmit excitation
Ventricular Conduction: AV node, His bundle (with left and right branches) and
Purkinje fibers where propagation velocity is higher than in ventricular muscle
both ventricular contract simultaneously with maximum force
Block of excitation in any branch
Late excitation (depolarization)
Prolonged QRS
Excitation first appears on the surface of
right ventricles due to
The nature of the conduction system
Differing thicknesses of the
ventricular myocardium

Normal activation of ventricle produces

R-S wave in V1 , duration 0.02 sec
Q-R wave in V6 , duration 0.04 sec
R is prominent in V6
 Left Bundle Branch Block
Failure of left bundle to transmit excitation

Right-sided V leads show a large, broad, downward wave

Left-sided V leads show a large, broad, upward wave
V5-V6: QRS is prolonged downward
V1-3: little evidence of delayed conduction
 Right Bundle Branch Block
Failure of right bundle to transmit excitation

Left-sided V leads show a large, broad, downward wave

Left-sided V leads show a prominent S wave
V1-3: QRS is prolonged and M-shaped
Bundle Branch Block
 Electroencephalogram (EEG)
Electroencephalogram (EEG) refers to the recording of the brain's spontaneous
electrical activity over a period of time, as recorded from multiple electrodes
placed on the scalp.
Diagnostic applications generally focus on the spectral content of EEG, that is,
the type of neural oscillations that can be observed in EEG signals.
EEG measures voltage fluctuations resulting from ionic current within the
neurons of the brain.
EEG is most often used to diagnose epilepsy, which causes abnormalities in EEG
readings.
EEG is also used to diagnose sleep disorders, coma, encephalopathies, and
brain death.
EEG used to be a first-line method of diagnosis for tumors, stroke and other
focal brain disorders,
Derivatives of the EEG technique include evoked potentials (EP), which involves
averaging the EEG activity time-locked to the presentation of a stimulus of some
sort (visual, somatosensory, or auditory).
Event-related potentials (ERPs) refer to averaged EEG responses that are time-
locked to more complex processing of stimuli; this technique is used in cognitive
science, cognitive psychology, and psychophysiological research.
 Electroencephalogram (EEG)

Introduction
Invented by Hans Berger (Germany)
EEG measures the potential fluctuations recorded from the brain
Electrode types:

Significance:
The recordings represent a superposition of the field potentials produced by
a variety of active neuronal current generators within the volume conductor
medium.
Neurons have complex interconnections and thus EEG interpretation is not
very simple
Architecture of neuronal brain tissue is not uniform
Types of Brain Signal
Brainstem
 Brainstem

Overview:
The oldest and most primitive region of the brain. Includes white and gray
matter.
Contains: (1) midbrain, (2) medulla oblongata, (3) pons.
Major Functions:
Midbrain: Eye movement
Pons:
Relay station between cerebrum and cerebellum
Coordination of breathing
Medulla oblongata: control of involuntary functions.
Reticular formation (not anatomically well defined): arousal, sleep, muscle
tone, pain modulation.
Key point:
Brainstem damage is a very serious and often life-threatening problem.
 Functions of different parts of the brain
Functions of Cerebrum:
Cerebral cortex
Sensory areas: perception.
Motor areas: skeletal muscle movement.
Association areas: integration of information and direction of voluntary
movement.
Basal ganglia: movement [Ch. 13]
Limbic system
Amygdala: emotion, memory
Hippocampus: learning, memory.
Functions of Cerebellum:
Process sensory information and coordinate movement (inner ear, balance)
Functions of Diencephalon
Thalamus: integrating and relay station for sensory and motor information
Pineal gland: melatonin secretion.
Hypothalamus: Homeostasis, behavioral drives.
Pituitary gland: hormone secretion.
 Origin of EEG

General features of cortical architecture

Stratified layers containing cell bodies and fiber bundles
An outermost layer that lacks neurons (Layer I)
Inner layer containing neurons that give rise to large dendrites that rise
vertically
Human cortex is arranged in six such layers.
Pyramidal cell (Fig.):
Found in the cerebral cortex, the hippocampus, and the amygdala.
Bodies of these cells are triangular in shape
Have long axons and are perpendicular to the cortex
They are multipolar neurons
Graded Potential
 Origin of EEG (Cont.)

Field potential due to non-pyramidal cells:

Do not contribute significantly to surface EEG.
Axons are not always parallel to each other, their effect on the surface EEG
is not significant.
Field potential due to pyramidal cells:
Long apical dendrites run parallel to one another. Vertical to the cortex.
Similarly oriented & densely packed units form outer layers of the cortex.
For excitatory input
creates a potential sink (-ve charge).

membrane.
Sub-
the synaptic site (current loop) through the bathing medium.
This loop current causes surface potential to be picked up by the EEG scalp
electrode
 EEG Waves

Type Freq. Location Significance

(Hz)

Alpha 8 - 13 Mostly in occipital Awake and resting state. When

region, also parietal & focused alpha is replaced by
frontal region asynchronous waves of lower
amplitude
Beta 14-30 Mainly parietal & Beta I (high): Behave similar to
frontal region alpha.
Beta II (low): Intense mental
activity, tension.
Theta 4-7 Mainly parietal & Emotional stress (disappointment
temporal region and frustration).
(children)
Delta <3.5 Not dominated in a Deep sleep, infancy or organic brain
specific region disease
 EEG Waves
The EEG is typically described in terms of
Rhythmic activity
Transients
The rhythmic activity is divided into bands by frequency

A typical single-electrode EEG for 1 second

Most of the cerebral signal observed in the scalp EEG falls in the range of 1 20 Hz
(activity below or above this range is likely to be artifactual, under standard clinical
recording techniques).
Waveforms are subdivided into bandwidths known as delta, theta, alpha, beta, and
gamma to signify the majority of the EEG used in clinical practice.
 EEG Waves
Delta waves Hz. It tends to be the highest in
amplitude and the slowest waves. It is seen normally in adults in slow wave sleep. It
is also seen normally in babies. It may occur focally with subcortical lesions and in
general distribution with diffuse lesions, metabolic encephalopathy hydrocephalus or
deep midline lesions. It is usually most prominent frontally in adults and posteriorly
in children.
 EEG Waves
Theta waves Hz to 7 Hz. Theta is seen
normally in young children. It may be seen in drowsiness or arousal in older children
and adults; it can also be seen in meditation. Excess theta for age represents
abnormal activity. It can be seen as a focal disturbance in focal subcortical lesions; it
can be seen in generalized distribution in diffuse disorder or metabolic
encephalopathy or deep midline disorders or some instances of hydrocephalus. On
the contrary this range has been associated with reports of relaxed, meditative, and
creative states.
 EEG Waves
Alpha waves: Alpha is the frequency range from 7 Hz to 14 Hz. This is the
"posterior basic rhythm" (also called the "posterior dominant rhythm" or the
"posterior alpha rhythm"), seen in the posterior regions of the head on both sides,
higher in amplitude on the dominant side. It emerges with closing of the eyes and
with relaxation, and attenuates with eye opening or mental exertion. The posterior
basic rhythm is actually slower than 8 Hz in young children (therefore technically in
the theta range).
 EEG Waves
Beta waves Hz to about 30 Hz. It is seen
usually on both sides in symmetrical distribution and is most evident frontally. Beta
activity is closely linked to motor behavior and is generally attenuated during active
movements. Low amplitude beta with multiple and varying frequencies is often
associated with active, busy or anxious thinking and active concentration. Rhythmic
beta with a dominant set of frequencies is associated with various pathologies and
drug effects, especially benzodiazepines. It may be absent or reduced in areas of
cortical damage. It is the dominant rhythm in patients who are alert or anxious or
who have their eyes open.
 EEG Waves
Gamma waves: Gamma is the frequency range approximately 30 100 Hz.
Gamma rhythms are thought to represent binding of different populations of neurons
together into a network for the purpose of carrying out a certain cognitive or motor
function.
 EEG Waves
Sensorimotor rhythm aka mu rhythm: In addition to the posterior basic rhythm,
there are other normal alpha rhythms such as the mu rhythm that emerges when the
hands and arms are idle. Alpha can be abnormal; for example, an EEG that has
diffuse alpha occurring in coma and is not responsive to external stimuli is referred to
as "alpha coma". Mu ranges 8 13 Hz and partly overlaps with other frequencies. It
reflects the synchronous firing of motor neurons in rest state. Mu suppression is
thought to reflect motor mirror neuron systems, because when an action is observed,
the pattern extinguishes, possibly because of the normal neuronal system and the
mirror neuron system "go out of sync", and interfere with each other.
Clinical EEG: 10-20 System
Electrode Placement
 Clinical EEG System
The 10-20 System
Uses certain anatomical landmarks to standardize placements of EEG
electrodes
Representation of EEG channels is referred to a montage.

Type of Montage Channel measurement

Bipolar montage Difference between two adjacent electrodes

Referential Difference between one electrode & a reference electrode

montage (e.g. ear)

Average reference Difference between one electrode and the average of all
montage other electrodes

Laplacian Difference between one electrode & a weighted average of

montage surrounding electrodes
 Normal EEG

Normal EEG by 20-40 system

 Abnormal EEG
Epilepsy
Epilepsy is a central nervous system (neurological) disorder in which brain
activity becomes abnormal, causing seizures or periods of unusual
behavior, sensations, and sometimes loss of awareness.
EEG can be used to diagnose different types of epilepsy and location of the
focus in the brain causing the epilepsy
Epilepsy results in uncontrolled excessive activity in some parts of the CNS
 Electromyogram (EMG)
An electromyogram (EMG) is the graphical representation of electrical potential
generated by muscle cells when these cells are electrically or neurologically
activated. The signals can be analyzed to detect medical abnormalities, activation
level, or recruitment order or to analyze the biomechanics of human or animal
movement. Electromyography is an electrodiagnostic technique for evaluating and
recording the electrical activity produced by skeletal muscles.

The electrical source is the muscle membrane potential of about 90 mV. Measured
EMG potentials range between less than 50 and up to 20 to 30 mV, depending
on the muscle under observation. Typical repetition rate of muscle motor unit firing
is about 7 20 Hz, depending on the size of the muscle, previous axonal damage and
other factors. Damage to motor units can be expected at ranges between 450 and
780 mV.
EMG

A typical EMG
EMG

Muscle contraction resulting EMG

 EMG
There are two kinds of EMG:
i. Surface EMG and
ii. Intramuscular EMG

Surface EMG assesses muscle function by recording muscle activity from the
surface above the muscle on the skin. Surface electrodes are able to provide only a
limited assessment of the muscle activity. Surface EMG can be recorded by a pair
of electrodes or by a more complex array of multiple electrodes. More than one
electrode is needed because EMG recordings display the potential difference
between two separate electrodes.

Limitations of this approach are the fact that surface electrode recordings are
restricted to superficial muscles, are influenced by the depth of the subcutaneous
tissue at the site of the recording which can be highly variable depending of the
weight of a patient, and cannot reliably discriminate between the discharges of
adjacent muscles.
 EMG
Intramuscular EMG can be performed using a variety of different types of
recording electrodes. The simplest approach is a monopolar needle electrode. This
can be a fine wire inserted into a muscle with a surface electrode as a reference; or
two fine wires inserted into muscle referenced to each other. Most commonly fine
wire recordings are for research or kinesiology studies. Diagnostic monopolar EMG
electrodes are typically stiff enough to penetrate skin and insulated, with only the tip
exposed using a surface electrode for reference. Needles for injecting therapeutic
botulinum toxin or phenol are typically monopolar electrodes that use a surface
reference, in this case, however, the metal shaft of a hypodermic needle, insulated
so that only the tip is exposed, is used both to record signals and to inject.
EMG
Motor Units in Skeletal Muscle
 Electroneurogram (ENG)
Electroneurogram is a method used to visualize directly recorded electrical
activity of neurons in the central nervous system (brain, spinal cord) or the
peripheral nervous system (nerves, ganglions).
An ENG is usually obtained by placing an electrode in the neural tissue.
The electrical activity generated by the neurons is recorded by the electrode and
transmitted to an acquisition device where ENG may be visualized.
Each vertical line in an ENG represent an action potential.
An ENG signal may capture the activity of a single neuron or thousands
depending on the precision of of the electrode.
Used for assessing neuromuscular disorders, peripheral nerve injury, muscular
dystrophy.
Electrocorticography (ECoG) uses electrodes placed directly on the exposed
surface of the brain to record electrical activity from the cerebral cortex.
Electroencephalography (EEG) monitor this activity from outside the skull
using surface electrodes.
In some books: ECoG & EEG are considered types of ENGs
 Electroretinogram (ERG)
The electroretinogram (ERG) is a diagnostic test that measures the electrical activity
generated by neuronal and non-neuronal cells in the retina in response to a light stimulus.
The electrical response is a result of a retinal potential generated by light-induced changes in
the flux of transretinal ions, primarily sodium and potassium. Most often, ERGs are obtained
using electrodes embedded in a corneal contact lens, which measure a summation of retinal
electrical activity at the corneal surface. The ERG can provide important diagnostic
information on a variety of retinal disorders including, but not limited to congenital
stationary night blindness, Leber congenital amaurosis and cancer-associated
retinopathy. Moreover, an ERG can also be used to monitor disease progression or
evaluating for retinal toxicity with various drugs or from a retained intraocular foreign body.

Maximal response ERG

waveform from a dark
adapted eye
 ERG Waves
a-wave: initial corneal-negative deflection, derived from the cones and rods of the outer
photoreceptor layers. This wave reflects the hyperpolarization of the photoreceptors due to
closure of sodium ion channels in the outer-segment membrane. Absorption of light triggers
the rhodopsin to activate transducin, a G-protein. This leads to the activation of cyclic
guanosine monophosphate phosphodiesterase (cGMP PDE) eventually leading to a reduction
in the level of cGMP within the photoreceptor. This leads to closure of the sodium ion
channels resulting in a decrease of inwardly directed sodium ions, or a hyperpolarization of
the cell. The a-wave amplitude is measured from baseline to the trough of the a-wave.

b-wave: Corneal-positive deflection; derived from the inner retina, predominantly Muller and
ON-bipolar cells. The hyperpolarization of the photoreceptor cells results in a decrease in the
amount of neurotransmitter released, which subsequently leads to a depolarization of the post-
synaptic bipolar cells. The bipolar-cell depolarization increases the level of extracellular
potassium, subsequently generating a transretinal current. It is this transretinal current that
depolarizes the radially oriented Muller cells and generates the corneal-positive deflection.
The b-wave amplitude is generally measured from the trough of the a-wave to the peak of the
b-wave. This wave is the most common component of the ERG used in clinical and
experimental analysis of human retinal function.
 ERG Waves
c-wave: derived from the retinal pigment epithelium and photoreceptors. The c-wave
is a reflection of the resulting change in the transepithelial potential due to the
hyperpolarization at the apical membrane of the RPE cells and the hyperpolarization
of the distal portion of the Muller cells. The c-wave generally peaks within 2 to 10
seconds following a light stimulus, depending on flash intensity and duration. Due to
the c-wave response developing over several seconds, it is susceptible to influences
from electrode drift, eye movements, and blinks

Latency of response refers to the onset of the stimulus to the beginning of the a-
wave.
Implicit time is a measure of the time interval from onset of the stimulus to the
peak of the b-wave.
 Electrooculogram (EOG)
Electrooculogram (EOG) is the corneo-retinal standing potential that exists
between the front and the back of the human eye. Primary applications are in
ophthalmological diagnosis and in recording eye movements. Unlike the ERG,
the EOG does not measure response to individual visual stimuli. To measure eye
movement, pairs of electrodes are typically placed either above and below the eye
or to the left and right of the eye. If the eye moves from center position toward one
of the two electrodes, this electrode "sees" the positive side of the retina and the
opposite electrode "sees" the negative side of the retina. Consequently, a potential
difference occurs between the electrodes. Assuming that the resting potential is
constant, the recorded potential is a measure of the eye's position.
EOG

EOG for the period of REM sleep