Transcript In The Name of Allah The Most Beneficent The

IN THE NAME OF ALLAH
THE MOST BENEFICENT THE MOST MERCIFUL
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ECE 4552:
MEDICAL
ELECTRONICS
LECTURE:
ELECTRO-MYO
GRAM (EMG)
Engr. Ijlal Haider
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Electrical Engineering Dept.
University of Lahore, Lahore
TYPES OF NERVES

Sensory Nerves


Nerves that carry information from sensory parts to
the brain
Motor Nerves

Nerves that carry information from brain to
actuating parts
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TYPES OF NERVES
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MOTOR UNITS
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ELECTROMYOGRAM
Greek words
 MYOS-Muscle
 GRAM-Picture
 Picture of Electrical Activities of Muscles

STIMULUS

Voluntary (under willful action of brain)
Not good for diagnosis of muscle disorders which has
to be diagnosed early
 Impulses travel in only one direction


Evoked (on artificial stimulation)

Impulses travel in both directions
EMG
Using Skin Surface electrodes
 Using Needle electrodes

Monopolar
 Bipolar

MEASUREMENT OF POTENTIAL DIFFERENCE

How do we get a potential difference between two
points outside a muscle fiber (or a nerve fiber??)
When Fully Polarized!!
 Partially Depolarized!!
 Fully Depolarized!!

MEASUREMENT OF POTENTIAL DIFFERENCE
When there is partially depolarization, ionic
current start flowing which gives rise to voltage
 In case of fully polarized or fully depolarized, no
current flows and hence we don’t get any voltage
out

SKIN SURFACE ELECTRODES
Compound or composite of Muscle Action
Potential from individual muscle fibers is
recorded
 Sometime called Interference Pattern
 Contribution from muscle fibers will depend on
the closeness and proximity to the electrodes
 We cannot make out much on the origin of these
signals
 We can only use it to find gross muscular
disorders


Which can already be felt by muscle weakness and
can be visually seen as wasted muscle
SKIN SURFACE ELECTRODES
Surface electrodes are not very much used for the
diagnosis of muscle disorders
 They are used majorly for evoked potential study
in

Nerve Conduction Velocity (NCV) measurement
 Physiotherapy or exercise (kind of mitigation or
relaxing)
 Another application is Bio-feedback for stroke
recovery

NEEDLE ELECTRODES

Monopolar





Similar to a coaxial
We use instrumentation (differential) amplifiers
Requires 3 probes
Active, Reference, Common
Common is taken from a skin surface electrode
NEEDLE ELECTRODES

Bipolar
In contrast to mono-polar electrodes, bipolar have
two electrodes inside and one outside
 Instrument amplifiers are used
 All three probes are taken from the bipolar needle
electrode itself
 Mostly used for research purpose

NEEDLE EMG
Used for diagnosis of muscle disorders
 Helps in localizing a focus of disorder

As injecting a pin (needle) inside skin is painful
and to diagnose properly multiple points are
needed, the whole process becomes very painful
 To reduce pain, insertion points are reduced and
in each points the angle of pin is changed without
bringing needle outside the skin (mostly 3 angles)

ANALYSIS OF EMG
Analysis is done empirically by doctors (clinical
experiences)
 Looks for EMG patterns when the needle is being
inserted
 Listens to the sound produced by feeding the
muscle signal into a loud speaker
 Also looks at the pattern and listens to the sound
on mild voluntary contraction

ANALYSIS OF EMG
Signal Processing in EMG
 For automated diagnosis, pattern recognition
techniques are being investigated
 Neural Networks, Genetic Algorithms and other
AI techniques are/can be used
 Old instruments used to have integrators

ANALYSIS OF EMG

Simple Block Diagram of EMG
EMG Amplifiers
 Filter
 Display
 Signal processing unit/ Intelligent Systems
 Audio amplifier

MEASUREMENT OF NCV
Using evoked potential
 Through artificial stimulation of nerve
 For example by giving a voltage of 100 volts for
very short time approximately 2 msec, hand
movements must be observed
 --fig. evoking an action potential using surface
electrodes

EVOKED POTENTIAL
Nothing happens under anode (+ve electrode)
 Reversal of trans-membrane potential occurs
under cathode (-ve electrode)
 This causes generation of an action potential
 Generated action potential travels along the
nerves in both directions

MEASUREMENT OF NCV

Similar to a sprint race where a stopwatch is
pressed on when runner starts and time is
recorded untill he reaches the finish line and
velocity is calculated from the distance travelled
and time, NCV is recoded by measuring the time
for nerve action potential to travel a distance “d”
from stimulation point to recording point
SENSORY NCV
Nerve stimulator applies stimulation through
ring electrodes at fingers
 Median Nerve contains both sensory and motor
nerves
 Recording site is selected near middle of arm

SENSORY NCV
Conventions
 Cathode of the stimulation electrodes is kept
near the recording side, so that action potential is
not perturbed by anode)
 Recording electrode which is towards the
stimulation side is connected to the inverting
input of the amplifier
 Common electrode is placed ideally at an
equidistant point from both electrodes (to have
min common mode voltage)

SENSORY NCV
--fig. stimulation pulse
 --fig. recording side, stimulation artifacts and
compounded action potential
 Latency of the pulse is recorded
 SNVC=d/∆t

MOTOR NCV
In contrast to SNCV measurement, MNCV
measurement involves stimulating at two sites
and recording at one
 For median nerve
 Stimulation sites

Wrist
 Elbow


Recording site

Thenar Muscle
MOTOR NCV
Why we stimulate on two sites?
 Neuromuscular junction has unknown delay
 Record latencies of proximal and distal
stimulation sites individually (let t1 and t2 be the
latencies of both respectively)
 Distance between both stimulation sites is taken
 --fig. MNVC signals
 MNCV=d/(t2-t1)

DIAGNOSIS AND DISEASES
If either SNCV or MNCV is significantly less
then normal values?
 Is the distal latency prolonged?

DIAGNOSIS AND DISEASES
Causes of low NCV
 Demyelination
 Conduction block
 Axonopathy

DIAGNOSIS AND DISEASES
Disorders
 Peripheral Neurotherapy
 Carpel Tunnel Syndrome (Wrist)
 GB Syndrome
 Cervical Spondylosis (Neck)
 Lumbo-Sacral Spondylosis (Waist)

EMG FOR PROSTHESIS
EMG signals are used to study the electrical
activities of muscles under certain movements
 EMG signals are picked up from certain points
and fed to the prosthetic limb or exoskeleton

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NERVE STIMULATOR
For a single pulse: Monostable Multi-vibrator
 For repetitive pulses: Astable Multi-vibrator

Amplitude required: 100-200 volts
 Pulse duration: less then 2msec

Peak current requirement near to 20 mA (max 50
mA)
 Power requirement (for peak power 300x50mA)

COMMONLY MEASURED


Upper limb, Median, Ulnar, Radial, Lower Limb,
Common Peroneal, Tibial
Class Activity
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THANK YOU!
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