EEG (ElectroEncephaloGraph)
EEG (ElectroEncephaloGraph)
EEG (ElectroEncephaloGraph)
(ElectroEncephaloGraph)
Electroencephalograph is an instrument for recording the
electrical activity of the brain, by suitably placing surface
electrodes on the scalp.
EEG describing the general function of the brain activity, is
the superimposed wave of neuron potentials operating in a
non-synchronized manner in the physical sense.
Uses
Monitoring EEG is an effective method of diagnosing many
neurological illnesses and diseases like epilepsy, tumor,
cerebrovascular lesions, ischemia and problems associated
with trauma.
Also used in the operating room to facilitate anaesthetics
and to establish the integrity of the anaesthetized patient’s
nervous system.
Several types of electrodes may be used to record EEG like Peel and
Stick electrodes, Silver plated cup electrodes and Needle electrodes.
EEG may be recorded by picking up the voltage difference between
an active electrode on the scalp with respect to the reference
electrode in ear lobe or any part of body. This method is known as
Monopolar recording.
Needle electrode
Surface Electrodes
EMG is generally recorded using surface electrodes, which may be
disposable, adhesive or reusable types.
The electrodes pick up the potentials produced by contracting muscle
fibres.
The signal can be amplified and displayed on the screen of a cathode
ray tube or it is also applied to an audio amplifier connected to a loud
speaker.
A typical EMG ranges from 0.1 to 0.5mV and may contain frequency
components up to 10kHz.
Types of EMG
1) SURFACE ELECTROMYOGRAPHY (SEMG)
• Non-invasive technique for measuring muscle electrical activity resulting from
contraction and relaxation exercises.
2) FINE WIRE ELECTROMYOGRAPHY (INTRAMUSCULAR EMG)-
• Invasive technique for measuring muscle electrical activity resulting from
contraction and relaxation exercises.
3) NEUROMUSCULAR ELECTRICAL STIMULATION (NMES)
• Burst of electrical pulses stimulate muscle contractions in targeted muscles via
electrodes.
4) EMG-TRIGGERED STIMULATION (ETS)
• ETS is a combination of two complementary EMG modalities: SEMG and NMES.
Uses
EMG allows us to look at the electrical activity responsible for
muscle contractions and allows us to measure muscular
performance.
EMG has well established value as an evaluation tool used in applied
research, physiotherapy, rehabilitation, sports medicine and training,
biofeedback, and ergonomics research.
Practical medical applications involves EMG use in pre/post surgical
assessment and treatment, prevention or retardation of muscle
atrophy, increasing local blood circulation, relaxation of muscle
spasms, maintaining or increasing range of motion, and muscle re-
education and rehabilitation through biofeedback.
NCV (Nerve Conduction
Velocity test)
A Nerve Conduction Velocity (NCV) test , also called a Nerve
Conduction Study (NCS)--is a measurement of the speed of conduction
of an electrical impulse through a nerve. NCS can determine nerve
damage and destruction.
During the test, the nerve is stimulated, usually with surface electrode
patches attached to the skin. Two electrodes are placed on the skin
over the nerve.
One electrode stimulates the nerve with a very mild electrical impulse
and the other electrode records it. The resulting electrical activity is
recorded by another electrode.
This is repeated for each nerve being tested.
The nerve conduction velocity (speed) is then calculated by measuring
the distance between electrodes and the time it takes for electrical
impulses to travel between electrodes.
Need of NCV
I. In general, the range of normal conduction velocity in nerve will be
approximately 50 to 60 meters per second. However, the normal
conduction velocity may vary from one individual to another and from
one nerve to another.
II. Abnormal results may be caused by some sort of neuropathy (damage
to the nerve) that can result from a contusion or traumatic injury to a
nerve. Various diseases can also cause the impulses to slow down.
III. Nerve conduction velocity is often used along with an EMG to
differentiate a nerve disorder from a muscle disorder. NCS detects a
problem with the nerve whereas an EMG detects whether the muscle
is functioning properly in response to the nerve's stimulus.
IV. Both procedures help to detect the presence, location, and extent of
diseases that damage the nerves and muscles.
Sciatic nerve problems
Pinched nerves
Peripheral nerve injury
Nerve conduction studies may also be performed to identify the
cause of symptoms such as numbness, tingling, and continuous
pain.
• Guillain-Barré syndrome. A condition in which the body's immune system
attacks part of the peripheral nervous system. The first symptoms may
include weakness or tingling sensations in the legs.
• Carpal tunnel syndrome. A condition in which the median nerve, which runs
from the forearm into the hand, becomes pressed or squeezed at the wrist by
enlarged tendons or ligaments. This results in pain and numbness in the
fingers.
• Charcot-Marie-Tooth disease. A hereditary neurological condition that affects
both the motor and sensory nerves. One characteristic is weakness of the
foot and lower leg muscles.
• Herniated disk disease
• Chronic inflammatory polyneuropathy and neuropathy. These are conditions
resulting from diabetes or alcoholism.
Procedure
A neurologist will locate the nerve(s) to be studied.
A recording electrode will be attached to the skin over the nerve with
a special paste and a stimulating electrode will be placed at a known
distance away from the recording electrode.
The nerve will be stimulated by a mild and brief electrical shock given
through the stimulating electrode.
Patient may experience minor discomfort for a few seconds.
The stimulation of the nerve and the detected response will be
displayed on an oscilloscope (a monitor that displays electrical activity
in the form of waves).