Clinical Electro Physiological Testing
Clinical Electro Physiological Testing
Clinical Electro Physiological Testing
These measures give information about both motor and sensory components
of the peripheral nervous system. They also suggest whether the axon or the
myelin sheath of nerves is more damaged by a neuropathy. Myelin helps
action potentials travel faster, and so in problems of myelin (myelinopathies),
conduction velocity is more decreased. In problems with the axon
(axonopathies), fibers that are intact can conduct signals at normal speeds,
but there are fewer fibers, which leads to a weaker signal and decreased
amplitude.
When an EMG is performed, electrical activity from muscle fibers is
measured and demonstrated as waves on a screen and static-like noises
played on a speaker.
The technician listens to these sounds and watches the monitor in order to
detect abnormalities.
In contrast, MUPS are abnormally small or brief, and suggest the presence
of a disease of a muscle (amyopathy ).
Interpreting EMG results may also mention the term "recruitment pattern."
As a muscle is contracted, nerve fibers signal more and more bits of muscle
(called motor units) to join in and help. In a neuropathic disorder, the
amplitude of different motor units is strong, but there are fewer of them
because the nerve is unable to connect to as many units. In myopathies, the
number of motor units is normal, but the amplitude is smaller.
The pattern of electrical discharges from the muscle can give additional
information as to the cause of the problem, and may even help determine
how long a problem has been present.
NERVE CONDUCTION STUDIES
The electrical signal sent along the axon of a nerve is called an action potential.
In nerve conduction studies, these action potentials are artificially generated by
electrical stimulation in order to assess how the axon responds.
There are two main portions to a nerve conduction study: sensory and motor.
Recording from a sensory nerve gives a sensory nerve action potential (SNAP),
and recording from a muscle yields a compound muscle action potential
(CMAP).
It assess peripheral motor and sensory nerve function by
recording the evoked potential generated by electrical
stimulation of a peripheral nerve.
The CMAP evoked from the APB appears later on the display
screen, and the longer latency is recorded as L2.
It is easier to record.
Extreme swelling
Abnormal blood clotting
Dermatitis
Uncooperative patient
Recent myocardial infarction
Blood-transmittable disease
Immune-suppressed condition
Pacemakers
Hypersensitivity to stimulation
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