Basic Nerve Conduction Study Flashcards
The recorded potential from motor conduction study is called….
CMAP (Compound Muscle Action Potential)
Describe the concept of CMAP (Compound Motor Action Potential)!
CMAP represent the summation of all underlying individual muscle fiber potentials.
Name the parameters measured when assesing CMAP!
For each stimulation, the latency, amplitude, duration, and area of the CMAP are measured. Motor conduction velocity can be calculated after two sites, one proximal and one distal, have been stimulated.
Explain CMAP latency!
Latency: the time from the simulus to the initial CMAP deflection from baseline.
Latency represents 3 separate processes: 1) the nerve conduction from the stimulus to NMJ (neuromuscular junction), 2) the time delay across the NMJ, 3) the depolarization time across the muscle.
Latency reflects only the fastest conducting fibers.
Explain CMAP amplitude!
CMAP amplitude is most commonly measured from baseline to the negative peak. Less commonly it can also be measured from the first negative peak to the next positive peak.
It reflects the number of muscle fibers that depolarize.
Low CMAP amplitude most often result from loss of axons. Other causes include conduction block from demyelination, NMJ disorder, and myopathies.
Explain CMAP area!
CMAP area is calculated from the area under the curve of negative peak CMAP. It reflects the number of muscle fibers that depolarize.
Explain CMAP duration!
CMAP duration is measured from the initial deflection to the first baseline crossing (preferred). It can also be measured from the initial deflection to the terminal deflection back to baseline.
Duration is a measure of synchrony (the extent to which each of the individual muscle fibers fire at the same time).
Characteristically increases in condition that result in slowing of some motor fibers but not others (eg. in demyelinating lesion)
