This tests the peripheral nervous system of the arms and legs by evaluating the motor fibers. Motor NCV tests are performed using adhesive surface electrodes to record the compound action potentials generated following stimulation with electric current (a very short duration pulse about 0.1 ms) at two or more points of the main trunk of the motor nerve and recording the latencies at a distal muscle supplied by the nerve.
Also evaluates the peripheral nervous system of the arms and legs. The sensory fibers and the conduction of the sensory nerves are evaluated using the same surface electrodes of the Motor NCV in differing montages to record the sensory nerve potentials after stimulation by an even shorter duration pulse (0.05 ms) of electric current at a region of the sensory nerve. The recording can be done either orthodromically or antidromically to best evaluate the nerve being studied.
F waves determine the proximal conduction of the motor nerve to the spinal cord. It is obtained by supramaximal stimulation of the motor nerve and recording the antidromic activation of the motor neurons in the spinal cord that discharged back to the same motor nerve. Surface electrodes applied to a distal muscle record this activity. The F wave latency is obtained from an evaluation of multiple responses.
The H-reflex, also known as the Hoffmann reflex, evaluates the proximal conduction to the spinal cord like F-waves but is performed in a different format and yields further, more specialized data. Unlike F-waves, H-reflexes are considered true reflexes and are composed of a sensory afferent, a synapse, and a motor efferent segment.
They are obtained through sub-maximal activation of a compound nerve, such as the Tibial or Median, with stimulation of the large size Ia afferent sensory fibers that give rise to a reflex response with activation of the Alpha motor neuron and subsequent contraction of a distal muscle innervated by the activated neuron. This activity is recorded by surface electrode applied over the distal muscle. The H-reflex latency is also obtained from multiple responses. This test is identical in respect to a deep tendon reflex, although it is electrically elicited instead of being mechanically elicited through the use of a reflex hammer.