Nerve Conduction Study (NCV)
An electrical test used to detect nerve conditions.
In the nerve conduction velocity (NCV) test, the nerve is electrically stimulated by one electrode while other electrodes detect the electrical impulse "down stream" from the first electrode.
The NCV test is usually done with surface patch electrodes similar to those used for an EKG (electrocardiogram).
The patch electrodes are placed on the skin over the nerve at various locations.
One electrode stimulates the nerve with a very mild electrical impulse.
The resulting electrical activity is recorded by the other electrodes.
The distance between electrodes and the time it takes for electrical impulses to travel between electrodes are used to calculate the speed of impulse transmission (the nerve conduction velocity, or NCV).
A decreased speed of nerve conduction indicates nerve disease.
The interpretation of an abnormal NCV test depends on why the test was done in the first place.
It may indicate damage to a nerve from trauma, polio, diabetic neuropathy (nerve damage), a herniated disc, myasthenia gravis, Guillian-Barre Syndrome, Polyneuropathy (the simultaneous malfunction of many nerves) and many other conditions.
The patient having a NCV test lies on an examination table.
The electrodes are placed on the skin over the nerve to be studied.
An electrical stimulator is then placed on the skin near the electrodes and is used to create an electrical current strong enough to fully stimulate the nerve.
A computer is used to record responses as various nerves are tested.
Value of Neurophysiological Tests:
- Improve patient's care by providing objective information that could lead to therapeutic decisions that will result in more successful treatment
- Provide objective information to increase accuracy of the prognosis
- Documentation to support patient care
While the range of potential neurodiagnostic testing is extensive, one of the mainstays of neurodiagnostics remains the EMG/NCV test - which stands for Electromyography and Nerve Conduction testing.
The first documented experiments dealing with EMG started with Francesco Redi's works in 1666.
Redi discovered a highly specialized muscle of the electric ray fish (Electric Eel) generated electricity.
By 1773, Walsh had been able to demonstrate that the Eel fish's muscle tissue could generate a spark of electricity.
In 1792, a publication entitled "De Viribus Electricitatis in Motu Musculari Commentarius" appeared, written by Luigi Galvani, in which the author demonstrated that electricity could initiate muscle contractions.
Six decades later, in 1849, Dubios-Raymond discovered that it was also possible to record electrical activity during a voluntary muscle contraction.
The first actual recording of this activity was made by Marey in 1890, who also introduced the term electromyography.
In 1922, Gasser and Erlanger used an oscilloscope to show the electrical signals from muscles.
Because of the stochastic nature of the myoelectric signal, only rough information could be obtained from its observation.
The capability of detecting electromyographic signals improved steadily from the 1930s through the 1950s, and researchers began to use improved electrodes more widely for the study of muscles.
Clinical use of surface EMG (sEMG) for the treatment of more specific disorders began in the 1960s.
Hardyck and his researchers were the first (1966) practitioners to use sEMG.
In the early 1980s, Cram and Steger introduced a clinical method for scanning a variety of muscles using an EMG sensing device.