In nerve conduction studies, the speed of nerve impulses is slower than normal for that nerve. Examples include a herniated disc, amyotrophic lateral sclerosis (ALS), and inflammation. Abnormal wave lines when a muscle contracts may mean there is a muscle or nerve problem. They generally get slower as a person gets older.įor an EMG, electrical activity in a muscle at rest shows that there may be a problem with the nerves used by the muscle.
Not all nerves have the same normal conduction velocities.
Sensory nerves allow the brain to feel pain, touch, temperature, and vibration. The nerve conduction studies show that the nerves send electrical impulses to the muscles or along the sensory nerves at normal speeds, or conduction velocities. There is a smooth, wavy line on the recording with each muscle contraction. The EMG recording shows no electrical activity when the muscle is at rest. Electromyogram (EMG) and nerve conduction studies Your doctor may be able to tell you some of the results of your nerve studies right after the tests. It depends on how many nerves and muscles your doctor tests. Nerve conduction tests may take from 15 minutes to 1 hour or more.Nerve conduction studies are done before an EMG if both tests are being done. When the test is over, the electrodes are removed. The results from both sides of the body can be compared. The same nerves on the other side of the body may be studied. The speed of the response is called the conduction velocity. The time it takes for the muscle to contract in response to the electrical pulse is recorded. Several quick electrical pulses are given to the nerve. Then a recording electrode is placed over the muscles controlled by that nerve. An electrode that puts out electric pulses is placed right over the nerve.
In this test, several flat metal-disc electrodes are attached to your skin with tape or a paste. The places where a needle was put in the skin are cleaned. When the test is done, the electrodes are removed. The activity may also be recorded on video. You may hear popping sounds like a machine gun when you contract the muscle. The electrical activity in the muscle is shown as wavy and spiky lines on a video screen. This is done to record the activity in different parts of the muscle or in different muscles. The electrode may be moved a number of times. Then the technologist or doctor asks you to tighten (contract) the muscle slowly and steadily. When the electrodes are in place, the electrical activity in that muscle is recorded while the muscle is at rest. The electrode is attached by wires to a recording machine. The skin over the areas being tested is cleaned. Or you may sit in a chair that leans back so your muscles are relaxed. You will be asked to lie on a table or bed. It may be done in a room that stops any outside electrical activity that can interfere with the test. An EMG is done in a hospital, a clinic, or a doctor's office.
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