What is a jitter in EMG?

2020-10-09 Kobe Glover

What is a jitter in EMG?

Jitter is expressed as the mean of the absolute consecutive differences (MCD) of the latency between the time-locked potentials (volitional SFEMG) or from the stimulus to the negative peak of the potential (stimulated SFEMG). Recording is judged abnormal when more than 10% of the collected pairs are abnormal.

What is a neuromuscular jitter?

When the SFEMG electrode is positioned to record from 2 or more muscle fibers in one voluntarily activated motor unit, the neuromuscular jitter is seen as variations in the time intervals between pairs of APs from these fibers (see images below). This paired jitter represents the combined jitter in 2 endplates.

How is single fiber EMG performed?

Electrode setup for single-fiber electromyography (SFEMG) during intramuscular axonal stimulation. The stimulating electrode is inserted into the muscle near an intramuscular nerve fiber, and the recording electrode is inserted distally near muscle fibers innervated by this nerve.

Does a single fiber EMG hurt?

Yes. There is some discomfort at the time the needle electrodes are inserted. They feel like shots (intramuscular injections), although nothing is injected during an EMG. Afterwards, the muscle may feel a little sore for up to a few days.

What does an EMG look for?

Electromyography (EMG) measures muscle response or electrical activity in response to a nerve’s stimulation of the muscle. The test is used to help detect neuromuscular abnormalities. During the test, one or more small needles (also called electrodes) are inserted through the skin into the muscle.

What does an abnormal EMG sound like?

The sound of positive sharp waves have been described as, like ‘claps of distant thunder’, and fibrillation potentials a higher pitched and shorter duration sound, like ‘rain on a tin roof’.

What is muscle jitter?

Jitter is the measurement of variation of the inter-potential interval. This is calculated between the triggered potential and the time-locked, second single muscle fiber action potential [Figures 4–7]. This is expressed as a mean consecutive difference (MCD).

Who invented electromyography?

Six decades later, in 1849, Emil du Bois-Reymond 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.

How long does a single fiber EMG take?

Important Note: The small size of the needle means that it should not be too uncomfortable. As with all needles, this can sometimes leave a bruise and the muscles may feel sore for a while after the test. The entire test may take up to 90 minutes.

What is the neuromuscular jitter in single fiber EMG?

When does jitter increase in a SFEMG study?

Jitter increases slightly with age in normal subjects. A study is abnormal if the mean (or median) jitter exceeds the upper limit for the muscle, or if more than 10% of pairs or endplates have increased jitter or blocking. Jitter less than 5 µs is seen rarely in voluntarily activated SFEMG studies in normal muscles and more often in myopathies.

What are the different settings for measuring jitter?

Equipment settings for measuring jitter • LF Filter: to remove distant signals o SFEMG electrode – 500 Hz o CN electrode – 1000 Hz • Gain – typically 0.2 -0.5 mV/div (to see signals clearly) • Sweep – typically 0.5 ms/div (to see jitter & late components) • Signal triggered delay – to show components before and after the trigger point

How does jitter affect the performance of a computer?

Jitter can cause a display monitor to flicker, affect the performance of processors in personal computers, introduce clicks or other undesired effects in audio signals, and cause loss of transmitted data between network devices. The amount of tolerable jitter depends on the affected application.