Jan Ekstedt

Calculation of the electromyographic jitter.

The electromyographic jitter is the variability at consecutive discharges in the time interval between two action potentials from two muscle fibres from the same motor unit. This paper deals with different methods of expressing the jitter. The method of choice seems to be Mean Consecutive Difference (MCD) [Formula: see text] where D1, D2 etc. are the individual time interval measurement data and n the number of discharges, preferably 50 or, if the jitter is not changing, 200. MCD can also be estimated from other measures of the jitter like Mean Range of Two (MR2) (giving the same estimated value as MCD), Mean Range of Five (MR5), Mean Range of Ten (MR10) and also from the Standard Deviation (SD). In a distribution without trends the following relations hold: MCD = 1·13×SDMCD = 0·49×MR5MCD = 0·37×MR10· The presence of slow variations and trends in most recordings makes SD not well suited for calculation because of the risk of getting too high estimates of the jitter.

The electromyographic jitter in normal human muscles

Abstract The jitter ( i.e. , the variability in time interval at consecutive discharges between two action potentials from two muscle fibres belonging to the same motor unit) had been studied in four human muscles. The jitter, expressed as mean consecutive difference (MCD), was found to be: in m. biceps brachii: 15.7 ± 5.5 (SD) μ sec; in m. extensor dig. communis: 23.4 ± 8.5 μ sec; in m. frontalis: 19.1 ± 7.6 μ sec; and in m. tibialis anterior: 31.5 ± 12.4 μ sec. The jitter values were the same when recorded close to the end-plate zone or close to the tendon. There was no correlation between the mean inter-potential interval and the size of the jitter. At a very irregular innervation rate the jitter sometimes increased slightly, more often when recording was done close to the tendon than when close to the end-plate zone. However, the physiological unevenness of the innervation rate did not influence the jitter value. A decrease of the intramuscular temperature caused an increase of the jitter by 1–3 μsec/°C around 36°C.

Neuromuscular transmission in myasthenia gravis studied with single fibre electromyography

Patients with myasthenia gravis have been investigated with single fibre electromyography. In all myasthenic muscles recordings were obtained where there was an increase of the jitter and occasional blocking of different degree of single fibre action potentials. The jitter is the variability at consecutive discharges in the time interval between action potentials from two muscle fibres from the same motor unit. During prolonged activity the jitter increased and blockings occurred more and more frequently. The size of the jitter and the degree of blocking also depended on the discharge rate. At a low rate the jitter was lower and the degree of blocking less than at the high rate. Injection of edrophonium could decrease or increase the jitter or leave it unaffected. Single fibre electromyography is a sensitive way of studying the transmission in individual motor end-plates in myasthenia gravis and is also a valuable diagnostic aid.

How the size of the needle electrode leading-off surface influences the shape of the single muscle fibre action potential in electromyography.

Abstract The influence of the size of the leading-off surface on the shape of the extracellular single muscle fiber action potential has been studied with a digital computer simulation program. A 25 μ round leading-off surface has very little influence on the amplitude in comparison to what is obtained with a point-shaped electrode. The 580 μ × 150 μ leading-off surface in a concentric needle electrode considerably decreases the amplitude of action potentials from fibers close to the leading-off surface. Action potentials from more remote fibers, however, are not very much affected. This makes concentric needle electrodes not very well suited for single fiber electromyography.

Ischemic effects on impulse transmission to muscle fibers in man

Abstract Single fiber electromyography has been used to study the influence of ischemia on the impulse transmission to individual muscle fibers in man. The jitter (the variability in time interval between the action potentials from 2 muscle fibers belonging to the same motor unit) has been used to study the neuro-muscular transmission in individual motor end-plates. Ischemia increased the jitter and caused more and more frequent blocking of the neuromuscular transmission until total block occurred. About 3,500–7,000 impulses could be transmitted before total block developed. When circulation was restored, the formerly blocked potential reappeared within seconds and the jitter was normal within some minutes, even if ischemia had lasted for 30 min.

The construction of needle multi-electrodes for single fiber electromyography

Abstract This paper describes the construction of a needle multi-electrode in which fourteen 25 μ platinum leading-off surfaces are mounted in epoxy resin in an opening in the side of an injection needle, 0.5–0.6 mm in diameter.

The effect of non-paralytic doses of d-tubocurarine on individual motor end-plates in man, studied with a new electrophysiological method

Abstract The authors have used a new method for the study of synaptic transmission in individual motor end-plates in man. Single muscle fiber action potentials are recorded and the method is based upon the following principle: when two muscle fibers, belonging to the same motor unit, are recorded at the same time, there is always a variability in the time interval between the two action potentials for consecutive discharges. This variability, of 10–30 μsec, is called the jitter phenomenon and has been used in this investigation to study d -tubocurarine. It has been found that the jitter increases with doses of d -tubocurarine far below those required to give any neuromuscular block. With a dose of 15 μg/kg d -tubocurarine the jitter increased by 5–15 μsec from the normal. A dose of 30 μg/kg increased the jitter to more than 70 μsec, when occasional blocking occurred. This seems to be the first in situ method for obtaining quantitative information concerning synaptic transmission in individual motor end-plates in man.

Abnormal connections between skeletal muscle fibers

Abstract In two apparently healthy subjects EMG findings have been made of a type not previously encountered. The jitter between the muscle fiber action potentials from two different muscle fibers belonging to the same motor unit was only 2–3 μsec (S.D.), which is far less than that normally obtained (10–30 μsec). The jitter was unaffected by i.v. injection of 15 and 30 μg d -tubocurarine/kg body weight. Normally, a considerable increase of the jitter is seen at these doses. At the dose level 30 μg d -tubocurarine/kg, blocking of occasional discharges was seen, affecting both the fiber potentials simultaneously. Normally either one or the other of the two fiber potentials blocks in any one discharge. A hypothesis is presented whereby an abnormal connection existed between two or more fibers, so that activation of one fiber via its motor end-plate also activated the other fiber.

The jittermeter: A variability calculator for use in single fiber electromyography

Abstract A new instrument is described which calculates in “real time” the numerical value of the electromyographic jitter. With an accuracy of ±2% the instrument measures a variability of the order of some 10 μsec between two pulses, 0.1–25 msec apart.

IMPULSE TRANSMISSION TO MUSCLE FIBRES DURING INTRAVENOUS REGIONAL ANAESTHESIA IN MAN

The influence of intravenous regional anaesthesia on impulse transmission to muscle fibres was studied with single‐fiber electromyography during voluntary activity in man.