Search

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 D(1), D(2) 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 (MR(2)) (giving the same estimated value as MCD), Mean Range of Five (MR(5)), Mean Range of Ten (MR(10)) and also from the Standard Deviation (SD). In a distribution without trends the following relations hold:MCD = 1·13×SDMCD = 0·49×MR(5)MCD = 0·37×MR(10)·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.

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.

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 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.

This paper describes a system for automatized measurements of time intervals between single fiber action potentials, the recording of measurement data on magnetic tape, the administrative system for handling data and some computer programs for calculations. The paper is intended to give a general description of an experimental system, where computer treatment of data is one essential part.

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.