Axonal stimulation for end-plate jitter studies.

Abstract

SUMMARY This single fibre EMG study compares the standard method of neuromuscular jitter measurement in voluntarily activated muscle to that by intramuscular electrical stimulation of motor axons in a group of normal subjects. The latter method avoids the interdischarge intervaldependent jitter, as well as a possible failure to recognise split muscle fibres. The mean MCD on axonal stimulation was only 5-2 ps less than in the voluntary activation study and was thus 8% more than theoretically expected for single motor end plates. The difference could be due to an axonal jitter and some other factors. Axonal stimulation has proved to be a relatively easy and reliable method for routine estimation of neuromuscular jitter, provided that the resolution of time measurement is better than 2 ps, so that low jitter due to occasional direct muscle fibre stimulation is not mistaken for a normal reading. The upper normal limits for the extensor digitorum communis muscle suggested by the present study are 40 ps (individual muscle fibres) and 25 ps (mean of 30 muscle fibres).In single fibre electromyography, the jitter of the motor end plates is usually measured during slight voluntary contraction of the muscle. This however, is not always practicable, for example in unco-operative or unconscious patients, young children and even in severely paretic muscles, whether there is an upper motor neuron lesion or very severe myasthenia gravis or weakness due to some other peripheral pathology. Electrical stimulation has been suggested for such cases and has actually been used in research,' but only seldom in clinical practice. Some of the reasons have been lack of relevant experience, the need for a high resolution jittermeter to eliminate the possibility of mistaking the low jitter due to direct muscle fibre stimulation for a normal reading, and unavailability of normal data. The purpose of this work was to collect normal values and compare the technique to the well established method with voluntary activation. Material and methodFifteen normal volunteers participated in the study. Their

The effects of anticholinesterases on the latencies of action potentials in mouse skeletal muscles

“…This variability may be in the time between APs of two fibres of the same motor unit in voluntary activity (Stalberg & Trontelj, 1979), or in the time between stimuli and APs in a fibre during a train of evoked responses (Trontelj et al, 1986). Excessive jitter is found in patients with muscular dystrophy or with myasthenia gravis, or after drugs (e.g.…”

Neurophysiological strategies for the diagnosis of disorders of the neuromuscular junction in children

“…To get around this problem they devised a technique in which the most distal motor nerve fibres could be stimulated in the muscle and the muscle fibre potentials recorded with the standard needle used for SFEMG. [21][22][23][24] The stimulation is effected by a monopolar needle acting as the active electrode, sometimes with another as the indifferent electrode but more commonly with a surface electrode fulfilling that role. Although the application of the technique in the intensive care unit might have been the stimulus to its invention, its obvious advantages in the investigation of children were quickly realized.…”

Análise do jitter com agulha concêntrica em pacientes com miastenia gravis autoimune adquirida

“…Essa diferença é menor do que em comparações similares com a AFU (Trontelj et al, 1986) e, provavelmente, reflete as dificuldades técnicas de registros com a AC, por causa do registro de PAs somados e valores subestimados de jitter (Kouyoumdjian, Stålberg, 2008b).…”

“…O tempo de transmissão no trajeto do axônio e ao longo da fibra muscular possui um jitter combinado menor do que 4μs ("jitter miogênico") . Na fibra muscular, a velocidade de propagação varia levemente em impulsos consecutivos, e depende do intervalo de descarga do impulso precedente (IDI -interdischarge interval ou intervalo entre descarga) (Stålberg, 1966 (Trontelj et al, 1986). Se a medida do jitter for realizada em frequências irregulares de descargas, a VRF contribuirá significativamente para o aumento do valor do jitter.…”

“…Adicionalmente, quando o IPI é maior do que 4ms, o efeito da VRF também é significativo (Trontelj et al, 1986 O jitter está mais comumente aumentado em distúrbios da JNM como:…”