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Biomedical subjects

M Mihelin

Publications and source records attributed to M Mihelin.

11 recordsLinked to original sources
PubMed1992

Jitter of the stimulated motor axon.

Electrical microstimulation of motor axons in conjunction with single fiber EMG (SFEMG) is increasingly used to measure the jitter of the motor endplates. This study examines the jitter of the stimulation site on the axon when stimulus strength is at threshold. In the absence of spurious blocking, this was found to be 5 microseconds on the average. With intermittent blocking, however, a mean additional jitter of 40 microseconds was obtained. The latter is considered to result from changing propagation velocity in the muscle fiber due to irregularity of activation rate. In clinical jitter studies, inadvertent threshold stimulation can result in significant error when associated with intermittent blocking.

Adult↗
PubMed1992

Electrical microstimulation with single-fiber electromyography: a useful method to study the physiology of the motor unit.

This article reviews the essential technical principles and findings with electrical microstimulation as used in conjunction with single-fiber electromyography (SFEMG). It highlights the details in the microphysiology of the motor unit that can be conveniently studied with these methods, particularly the neuromuscular transmission at the individual motor endplates, muscle fiber recovery functions, and a variety of late responses. The differences, advantages, and disadvantages of the stimulation method of jitter measurement, compared to the original method, in the voluntarily activated muscle are described. Special attention is given to the pitfalls of the technique. Indications for clinical use of stimulation SFEMG in the electromyography laboratory are suggested.

Axons↗
PubMed1991

Muscle fiber recovery functions studied with double pulse stimulation.

Direct electrical stimulation with paired pulses at varied intervals was used to study the propagation velocity and action potential amplitude recovery functions (VRF and ARF) of single muscle fibers. Following a subnormal period with slowed conduction, most of the muscle fibers tested in healthy subjects showed a period of supernormal propagation velocity starting at 3 to 12 ms, with a peak between about 5 and 15 ms, a mean increase of 7%, and an approximately logarithmic decay toward 1 second. The onset of supernormality was earlier in muscle fibers from patients with muscular dystrophy and significantly delayed in those from denervated muscles. Denervated muscle fibers also had a significantly longer refractory period.

Action Potentials↗
PubMed1990

Jitter in the muscle fibre.

Direct stimulation of muscle fibres with a regular 10 Hz rate, three computer generated random rhythms and a sequence of voluntary discharges was used to quantify the interdischarge interval (IDI) dependent jitter due to velocity recovery function (VRF). This jitter was found to depend on conduction time and strength of VRF, but not on propagation velocity. The results suggest that in the usual jitter study in voluntarily activated muscle fibre pairs, with moderately irregular discharge rate and interpotential intervals below 3 ms the IDI dependent jitter contributes on average less than 10 microseconds, but can be so large as to produce false abnormal values at more irregular rates, longer interpotential intervals and pronounced differences in VRF. It can be effectively removed by mathematical algorithms or, better still, by using electrical stimulation.

Adult↗
PubMed1988

The jitter in stimulated orbicularis oculi muscle: technique and normal values.

A technique is described of measuring the motor end plate jitter in the orbicularis oculi muscle activated by extra-muscular nerve stimulation, standardised for routine use in diagnosis and evaluation of neuromuscular transmission disorders. Among the advantages of the technique are comparatively quick and easy sampling of adequate number of single motor end-plates, convenient control of discharge rate between less than 1 and up to 20 Hz, absence of direct muscle fibre responses, and little discomfort for the patient. The jitter in the orbicularis oculi is significantly lower than that in the extensor digitorum communis muscle. There is a positive correlation between the jitter and the latency of the individual muscle fibre responses, possibly indicating that smaller diameter muscle fibres have slightly lower safety factor of neuromuscular transmission. The data collected in a group of healthy volunteers suggest the following upper normal limits for the mean of absolute consecutive difference of the latency: 30 microseconds for individual motor end plates (one out of 20 values may be higher), and 18 microseconds for a median of 20 motor end plates.

Adult↗
PubMed1988

Facioscapulohumeral dystrophy: jitter in facial muscles.

Motor end plate jitter was studied by single fibre EMG in the orbicularis oculi muscle of eight patients with facioscapulohumeral dystrophy activated by extramuscular nerve stimulation. The jitter was found to be slightly larger in comparison with the normal controls, although still within the normal limits in each patient. The findings are considered to indicate absence of any significant neuromuscular transmission disturbance, inflammatory or regenerative process, or reinnervation in progress. There was no evidence of muscle fibre conduction abnormality even in very weak muscle.

Adolescent↗
PubMed1987

Percutaneous stimulation of human corticospinal tract: a single-fibre EMG study of individual motor unit responses.

The technique of electrical stimulation of the brain through intact scalp was applied to activate the corticospinal tract (CST) of healthy human volunteers. Single motoneurone responses were picked up by a special (single fibre EMG) needle electrode. Our finding of relatively small latency variation of consecutive single motor unit responses seems to support the concept of predominantly monosynaptic transmission at the spinal level. The alternation between several discrete latencies seems to reflect a complexly shaped spinal motoneurone excitatory postsynaptic potential (EPSP), which could be due to either alternating direct/indirect (via other cerebral neurones) activation of the corticospinal tract (CST) neurones, or alternating mono- or oligosynaptic transmission at the spinal level, or multiple CST impulses in response to a single stimulus.

Adult↗
PubMed1986

Axonal stimulation for end-plate jitter studies.

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 interval-dependent jitter, as well as a possible failure to recognise split muscle fibres. The mean MCD on axonal stimulation was only 5.2 microseconds 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 microseconds, 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 microseconds (individual muscle fibres) and 25 microseconds (mean of 30 muscle fibres).

Adolescent↗
PubMed1979

Jittermeter--a microcomputer-based system for single fibre electromyography.

In single fibre electromyography (SFEMG) an exact measurement and computation of a number of time parameters is required. This paper describes a low-cost microprocessor-based measurement system for SFEMG data acquisition, computation of the parameters and display, as an alternative to a general purpose-computer based system. Time measurement is performed at dual resolution: 0.1 microsecond and 0.1 msec. Erroneous data due to disturbing voltages are automatically eliminated. A variety of SFEMG applications is covered by 3 basic modes of data handling. The microprocessor unit is based on the 6800 family and contains 3K of program memory, input-output modules and 4K data memory. The instructions are entered through a keyboard and output is provided by an LED display, line-printer and X-Y storage display.

Action Potentials↗
PubMed1975

Automatic measurement of random interpotenial intervals in single fibre electromyography.

The paper describes computer-aided measurement of interpotential intervals in single fibre eletromyography (SFEMG), a diagnostic and research method in clinical medicine. The method is based on analysis of consecutive intervals in pairs of single muscle fibre action potentials. The most important parameter obtained is the mean value of absolute differences of consecutive interpotential intervals, which reflects the reliability of impulse conduction along the terminal branches of motor axons and across the neuromuscular junction. The interface units, in combination with amplifers, binary counters and pulse amplitude-to-pulse width converters, allow not only direct analogue-to-digital conversion but also recognition of potentials. This enables the computer system to make decisions. The results are computed in less than 1 sec after analysis, and are immediately displayed in a graphic and alpha-numberical form on a screen at the measurement site. This provides an immediate visual feedback for the investigator thus both increasing the diagnostic efficacy and reducing the discomfort to the patient. Simultaneous printout by a teletype is used for documentation. The computer system consists of an HP 2116C computer with standard periphery and the program has been written in FORTRAN IV language with subroutines in FORTRAN IV and ASSEMBLER languages.

Action Potentials↗