Identification Procedure in a model of single fibre action potential – Part I: Estimation of fibre diameter and radial distance

Differentiation between single fiber potentials from one muscle fiber or contaminated by other fibers using discriminating function

OBJECTIVES

The aim was to improve the identification of potentials recorded using single fiber electromyography (SFEMG) contaminated by potentials from other muscle fibers, which might affect measured jitter value, by defining more selective criteria of single fiber potential (SFP) discrimination. We were looking for solutions suitable for automatization.

METHODS

Standard parameters characterizing SFP and their combinations were analyzed to define an analytical discriminating function able to verify if potentials recorded using SFEMG are due to single fiber or due to two (or more) fibers.

RESULTS

The discriminating function is based on combination of standard SFP parameters. The procedure was tested on a set of simulated i.e., known data and on samples of clinical data. The tests on simulated data confirmed assumed properties of discriminating function. Preliminary results of pilot studies using patient data suggest its ability for differentiation between potentials of one fiber and contaminated ones. The procedure is suitable for automatization.

CONCLUSION

Results suggest that proposed discriminating function when supplementing standard criteria would help to promote SFP recordings and enable to improve relevancy of jitter measurements and of jitter value norms.

Motor unit potentials with satellites in dystrophinopathies

INTRODUCTION

The objective of this study was to analyze the motor unit potentials (MUPs) with satellite components i.e., delayed by at least 2ms baseline from the main component, in the dystrophinopathies.

METHODS

The parameters of the MUPs recorded from the biceps brachii muscle in the Duchenne and Becker Muscle Dystrophy (DMD, BMD) were analyzed. The origin of the MUP satellite components was studied using a computer simulation.

RESULTS

As compared with normal potentials, both the main and the satellite MUP components are smaller in size, while the main components are more irregular. The computer simulation allows the range of muscle fiber diameters to be determined, and suggests that the variability characterizing diameters within the motor unit is responsible for generating the delayed, satellite components, via the linear relationship between the fiber diameter and the conduction velocity of the action potential.

DISCUSSION

The enhanced understanding of the origin of the MUP satellite components augments the knowledge about the relationship between muscle morphology and bioelectrical activity. The indirect evaluation of the range of muscle fiber diameters by means of a computer simulation may provide a new quantitative morphological data available from the EMG.

A method for determination of muscle fiber diameter using single fiber potential (SFP) analysis

We have used computer simulation to study the relationship between the muscle fiber diameter and parameters: peak-to-peak amplitude and duration of the negative peak of the muscle fiber action potential. We found that the negative peak duration is useful in the determination of fiber diameter via the diameter dependence of conduction velocity. We have shown a direct link between the underlying physiology and the measurements characterizing single fiber potential. Using data from simulations, a graphical tool and an analytical method to estimate the muscle fiber diameter from the recorded action potential has been developed. The ability to quantify the fiber diameter can add significantly to the single fiber electromyography examination. It may help study of muscle fiber diameter variability and thus compliment the muscle biopsy studies.

Analysis of the relationship between the rise-time and the amplitude of single-fibre potentials in human muscles

Using the core-conductor theory, a single fibre action potential (SFAP) can be expressed as the convolution of a biolectrical source and a weight function. In the Dimitrov-Dimitrova (D-D) SFAP convolutional model, the first temporal derivative of the intracellular action potential (IAP) is used as the source. The present work evaluates the relationship between the SFAP peak-to-peak amplitude (V(pp)) and peak-to-peak interval (rise-time, RT) at different fibre-to-electrode distances using simulated signals obtained by the D-D model as well as real recordings. With a single fibre electrode, we recorded 63 sets of consecutive SFAPs from the m. tibialis anterior of four normal subjects. The needle was intentionally moved whilst recording each SFAP set. We used the observed changes in RT and V(pp) within each SFAP set as a point of reference with which to evaluate how closely the relationship between RT and V(pp) provided by the D-D model reflects real data. We found that half of the recorded SFAP sets had rise-times higher than those generated by the D-D model. We also showed the influence of the IAP spatial length on the sensitivity of RT and V(pp) with radial distance. The study reveals some inaccuracies in simulated SFAPs whose origin might be related to the assumptions made in the core-conductor theory.