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E Stålberg

Publications and source records attributed to E Stålberg.

At least 19 recordsLinked to original sources
PubMed1995

Can the size principle be detected in conventional EMG recordings?

According to Henneman's size principle, small motor units are recruited before large ones. It is commonly believed that this can be detected in routine conventional EMG recordings even among the earliest recruited motor units. That is, the MUP amplitude, area, and thickness should increase with recruitment order. We studied the first four motor unit potentials (MUPs) recruited within the pickup area of the electrodes. Data were obtained from 179 different sites in monopolar recordings and in 153 concentric recordings from 5 health subjects. In the pooled material, amplitude, area, and thickness increased slightly between consecutively recruited MUPs. However, at individual recording sites the size of consecutively recruited MUPs varied considerably. At some recording sites the first recruited MUP had the largest amplitude and the later MUPs has successively smaller amplitudes. We conclude that, at individual recording sites, the size principle cannot be detected in low threshold motor units with monopolar or concentric EMG electrodes. The reason for this is the small uptake area of these electrodes in relation to the motor unit territory.

Action Potentials↗
PubMed1995

Dynamic electromyography and muscle biopsy changes in a 4-year follow-up: study of patients with a history of polio.

Eighteen patients who had had polio 29-56 years prior to the first investigation were studied on two occasions, 4 years apart. Isokinetic and isometric strength measurements and Macro EMG were performed in 28 legs. Muscle biopsy specimens were obtained on both occasions from 11 legs. On average the muscle strength was 56% of control values at the first examination, and decreased by another 8% during the observation period. The muscle fiber area was increased compared to that of controls and did not change significantly. Macro EMG, comprising muscle fiber area and number of muscle fibers, and/or single fiber EMG showed clear signs of reinnervation in all legs. The motor units at the first examination were increased 11-fold, on average, compared with age-matched control values. During the observation period, reinnervation continued and the size of motor units increased by another 56% as a result of ongoing denervation, that is, loss of neurons. This compensation was particularly pronounced in patients with stable conditions. The parameters studied did not reveal any definite pattern predicting future development of new muscle weakness in individual subjects.

Adenosine Triphosphatases↗
PubMed1995

Influence of recording site within the muscle on motor unit potentials.

The influence of the recording site on the motor unit potentials (MUPs) was investigated in the brachial biceps muscle of 8 healthy subjects. The MUPs were recorded with a concentric needle electrode and analyzed with a new decomposition EMG program we call multi-MUP analysis. MUPs had shorter durations and smaller amplitudes at superficial recording sites than at deeper sites in the muscle. This is mainly due to the cannula of the concentric electrode, which records a higher potential at superficial recording sites and partially cancels the recorded potentials from the tip in a differential recording. The MUPs had longer durations and higher amplitudes distally than in the middle of the muscle. The longer durations and spike durations are probably due to increased temporal dispersion at a greater distance from the endplate zone. We do not have an adequate explanation for the larger amplitudes distally in the biceps, they may be due to anatomical factors. To increase the diagnostic sensitivity of quantitative MUP analysis the recordings should be obtained from standardized recording sites.

Adult↗
PubMed1995

Multi-MUP EMG analysis--a two year experience in daily clinical work.

A new quantitative motor unit potential (MUP) analysis method, called multi-MUP analysis, is described. Multi-MUP analysis is a type of decomposition analysis of the EMG signal. At each site 6 different MUPs may be recorded during an epoch of 4.8 sec. Calculation time is about 3 sec. A study of 20-30 MUPs including editing takes 4-8 min. Compared to many earlier MUP analysis methods it is faster and more user friendly, therefore it can be used in daily routine EMG analysis. The accuracy and reliability of the method are good. The differences from methods based on manual analysis, spike triggered averaging, template matching and decomposition are discussed. The main advantages of multi-MUP analysis are: (1) quick acquisition of many MUPs; (2) simultaneous collection of several MUPs at one recording site; (3) possibility to analyze not only low threshold MUPs; (4) less bias in the selection of MUPs; and (5) the reproducibility of the results that allow the same reference values to be used in different laboratories. So far we have successfully used this method for 2 years on more than 2000 patients.

Electromyography↗
PubMed1994

Outliers, a way to detect abnormality in quantitative EMG.

In visual analysis of motor unit potentials it is common to decide abnormality by a few motor unit potentials with definitely abnormal amplitude, duration, and shape. The aim of the present investigation was to define limits of normal values and to compare the diagnostic yield of assessing definitely abnormal values outliers, with conventional mean values of MUP parameters. MUPs were extracted and measured with a new decomposition method. Reference values were obtained for three commonly studied muscles. Patients with various types of neuropathies and myopathies were studied in the same way with measurement of outliers and mean values. It was found that outliers were as sensitive as mean values in neuropathies and better in myopathies. Often an increased number of outliers could already be detected after only a few MUPs had been obtained. It would not have been necessary to obtain all 20 MUPs in these patients. The conclusion is that the outlier method is as sensitive as mean values. Because the number of MUPs required may be reduced, the investigation takes a shorter time and is less painful for the patient. If the degree of abnormality is to be quantified, calculation of mean values is still necessary. The combination of outliers and mean values may be the optimal way to detect and express abnormality.

Electromyography↗
PubMed1994

Reference values of motor unit action potentials obtained with multi-MUAP analysis.

We collected reference values of motor unit action potentials (MUAPs) from healthy deltoid, brachial biceps, first dorsal interosseous, lateral vastus, and anterior tibial muscles in 105 subjects between 15 and 86 years. The MUAPs were recorded with a concentric needle electrode and extracted with a decomposition method we call multi-MUAP analysis. The main goal is to identify and extract MUAPs. Also, the firing pattern of the motor units can be followed. No significant changes with age were found for duration, spike duration, thickness, amplitude, area, size index, or number of phases in all muscles studied. We did not find any influence of gender or height. We found higher amplitudes and shorter durations compared with previous studies. This may be due to a higher contraction level that can be used with a decomposition technique. No right-left side differences were found. The coefficient of variation of the parameters in repeated examinations was small, which implies a good reliability of the measurements. Interexaminer variability of four investigators was not greater than in repeated studies.

Action Potentials↗
PubMed1994

Naloxone reduces alterations in evoked potentials and edema in trauma to the rat spinal cord.

The influence of naloxone (an opioid receptor antagonist) on spinal cord conduction and edema formation as a result of trauma to the cord was investigated in a rat model. The spinal cord injury (SCI) was inflicted in urethane anesthetized animals by a longitudinal incision into the right dorsal horn of the T10-11 segments, about 2 mm deep and 5 mm long. Spinal cord evoked potentials (SCEP) were recorded epidurally from the T9 (rostral) and T12 (caudal) segments after stimulation of the ipsilateral tibial and sural nerves at the ankle. The edema was measured by determining water content of the cord at s h after injury. In rats not given naloxone SCI resulted in an immediate long-lasting depression of the rostral maximal negative peak (MNP) amplitude (about 60%) and a significant increase in the latency of the rostral maximal positive peak (MPP). Pretreatment with naloxone inhibited the immediate post-injury decrease of the rostral MNP and some of the increase of MPP latency. The water content in the traumatized spinal cord was reduced by 3% in naloxone treated animals compared with untreated injured controls. Our results indicate that endogenous opioid peptides participate in changes of spinal cord conduction after trauma and influence edema formation probably via multiple opioid receptors.

Afferent Pathways↗
PubMed1994

New approaches to motor unit potential analysis.

The current state of motor unit potential (MUP) analysis is reviewed. New quantitative analysis methods are described and compared with traditional manual measurements. The emphasis in this review is on a new method, multi-MUP analysis and the detection of individual outliers. Multi-MUP analysis is based on decomposition EMG. The main advantage of these new methods is that they save time and allow immediate comparison between obtained results and reference values. The results are repeatable and independent of the investigator.

Animals↗
PubMed1994

Opioid receptors influence spinal cord electrical activity and edema formation following spinal cord injury: experimental observations using naloxone in the rat.

The possibility that opioid peptides participate in alteration of spinal cord conduction following trauma to the cord was investigated in a rat model using a pharmacological approach. Spinal cord injury was produced in urethane anesthetized animals by a longitudinal incision into the right dorsal horn of T10-11 segments (2 mm deep and 5 mm long). Spinal cord evoked potentials (SCEP) were recorded epidurally from the T9 (rostral) and T12 (caudal) segments after stimulation of the ipsilateral tibial and sural nerves at the ankle. SCEP from both rostral and caudal segments consisted of a small positive peak followed by a high negative peak. Infliction of trauma in untreated rats resulted in an immediate depression of the rostral maximal negative peak (MNP) amplitude. This depression was long-lasting. Later, a significant increase in the latency of the rostral MNP amplitude occurred. Naloxone was administered in a high dosage (10 mg/kg, i.p.) to block mu-, delta- and kappa-opioid receptors 30 min before injury. This drug treatment inhibited the immediate post-injury decrease of the rostral MNP amplitude without any significant effect on latency changes. Measurement of water content in the traumatized spinal cord segment showed a significant reduction in the drug treated animals 5 h after trauma (71.46 +/- 0.54) as compared with untreated controls (74.65 +/- 0.76). However, 1 mg or 5 mg/kg dosages of the drug were not effective in reducing the SCEP changes or edema after injury. These results strongly suggest that blockade of kappa-opioid receptors with high doses of naloxone is important in reduction of trauma induced alteration of SCEP and edema formation in spinal cord injury.

Animals↗
PubMed1993

Facial nerve enhancement in Bell's palsy demonstrated by different gadolinium-enhanced magnetic resonance imaging techniques.

Twenty-one patients with an acute complete peripheral facial palsy, Bell's palsy, were examined by medium- and high-Tesla magnetic resonance imaging. Three contrast techniques were used: intravenous gadolinium; oral carbohydrate and intravenous gadolinium; and gadolinium, carbohydrate, and readministration of gadolinium. Three to 22 days after the onset of palsy, 12 of the 21 patients demonstrated ipsilateral facial nerve enhancement, most consistently in the meatal region, which is indicative of an inflammatory reaction. Two to 4.5 months after the onset, the enhancement had disappeared in 10 of the 12 patients. For the individual patient, contrast-enhanced magnetic resonance imaging gave little or no help in predicting the outcome of palsy. It is speculated that the intake of carbohydrate and readministration of gadolinium may improve the sensitivity of medium-high-Tesla magnetic resonance imaging in some cases.

Administration, Oral↗
PubMed1993

The ability of MUP parameters to discriminate between normal and neurogenic MUPs in concentric EMG: analysis of the MUP "thickness" and the proposal of "size index".

The ability of a motor unit potential (MUP) parameter or a set of parameters to discriminate between control MUPs and MUPs from muscles with severe to moderate inactive neurogenic changes was investigated using discriminant analysis. As a single parameter, area gave rather good discrimination, while amplitude, duration and area/amplitude did not give good discrimination. Only 15-30% of MUPs from neurogenic muscles were judged to be abnormal by duration alone. The combination of amplitude and the area/amplitude ratio (area/amp; MUP thickness) improved the discrimination considerably and around 70% of MUPs in the neurogenic group were judged to be abnormal. A simple assigned discriminant function, 2 x log 10(amp) + area/amp, gave similar good results for both biceps brachii and tibialis anterior muscles, and this value was named as "size index." The experiment of manual scanning of an MUP revealed that area/amp increases, that is, the MUP becomes thicker, as the amplitude decreases for each MUP with increasing recording distance, while the size index remains almost constant for each MUP irrespective of the electrode position. The new parameter, size index, is promising since it is more stable and gives better discrimination results than duration.

Adult↗
PubMed1993

A pilot trial of dextromethorphan in amyotrophic lateral sclerosis.

Assuming the presence of glutamate-induced neurotoxicity in amyotrophic lateral sclerosis 14 patients were treated with dextromethorphan, an N-methyl-D-aspartate receptor antagonist. The patients were treated with 150 mg dextromethorphan or placebo daily for 12 weeks in a double-blind crossover trial, with a wash out period of 4 weeks between the two treatment periods. Thereafter the surviving patients were treated with 300 mg dextromethorphan daily for up to 6 months in an open trial. No positive effects on clinical or neurophysiological parameters (relative number of axons, and compound muscle action potentials in the abductor digiti minimi muscle) were observed either in the double-blind trial or in the open trial.

Aged↗
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↗