M-wave Amplitude Research Articles

Central basis of muscle fatigue in chronic fatigue syndrome

We studied whether muscle fatigue, metabolism, or activation are abnormal in the chronic fatigue syndrome (CFS). Subjects performed both an intermittent submaximal and a sustained maximal voluntary isometric exercise protocol of the tibialis anterior muscle. The extent of fatigue, metabolic response, and changes in both M-wave amplitude and twitch tension during exercise were similar in patients and controls. The response to systemic exercise was also normal in the patients. However, voluntary activation of the tibialis was significantly lower in the patients during maximal sustained exercise. The results indicate that patients with CFS have (1) normal fatigability and metabolism at both the intracellular and systemic levels, (2) normal muscle membrane function and excitation-contraction coupling, and (3) an inability to fully activate skeletal muscle during intense, sustained exercise. This failure of activation was well in excess of that found in controls, suggesting an important central component of muscle fatigue in CFS.

ZPT-related distal axonopathy: Behavioral and electrophysiologic correlates in rats

These experiments examined the relationship between behavioral and electrophysiologic signs of neuromuscular dysfunction in rats with zinc pyridinethione (ZPT)-induced neurotoxicity. ZPT added to the diet of adult rats at 50 ppm produced a moderate (approximately 200 g) reduction in forelimb and hindlimb grip strength which occurred during the second week of dosing. Other behavioral tests of peripheral nervous system toxicity were affected inconsistently. Electrophysiologic changes included a marked (maximum 95%) reduction of indirect muscle-evoked potential (M-wave) and a decrement (maximum 30%) during repetitive M-wave elicitation. Electrophysiologic changes were greater in hindlimb than in forelimb. Needle electromyography revealed denervation potentials in ZPT-treated rats which appeared after M-wave changes and recovered faster than did M-wave amplitude. Caudal nerve conduction velocity was unaffected, indicating that peripheral neurotoxic effects were confined to the neuromuscular junction. When ZPT exposure was discontinued, grip strength recovered in about 1 week. In contrast, electrophysiologic measures required 42 days to recover completely. These results indicate that deficits in neuromuscular junction physiology are a sensitive index of ZPT-related distal axonopathy.

Electromyogram and force during stimulated fatigue tests of muscles in dominant and non-dominant hands

Mechanical and electrical properties were studied for the first dorsal interosseous muscle of the dominant (d-FDI) and non-dominant hand (nd-FDI). Observations were made before, during and after a fatigue test, fatigue being evoked by percutaneous electrical stimulation of the ulnar nerve. The test consisted of 30 Hz bursts of ten supramaximal 0.1 ms pulses, repeated once a second for 5 min. The measurements included the amplitude of the first and fifth compound muscle action potentials (M-waves) within bursts, the peak burst force and the amplitude and time course of single twitches. At the end of the fatigue test, burst force had decreased to about the same extent in the FDI of both hands. The final decline in first M-wave amplitude was, however, significantly more pronounced for the nd-FDI than for the d-FDI. There were no longer any significant discrepancies between the two muscles after a subsequent recovery-period of 15 min. Comparisons among nd-FDI of various individuals demonstrated the presence of significant inter-individual differences in fatigue-related force-drop without any associated differences in M-wave decline. Intra-individual variability was similar for fatigue-related force-drop and M-wave decline.

Failure of neuromuscular propagation during human maximal voluntary contraction.

The mechanism for fatigue of the adductor pollicis was studied in normal subjects during maximal voluntary contractions (MVC) sustained for 90-100 s, by comparing the force and electrical response of this muscle to voluntary motor drive with that obtainable with artificial stimulation of the ulnar nerve. The adequacy of nerve stimulation was checked by recording simultaneously the electrical response of a nonfatiguing muscle, the abductor of the small finger. The decrease in force and in the natural electrical activity with fatigue was accompanied by a parallel decrease in the amplitude of synchronous muscle action potentials (M waves) evoked by artificial stimulation of the ulnar nerve at different frequencies. The decline in M-wave amplitude in the adductor pollicis was not due to a submaximal nerve stimulation, since the amplitudes recorded simultaneously from the nonfatiguing abductor digiti minimi remained unchanged. The force and the electrical responses from the adductor pollicis recovered in parallel with a half time of approximately 1 min. These results suggest that the loss of force of the adductor pollicis with fatigue and its subsequent recovery are largely determined by the extent of neuromuscular propagation failure. The slow recovery of the M-wave amplitude during repetitive stimulation suggests that it may be related to some aspect of muscle metabolism.

PROBLEMS IN THE MOTOR NERVE CONDUCTION STUDY

Motor nerve conduction studies of the median and ulnar nerves were carried out in twenty healthy normal subjects by conventional techniques. The amplitude of motor action potential (M-wave) and the distal motor latency time were measured by stimulating at the wrist. The amplitude from negative to positive peak was considered to the M-wave response. The time from stimulus artifact to the first deflection was taken as the distal motor latency time.The pick-up electrode was firstly placed on the middle portion of the muscle belly and the conduction study was performed, then the pick-up electrode was placed 1cm distally and same study was carried out. Thus, the amplitude and latency time were compared according to the different site of pick-up electrodes.The results were shown in the following table:In 1cm distal part of muscle belly, the amplitude of M-wave was approximately 70% of that of the middle portion in both median and ulnar innervated muscles. But distal motor latency times at the two different portions were statistically unchanged.It is concluded that the distal motor latency time is more valuable indicator in motor nerve conduction study. Also if the pick-up electrode was placed precisely over the middle of muscle belly tested, the amplitude of M-wave is reproducible, then it will become good indicator in motor nerve conduction study.

A cortical evoked potential that reflects the conditioned, positive incentive value of the stimulus. III. Manipulative motivation and the value of the reward

Changing animals from a schedule on which they had to bar-press after a tone cue to get a food pellet, to a schedule on which the food pellet was presented automatically after the tone cue and the manipulandum was not available, had no effect on the latency, amplitude, or shape of the M-wave evoked by the tone cue. The amplitude of the evoked wave did, however, decrease more rapidly, as a test session progressed, with the latter schedule than with the former schedule. Failure to fast animals before test sessions markedly reduced the amplitude of the M-wave. Variation in the type of food pellet used caused marked variations in the amplitude of the evoked response. In all cases, there was a high degree of correlation between M-wave amplitude and a behavioral indication of the animal's interest in the reward. It was concluded that the M-wave reflects the conditioned incentive value of the cue, or, in other words, the level of interest of the animal in the reward.

EFFECTS OF ACUTE HYPOCAPNIA AND HYPERCAPNIA ON NEUROMUSCULAR TRANSMISSION AND ON MONOSYNAPTIC SPINAL REFLEX IN WAKEFUL MAN

SUMMARY The effects of both acute hypocapnia and hypercapnia on neuromuscular transmission (NMT) and monosynaptic spinal reflex (MSR) in conscious subjects were studied by observing the averaged evoked electromyogram. The M-wave amplitude increased to 165 ± 25% (mean ± standard error) during acute hypocapnia with an end expiratory carbon dioxide concentration of 2.5 ± 0.2 vol.% and decreased to 73 + 7% during acute hypercapnia with an expiratory concentration of 6.8 ±0.1 vol.%, in comparison with the control value. The H-wave amplitude increased to 226 ±82% during acute hypocapnia and decreased to 85 ± 9% during acute hypercapnia in comparison with the control value. These results indicate that both NMT and MSR in conscious man are facilitated by acute hypocapnia, and that NMT is inhibited by acute hypercapnia. However, the effect of acute hypercapnia on MSR could not be ascertained only by the observation of the H reflex in these conditions.

An analysis of evoked electromyogram from orbicularis oculi in patients with myasthenia gravis.

Summary Evoked electromyograms of the orbicularis oculi muscle with repeated stimulation given at frequencies of 5, 10, 20, 50 and 100 c/s were examined in myasthenia gravis; and the following results were obtained. 1. In the normal subject, the amplitude of M-waves showed almost no change by stimulation at frequencies of 5 and 10 c/s, and a mild gradual increase by stimulation at a frequency of 20 c/s. On stimulation with 50 and 100 c/s, the amplitude of M-waves showed a marked gradual increase and maintained nearly the peak value after a maximum had been reached. 2. In a total of 23 patients with myasthenia gravis, the amplitude of M-waves showed several specific changes against the stimulation frequencies employed. The patterns of the amplitude of M-waves appearing with each frequency were classified into 3 types: Type I, which showed an initial gradual decrease in amplitude with all the stimulation frequencies employed, was observed in 13 patients (56.5%). Type II, which showed an initial gradual decrease at frequencies of 5 c/s and 10 c/s, but a gradual increase followed by gradual decrease at frequencies of 50 and 100 c/s, was observed in 8 patients (34.8%). Type III, which showed no obvious difference from the pattern of the normal curve with stimulation given at not more than 50 c/s but a gradual increase followed by gradual decrease at a frequency of 100c/s, was observed in 2 patients (8.7%). 3. No distinct differences were noted in other neuromuscular diseases taken as control, as compared with the normal.

Effect of neostigmine, d-tubocurarine and clinical condition on evoked electromyogram from orbicularis oculi in myasthenia gravis.

Summary In our previous report, evoked electromyograms of the orbicularis oculi muscle with repetitive stimulation given at frequencies of 5, 10, 20, 50 and 100 c/s were examined in myasthenia gravis. The amplitude of M-waves showed several specific changes against the stimulation frequencies employed. The patterns of the amplitude of M-waves appearing with each frequency could be classified into 3 types, Type I, Type II and Type III according to relation between the frequency of stimulation and decrease and/ or increase of M-wave amplitude. In the present study, the effect of neostigmine, d-tubocurarine and clinical condition on the various pattern of M-wave amplitude curve classified into above mentioned three types was examined.