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PubMed1995

Movement-related cortical potentials associated with voluntary muscle relaxation.

We recorded movement-related cortical potentials (MRCPs) associated with voluntary muscle relaxation, which was not accompanied by contraction of the antagonist or any other muscles, in 10 normal subjects. Voluntary, self-paced relaxation of the wrist extensors from the extended position was employed as the relaxation task, and wrist flexion by muscle contraction was employed as the contraction task. The accelerogram was used to obtain the trigger signals for both tasks. The electromyograms of the ipsilateral agonist and antagonist, the proximal muscles and the contralateral corresponding muscles were monitored to confirm the absence of muscle contraction for the relaxation task. All MRCP components were identified in both tasks; Bereitschaftspotential (BP), negative slope (NS'), parietal peak of motor potential (ppMP) and frontal peak of motor potential (fpMP). BP started earlier and was larger at the contralateral parietotemporal electrodes for the relaxation than for the contraction task, and the slow positive shift at the bilateral frontopolar electrodes was seen more often in the relaxation task. It is concluded that the voluntary muscle relaxation needs a cortical preparatory process similar to voluntary muscle contraction, and needs a more extensive and longer preparation process in the primary motor area and possibly in other motor areas as compared with the contraction.

Adult↗
PubMed1982

Does the sarcoplasmic reticulum achieve chemiosmotic equilibrium in relaxed muscle?

Measurements of 45Ca2+ efflux from bovine skeletal muscle fibres preloaded with this isotope indicate that the sarcoplasmic free Ca2+ concentration rises and falls under anaerobic (or uncoupled) and aerobic conditions, respectively. Dantrolene has only a small effect on these responses which are larger in predominantly slow-twitch fibre preparations. Dantrolene slightly reduces the resting free Ca2+; this is much more pronounced in rectus abdominis (mainly fast-twitch) than in sternomandibularis (mainly slow-twitch). It is proposed that the sarcoplasmic reticulum in the resting muscle fibre achieves a state close to chemiosmotic equilibrium and that aerobic metabolism generates a higher phosphorylation potential, permitting a larger Ca2+ electrochemical potential difference to develop across the sarcoplasmic reticulum membrane under aerobic conditions.

2,4-Dinitrophenol↗
PubMed1997

Motor unit discharge rate is not associated with muscle relaxation time in sustained submaximal contractions in humans.

The muscle wisdom hypothesis suggests that motor unit discharge rates decrease in parallel with the slowing of muscle contractile properties during fatigue. In this study, the discharge rates of single motor units and the muscle contractile properties were measured during a sustained submaximal contraction. The majority of motor units that were active from the beginning of the task demonstrated a decline in discharge rate in the absence of any slowing of muscle relaxation time. These findings suggest that the muscle wisdom hypothesis may not apply to sustained submaximal contractions.

Adult↗
PubMed2004

[Effect of progressive muscle relaxation using biofeedback on perceived stress, stress response, immune response and climacteric symptoms of middle-aged women].

PURPOSE: This study was aimed to evaluate the effect of progressive muscle relaxation training using biofeedback on perceived stress, stress response, immune response and climacteric symptoms. METHOD: This was a crossover, pre-post test design. The study subjects are 36 middle-aged women who were selected at 2 public health centers. The independent variable was Biofeedback training for 4 weeks, twice a week and home training for 4 weeks. Dependent variables were perceived stress, stress response, immune response, and climacteric symptoms measured with Hildtch's scale (1996). RESULT: Progressive muscle relaxation training using biofeedback was not effective in reducing perceived stress, but it was shown to be effective in reducing physiological stress responses such as pulse rate and EMG. Though blood pressure and skin conductance were repeatedly down, and skin temperature slowly increased, there were no statistically significant differences. Progressive muscle relaxation training using biofeedback was not effective in reducing serum cortisol, enhancing immune responses, or decreasing climacteric symptoms. CONCLUSION: The findings point to a pressing need for further, well-controlled and designed research with consideration in selection of subjects and instruments, frequency of measurements, the sampling method, and intervention modalities.

Adult↗
PubMed1988

Train-of-four fade of non depolarizing muscle relaxants: an insight into the mechanism of precurarization.

This study was carried out to assess the prejunctional effect of non depolarizing muscle relaxants during the onset of neuromuscular blockade using the train-of-four ratio (TR). The prejunctional effect was compared with previous results concerning the ability of the relaxants to prevent suxamethonium-induced fasciculations. Fifty-three adult patients were relaxed with small incremental doses of either alcuronium (0.03 mg.kg-1), atracurium (0.04 mg.kg-1), pancuronium (0.01 mg.kg-1), d-tubocurarine (0.05 mg.kg-1) or vecuronium (0.01 mg.kg-1) during anaesthesia with thiopentone, fentanyl and nitrous oxide in oxygen. The muscle relaxant was given after recovery from an initial suxamethonium blockade needed for tracheal intubation. The evoked integrated EMG response to supramaximal train-of-four (2 Hz) stimulation was recorded every 20 s. TR % was calculated at different first twitch (T1) levels during the onset of neuromuscular blockade. Significant changes occurred at the 100% and 90% T1 levels, alcuronium having the lowest mean TR values. Atracurium, pancuronium and vecuronium gave similar TR values. Results with d-tubocurarine placed it between alcuronium and the others. These train-of-four ratio results were compared with the ability of non depolarizing muscle relaxants to prevent fasciculations. In conclusion, the stronger the train-of-four fade, the greater was the ability of the relaxant to prevent suxamethonium-induced fasciculations. This supports the theory that the blockade of prejunctional cholinergic receptors is the mechanism of action of precurarization.

Adolescent↗
PubMed1975

A paradoxical action of minute doses of nondepolarizing muscle relaxants in anaesthetized man.

The administration of minute doses of all currently available nondepolarizing muscle relaxants result in an increase in contractile force of the skeletal muscles. This surprising finding has been obtained by means of mechanograms of the hand muscles after electrical stimulation of the ulnar nerve (100-200 volts, 0.3 msec, 0.2 Hz). Higher doses produce a decrease in contractile force and a paralysis of the skiltalmuscles. The paradoxical action of muscle relaxants can be explained by repetitive firing of the muscle action potential as has been demonstrated in the phrenic nerve-diaphragm preparation with tubocurarine and gallamine.

Action Potentials↗
PubMed1989

Presynaptic effect of muscle relaxants on the release of 3H-norepinephrine controlled by endogenous acetylcholine in guinea pig atrium.

The influence of nondepolarizing muscle relaxants (MR) on the resting and electrically evoked release of tritiated norepinephrine (3H-NE) was investigated, in the absence and presence of 10(-4) mol/l cocaine, in the in vitro right atrium preparation of guinea pigs (g.p.) preloaded with 3H-NE. In the absence of MR both resting and stimulated 3H and 3H-NE release remained relatively constant throughout the experiment and the ratios of the evoked release of 3H during consecutive stimulation periods (i.e. S2/S1, S3/S2) were close to unity. None of the MR had any effect on resting 3H release. Atropine (3 x 10(-7) mol/l), gallamine (7 x 10(-5) mol/l), and pancuronium (2 x 10(-6) mol/l), but not d-tubocurarine (5 x 10(-6) mol/l) significantly increased stimulated release of 3H-NE. The effect of MR on resting or evoked release of 3H-NE was not influenced by 10(-4) mol/l cocaine. In the presence of atropine gallamine and pancuronium did not affect the release of 3H-NE. This finding indicates that the effect of MR was mediated via presynaptic muscarinic receptors. Muscle relaxants and atropine inhibited these receptors and removed the tonic inhibitory effect of acetylcholine (ACh) released from the parasympathetic nerve endings on the release of NE from the sympathetic nerve. This was substantiated by the finding that in the present of cholinesterase inhibition, when the effect of endogenous ACh was amplified and thereby the cholinergic tone was dominant, the total release of 3H-NE evoked by stimulation was much lower and muscle relaxants and atropine were much more effective to enhance 3H-NE release. Gallamine and pancuronium also increased the force of contraction of the electrically stimulated atria. These findings indicate that the acceleration of the heart rate observed with gallamine and pancuronium in anesthetized man is due to increased release from, and not the inhibition of reuptake of NE by the sympathetic nerve endings of the right atrium.

Acetylcholine↗
PubMed1991

Effect of short-term muscle relaxation on neonatal plasma volume.

OBJECTIVES: To study the effect of pancuronium-induced muscle relaxation on circulating plasma volume. DESIGN: A prospective, controlled study. Consecutive infants who were paralyzed with pancuronium and a comparative group who were not paralyzed during mechanical ventilation were studied. SETTING: Neonatal ICU of a regional referral university-affiliated hospital. PATIENTS: Newborn infants weighing greater than 1700 g who required respiratory assistance within 24 hrs of birth and who were free of congenital heart disease, sepsis, or blood loss were eligible for entry into the study. Infants who received colloid infusions during the study period were excluded. A total of 17 consecutive infants (nine paralyzed and eight nonparalyzed control infants) were studied. Four paralyzed infants and one nonparalyzed infant received colloid infusions before the completion of the study and were excluded from the final analysis. MEASUREMENTS: Plasma volume was measured three times in the paralyzed infants: a) immediately before the first dose of pancuronium, b) after 12 to 24 hrs, and c) greater than or equal to 12 hrs after the return of muscle activity, but before extubation. Plasma volume in the nonparalyzed, control infants was measured at the time of intubation, 12 to 24 hrs after commencing mechanical ventilation, and 12 hrs after extubation. Plasma volume was measured using the Evans blue dye dilution technique. RESULTS: There were no changes in the plasma volume or blood volume in the three measurements among both the paralyzed and nonparalyzed infants. CONCLUSION: Pancuronium-induced muscle relaxation in mechanically ventilated newborn infants weighing greater than 1700 g did not alter circulating plasma volume in 24 hrs.

Evans Blue↗
PubMed2003

Reduction of blood pressure response during strength training through intermittent muscle relaxations.

UNLABELLED: The increase in blood pressure during training is a disadvantage of strength training in the elderly. To reduce this effect it is generally recommended to apply lower levels of relative muscle strength with longer contraction durations or higher number of repetitions (continuous mode (CM), e. g. 50% of maximal strength, 10 to 15 repetitions without pauses). Alternatively, higher contraction forces could be combined with frequent periods of muscle relaxation and fewer repetitions (intermittent mode (IM), e. g. 80% of maximal strength, 8 repetitions consisting of 1.5 s concentric contraction, 1.5 s eccentric contraction and 3 s pause). We compared the blood pressure effects of both approaches during leg press exercise in two age groups (10 subjects aged 22 to 42 y, 9 subjects aged 60 to 72 y). Blood pressure was measured continuously by a non-invasive method (FINAPRES, Ohmeda 2300, Englewood USA). RESULTS: 1. The age of the subjects had no significant influence on the slopes of blood pressure increase during the different exercise modes. 2. The frequent insertion of short (3 s) periods of muscle relaxation (IM) decreased the blood pressure response more effectively than a reduction in contraction strength alone (CM). Short muscle relaxations have an immediate, mechanical effect on blood pressure and they allow a metabolic recovery which attenuates the trend of blood pressure increase.

Adult↗
PubMed1991

Hemodynamic effects of muscle relaxant drugs during anesthetic induction in patients with mitral or aortic valvular heart disease.

The hemodynamic effects of three nondepolarizing skeletal muscle relaxant drug regimens were compared during the induction of general anesthesia in 64 patients with valvular heart disease using a double-blind protocol. Patients were first stratified according to primary valvular defect (aortic stenosis, aortic regurgitation, mitral stenosis, or mitral regurgitation). Next, patients were randomly allocated to a drug group, either group A (atracurium), group V (vecuronium), or group MP (metocurine plus pancuronium). Data were collected during three periods: awake, postanesthetic induction, and posttracheal intubation. Four cardiovascular variables were designated a priori as primary variables of interest. These were heart rate (HR), mean arterial pressure (MAP), cardiac index (CI), and systemic vascular resistance index (SVRI). Patients with mitral stenosis showed two significant hemodynamic differences among muscle relaxant drug groups: (1) CI increased in group A but decreased in group MP between the awake and postinduction measurements (P = 0.032); and (2) SVRI decreased in group A but increased in group MP between the awake and postintubation periods (P = 0.034). In contrast, patients with aortic stenosis, aortic regurgitation, or mitral regurgitation demonstrated no statistically significant difference in cardiovascular responses among drug groups. Further analysis was performed using the following data: (1) other hemodynamic variables; (2) incidence of deviations from cardiovascular stability; and (3) the frequency of cardiovascular drug use. This examination showed no important differences among the muscle relaxant drug groups. The small but significant hemodynamic changes observed in mitral stenosis patients in drug groups A and MP were not noted with vecuronium.(ABSTRACT TRUNCATED AT 250 WORDS)

Anesthesia, Intravenous↗
PubMed1990

The degree of muscle relaxation requested by the surgens during upper abdominal surgery.

The degree of muscle relaxation required for the abdominal surgery should differ at different phase of operation. To test this hypothesis muscle relaxation was assessed subjectively by the surgeon and the results were compared with quantitative observations of the degree of response depression to train of four (t4) stimulation at various stages of surgery. Maximum relaxation, with a t4 ratio of less than 10%, was required immediately after the skin incision and during closure of the abdominal wall, while the requirement was minimal during the major part of surgery when the intra-abdominal procedures were performed.

Journal Article↗
PubMed1985

Evaluation of the muscle relaxant properties of a novel beta-carboline, ZK 93423 in rats and cats.

The muscle relaxant action of ZK 93423 (6-benzyloxy-4-methoxymethyl-beta-carboline-3-carboxylate ethyl ester), a novel beta-carboline with agonistic properties at the benzodiazepine receptor, was examined by assessing its effect on the tonic electromyogram (EMG) activity of the gastrocnemiussoleus (GS) muscle of genetically spastic rats and on ventral root reflexes, presynaptic inhibition and fusimotor activity in the spinal cord of decerebrate cats. ZK 93423 (0.1-10.0 mg kg-1) depressed the tonic EMG activity in mutant rats in a dose-dependent manner. This effect was reversed by the benzodiazepine antagonist Ro 15-1788 (5.0 mg kg-1). Both ZK 93423 (0.5 mg kg-1) and diazepam (0.3 mg kg-1) enhanced the presynaptic inhibition of the GS muscle and associated dorsal root potentials in decerebrate cats in an almost identical manner. The actions of both drugs were reversed by Ro 15-1788 (5.0 mg kg-1). ZK 93423 (0.5 mg kg-1) and diazepam (0.3 mg kg-1) depressed the activity of both static and dynamic fusimotor neurones, as deduced from changes in the afferent responses of muscle spindle primary endings to low frequency (1 s-1) sinusoidal stretching. The depressant action of diazepam (0.3 mg kg-1) was weaker than that of ZK 93423 (0.5 mg kg-1). The actions of both drugs were reversed by Ro 15-1788 (5.0 mg kg-1). ZK 93423 (0.5 mg kg-1) failed to alter the magnitude of monosynaptic ventral root reflexes evoked by electrical stimulation of a flexor and an extensor nerve, whereas diazepam (0.3 mg kg-1) had a depressant effect on both types of monosynaptic reflexes, which was antagonized by Ro 15-1788 (5.0 mg kg-1). Neither ZK 93423 (0.5 mg kg-1) nor diazepam (0.3 mg kg-1) depressed polysynaptic ventral root reflexes evoked by electrical stimulation of a flexor and a cutaneous nerve. The present results demonstrate that ZK 93423 exerts a potent muscle relaxant action due to a specific interaction with benzodiazepine receptors. However, its profile of actions on spinal motor mechanisms is not identical to that of diazepam.

Animals↗