The influence of changes in hand temperature on the indirectly evoked electromyogram of the first dorsal interosseous muscle

The evoked EMG response commonly decreases in amplitude during the first few minutes of anaesthesia. The purpose of this study was to determine if a relationship exists between changes in hand temperature, which are known to occur with induction of anaesthesia, and drift in the EMG signal. The indirectly evoked response of the 1st dorsal interosseous muscle was measured using a Datex Relaxograph in 15 patients undergoing elective surgery. The test arm was wrapped in towels in order to minimize heat loss. Core body temperature, hand temperature, and T1 were recorded at two minute intervals for the next 30 min. Patients then received a bolus of mivacurium 0.08 mg.kg-1 and additional doses were given as needed. Complete recovery was defined as a TOF ratio > 0.90. Regression analysis plotting delta temperature against delta T1 was performed for each individual. The slope of the regression line for the relationship between delta degree C and delta T1 was then used to calculate a correction factor (CF) which might be used to "fine tune" the last measured T1. The initial hand temperature averaged 30.8 +/- 1.4 degrees C and this increased by 4.1 +/- 1.2 degrees C over the next 30 min. During this period T1 decreased by 24.8 +/- 5.9% or -6.05%/degrees C. The final mean T1 value at the end of anaesthesia (uncorrected) was 70.6 +/- 7% of control. The average corrected T1 value was 94.7 +/- 8.5% (range, 83-111%). It is concluded that there was a correlation between delta degree C and delta T1 during the first 30 min of anaesthesia (r2 = 0.77, P < 0.0001). However, in 5 of 15 individuals it was not possible to "temperature correct" the final T1 value to within +/- 10% of control. Hence, while changes in muscle temperature probably play a major role in the T1 drift seen with the Datex monitor, other factors remain to be identified.     

Handedness and asymmetry of hand representation in human motor cortex

The cortical representation of five simple hand and finger movements in the human motor cortex was determined in left- and right-handed people with whole-head magnetoencephalography. Different movements were found to be represented by spatially segregated dipolar sources in primary motor cortex. The spatial arrangement of neuronal sources for digit and wrist movements was nonsomatotopic and varied greatly between subjects. As an estimator of hand area size in primary motor cortex, we determined the smallest cuboid volume enclosing the five dipole sources within the left and right hemisphere of each subject. Interhemispheric comparison revealed a significant increase of this volume in primary motor cortex opposite to the preferred hand. This asymmetry was due to a greater spatial segregation of neuronal dipole generators subserving different hand and finger actions in the dominant hemisphere. Mean Euclidean distances between dipole sources for different movements were 10.7 +/- 3.5 mm in the dominant and 9.4 +/- 3.5 mm in the nondominant hemisphere (mean +/- SD; P = 0. 01, two-tailed t-test). The expansion of hand representation in primary motor cortex could not simply be attributed to a greater number of pyramidal cells devoted to each particular movement as inferred from current source amplitudes. The degree of hemispheric asymmetry of hand area size in the primary motor cortex was correlated highly with the asymmetry of hand performance in a standardized handedness test (r = -0.76, P < 0.01). These results demonstrate for the first time a biological correlate of handedness in human motor cortex. The expansion of hand motor cortex in the dominant hemisphere may provide extra space for the cortical encoding of a greater motor skill repertoire of the preferred hand.     

Summation of extraocular motor unit tensions in the lateral rectus muscle of the cat

Contractile measures on 67 single muscle units in the cat lateral rectus muscle were made in response to motoneuron stimulation. Simultaneous activation of four to five additional units, using muscle nerve stimulation, allowed an examination of unit force summation. Linear force addition was found in 73% of the units, while 25% added only about half of their twitch force to the twitch force of the nerve-activated units. "Nonadditive" units had significantly weaker twitch tensions than the units which added linearly. Lengthening or shortening the whole muscle, from maximal isometric settings, reduced whole muscle twitch tension as well as muscle unit tension. Injury to the lateral rectus muscle did not significantly alter whole muscle tension. These findings suggest that the known serial and branching arrangement of these muscle fibers, as well as the complex interfiber matrix, may help explain the force reduction in some muscle units and the whole muscle's resistance to insult.     

Fast-to-slow conversion following chronic low-frequency activation of medial gastrocnemius muscle in cats. I. Muscle and motor unit properties

This study of cat medial gastrocnemius (MG) muscle and motor unit (MU) properties tests the hypothesis that the normal ranges of MU contractile force, endurance, and speed are directly associated with the amount of neuromuscular activity normally experienced by each MU. We synchronously activated all MUs in the MG muscle with the same activity (20 Hz in a 50% duty cycle) and asked whether conversion of whole muscle contractile properties is associated with loss of the normal heterogeneity in MU properties. Chronically implanted cuff electrodes on the nerve to MG muscle were used for 24-h/day stimulation and for monitoring progressive changes in contractile force, endurance, and speed by periodic recording of maximal isometric twitch and tetanic contractions under halothane anesthesia. Chronic low-frequency stimulation slowed muscle contractions and made them weaker, and increased muscle endurance. The most rapid and least variable response to stimulation was a decline in force output of the muscle and constituent MUs. Fatigue resistance increased more slowly, whereas the increase in time to peak force varied most widely between animals and occurred with a longer time course than either force or endurance. Changes in contractile force, endurance, and speed of the whole MG muscle accurately reflected changes in the properties of the constituent MUs both in extent and time course. Normally there is a 100-fold range in tetanic force and a 10-fold range in fatigue indexes and twitch time to peak force. After chronic stimulation, the range in these properties was significantly reduced and, even in MU samples from single animals, the range was shown to correspond with the slow (type S) MUs of the normal MG. In no case was the range reduced to less than the type S range. The same results were obtained when the same chronic stimulation pattern of 20 Hz/50% duty cycle was imposed on paralyzed muscles after hemisection and unilateral deafferentation. The findings that the properties of MUs still varied within the normal range of type S MUs and were still heterogeneous despite a decline in the variance in any one property indicate that the neuromuscular activity can account only in part for the wide range of muscle properties. It is concluded that the normal range of properties within MU types reflects an intrinsic regulation of properties in the multinucleated muscle fibers.     

The utility of isokinetic dynamometry in the assessment of human muscle function

Isokinetic dynamometry has become a favoured method for the assessment of dynamic muscle function in both clinical research and sports environments. Several indices, such as peak torque, are used in the literature to characterise individual, group or larger population performance via these sophisticated data acquisition systems. Research suggests that there are several competing demands on the design of the measurement protocol which may affect the measurement of isokinetic strength and subsequent suitability of data for meaningful evaluation and interpretation. There is a need to increase measurement rigour, reliability and sensitivity to a level which is commensurate with the intended application, via more elaborate multiple-trial protocols. However, this may be confounded by logistical and financial constraints or reduced individual compliance. The net effect of the interaction of such demands may be considered to be the utility of the isokinetic dynamometry protocol. Of the factors which impinge on utility, those which relate to reliability afford the most control by the test administrator. Research data suggest that in many measurement applications, the reliability and sensitivity associated with all frequently-used indices of isokinetic leg strength which are estimated via single-trial protocols, are not sufficient to differentiate either performance change within the same individual or between individuals within a homogeneous group. While such limitation may be addressed by the use of protocols based on 3 to 4 inter-day trials for the index of peak torque, other indices which demonstrate reduced reliability, for example the composite index of the ratio of knee flexion to extension peak torque, may require many more replicates to achieve the same level of sensitivity. Here, the measurement utility of the index may not be sufficient to justify its proper deployment.     

Effects of a specific ecutaneous cold stimulus on single motor unit activity of medial gastrocnemium muscle in man

Fragmentation reactions of the biologically important N6-(3-methyl-2-butenyl)adenyl moiety have been re-examined with the aid of systematic deuterium labeling in the sidechain and by examination of the 1- and 7-deazanucleoside analogs. It is concluded that the diagnostic reactions which involve expulsion of C3H7 proceed predominantly by ring closure from the sidechain double bond to N-1 (ion a). Base-containing ions m/e 135 and 148 were confirmed to arise mainly by rearrangement of hydrogen from the methyl terminus to N6 and simple cleavage, respectively, but with significant contribution from other pathways involving transfer of sidechain hydrogens to the base.     

The motor unit potential distribution over the skin surface and its use in estimating the motor unit location

Dextransucrase (DSRS) from Leuconostoc mesenteroides NRRL B-512F is a glucosyltransferase that catalyzes the synthesis of soluble dextran from sucrose or oligosaccharides when acceptor molecules, like maltose, are present. The L. mesenteroides NRRL B-512F dextransucrase-encoding gene (dsrS) was amplified by the polymerase chain reaction and cloned in an overexpression plasmid. The characteristics of DSRS were found to be similar to the characteristics of the extracellular dextransucrase produced by L. mesenteroides NRRL B-512F. The enzyme also exhibited a high homology with other glucosyltransferases. In order to identify critical amino acid residues, the DSRS sequence was aligned with glucosyltransferase sequences and four amino acid residues were selected for site-directed mutagenesis experiments: aspartic acid 511, aspartic acid 513, aspartic acid 551 and histidine 661. Asp-511, Asp-513 and Asp-551 were independently replaced with asparagine and His-661 with arginine. Mutation at Asp-511 and Asp-551 completely suppressed dextran and oligosaccharide synthesis activities, showing that at least two carboxyl groups (Asp-511 and Asp-551) are essential for the catalysis process. However, glucan-binding properties were retained, showing that DSRS has a two-domain structure like other glucosyltransferases. Mutations at Asp-513 and His-661 resulted in greatly reduced dextransucrase activity. According to amino acid sequence alignments of glucosyltransferases, alpha-amylases or cyclodextrin glucanotransferases, His-661 may have a hydrogen-bonding function.     

The neurochemical coding and projections of circular muscle motor neurons in the human colon

BACKGROUND & AIMS: Enteric neurons can be characterized by their chemical coding, projections, and morphology. The aim of this study was to describe the different classes of human colonic circular muscle motor neurons. METHODS: Human colonic circular muscle motor neurons were identified by retrograde tracing with 1,1'-didodecyl 3,3,3',3'-indocarbocyanine perchlorate (Dil) applied to the circular muscle layer. Whole-mount preparations of the myenteric plexus were then double-labeled with antisera to choline acetyltransferase (ChAT) and/or nitric oxide synthase (NOS), or NOS and vasoactive intestinal peptide (VIP), and the position and immunoreactivity of Dil-filled neurons were recorded. RESULTS: Fifty-two percent of all Dil-filled neurons were ChAT immunoreactive, and 86% of these projected up to 11 mm orally, with 14% projecting short distances anally. Forty-eight percent of the Dil-filled neurons were NOS immunoreactive, and 77% of these projected up to 19 mm anally, with 23% projecting no more than 6 mm orally. A subpopulation of these NOS-immunoreactive motor neurons were also VIP-immunoreactive. A small population of myenteric neurons was immunoreactive for both ChAT and NOS, but none projected to the circular muscle. NOS-immunoreactive motor neurons projected for longer distances than those with ChAT immunoreactivity and were larger. CONCLUSIONS: There are two classes of human colonic motor neurons: one is excitatory (ChAT-immunoreactive) and mainly projects orally and the other is inhibitory (NOS +/- VIP immunoreactive) and projects preferentially anally.     

Extraocular motor unit and whole-muscle responses in the lateral rectus muscle of the squirrel monkey

Because primate studies provide data for the current experimental models of the human oculomotor system, we investigated the relationship of lateral rectus muscle motoneuron firing to muscle unit contractile characteristics in the squirrel monkey. Also examined was the correlation of whole-muscle contractile force with the degree of evoked eye displacement. A force transducer was used to record lateral rectus whole-muscle or muscle unit contraction in response to abducens whole-nerve stimulation or stimulation of single abducens motoneurons or axons. Horizontal eye displacement was recorded using a magnetic search coil. (1) Motor units could be categorized based on contraction speed (fusion frequency) and fatigue. (2) The kt value (change in motoneuronal firing necessary to increase motor unit force by 1.0 mg) of the units correlated with maximum tetanic tension. (3) There was some tendency for maximum tetanic tension of this unit population to separate into three groups. (4) At a constant frequency of 100 Hz, 95% of the motor units demonstrated significantly different force levels dependent on immediately previous stimulation history (hysteresis). (5) A mean force change of 0.32 gm/ degrees and a mean frequency change of 4.7 Hz/ degrees of eye displacement were observed in response to whole-nerve stimulation. These quantitative data provide the first contractile measures of primate extraocular motor units. Models of eye movement dynamics may need to consider the nonlinear transformations observed between stimulation rate and muscle tension as well as the probability that as few as two to three motor units can deviate the eye 1 degrees.     

Coordinated activation of muscle fibres by different conduction velocities in branches of a crustacean motor axon

Higher conduction velocities in branches of the fast excitor axon to distal muscle fibres ensure that these fibres are activated almost simultaneously with proximal fibres in the claw closer muscle of lobsters, producing a contraction of maximal force.     

The influence of age on the canine immune system

Immune function was assessed in a group of 47 Labrador Retrievers, ranging in age from 0.8 to 11.5 years, in order to establish baseline data on canine immunosenescence. Natural killer cell activity, lymphocyte subset distributions, antibody production, and mitogen-induced lymphoproliferative responses, all of which have been demonstrated to undergo age-related changes in humans and mice, were chosen as indicators of immune function. Dogs were categorized by age as young (mean 2.4 years), middle-aged (mean 5.8 years), and old (mean 9.1 years). Natural killer cell activity was not affected significantly by age. Lymphocyte subset analysis revealed a significant age-related increase in the percentage of cells staining with a pan T-cell reagent, accompanied by a corresponding increase in the percentage of CD8 cells from youth to middle age. An age-related decrease in the percentage of B-cells was observed concomitant with the increases in T-cell percentages. A gender-related difference in pan T-cell distribution was also observed, with females having a higher percentage than males. Lymphoproliferative responses of both young and middle-aged dogs to the mitogens concanavalin A, phytohemagglutinin, pokeweed mitogen, and staphylococcal enterotoxin B were significantly higher than those of old dogs. In general, the mitogen responses of male dogs were affected more dramatically by age than those of females. A significant age-related decline in in vivo antibody responses to the protein antigen, keyhole limpet hemocyanin, was not observed, although the mean titers of the young dogs were higher than those of the old.     

Somatotopy in the human motor cortex hand area. A high-resolution functional MRI study

Fine-scale somatotopic encoding in brain areas devoted to sensorimotor processing has recently been questioned by functional neuroimaging studies which suggested its absence within the hand area of the human primary motor cortex. We re-examined this issue by addressing somatotopy both in terms of functional segregation and of cortical response preference using oxygenation-sensitive magnetic resonance imaging at high spatial resolution. In a first step, spatial representations of self-paced isolated finger movements were mapped by using motor rest as a control state. A subsequent experimental design studied the predominance of individual finger movements by using contrasting finger movements as the control task. While the first approach confirmed previous reports of extensive overlap in spatial representations, the second approach revealed foci of differential activation which displayed an orderly mediolateral progression in accordance with the classical cortical motor homunculus. We conclude that somatotopy within the hand area of the primary motor cortex does not present as qualitative functional segregation but as quantitative predominance of certain movement or digit representation embedded in an overall joint hand area.     

Distinct patterns of motor unit behavior during muscle spasms in spinal cord injured subjects

Surface electromyograms (EMG) and force were recorded during repeated involuntary spasms of paralyzed triceps surae muscles of four men with chronic cervical spinal cord injury. The firing rates of 78 medial gastrocnemius (MG) motor units also were recorded intramuscularly with tungsten microelectrodes. Spasms typically involved a relatively rapid rise, then a more gradual fall in triceps surae EMG and torque. Motor unit firing rates either increased and then decreased with the spasm intensity (54%) or were relatively constant (26%), firing mainly at 2-10 Hz. The remaining units (20%) produced trains that included one or several doublets. Mean peak spasm firing rates were 18 +/- 9 Hz (mean +/- SD) for rate modulated units and 11 +/- 10 Hz for units with little or no rate modulation. Some motor units fired at rates comparable with those recorded previously during maximum voluntary contractions performed by intact subjects. Others fired at rates below the minimum usually seen when normal units are first recruited (< 6 Hz). Doublets (interspike interval < 10 ms) often repeated every 123-333 ms, or were interspersed in trains firing at low steady rates (< 11 Hz). This study shows that rate coding for many motor units appears to be similar whether descending motor input is intact or whether it has been reduced severely by spinal cord injury. In contrast, rate modulation in other units appears to depend mainly on voluntary motor commands.     

Lateral rectus whole muscle and motor unit contractile measures with the extraocular muscles intact

Both extracellular and intracellular stimulation of single motoneurons were shown to be similarly effective and consistent in eliciting contractile responses in single lateral rectus muscle motor units. The whole muscle was activated by stimulating the sixth nerve in the brain stem. Both whole muscle and motor unit contractile characteristics, under isometric conditions, were found to remain consistent regardless of whether this extraocular muscle was detached or left attached to the globe. In addition, whole muscle twitch and maximum tetanic tension evoked by sixth nerve stimulation was significantly less than would be predicted by the linear summation of individual motor unit twitch and maximum tetanic tensions.     

The influence of patient age on the effectiveness of bronchodilators

The beta adrenergic receptors are exposed to variety of factors modulating their activity. We analyzed the sensitivity to Salbutamol in asthmatic patients divided into three group (I-30 yr; II-30-50 yr; III-50 yr). The effectiveness of beta adrenergic receptors was assessed by means of estimation of plasma cAMP level before and after Salbutamol infusion. We didn't found any significant differences in plasma cAMP changes between investigated group of patients.     

Does walking speed influence the time pattern of muscle activation in normal children?

Dynamic electromyography (EMG) of the extrinsic muscles of the ankle is used more and more frequently to assist in the planning of tendon transfers in children with equinovarus deformities. Since these children walk at low speeds (1 to 4km/h), and since walking speed modifies the EMG-time pattern, the clinical investigator must be able to differentiate EMG modifications due to pathology versus those due to slow walking speed. The aim of this work was to study the effect of walking speed on the EMG-time pattern of the extrinsic ankle muscles in healthy children between 4 and 11 years of age. This pattern was found to change significantly with speed of progression but is independent of growth over this age range. A nomograph of EMG timing, taking into account walking speed, is proposed for clinical gait analysis.