Diaphragm muscle weakness in an experimental porcine intensive care unit model

In critically ill patients, mechanisms underlying diaphragm muscle remodeling and resultant dysfunction contributing to weaning failure remain unclear. Ventilator-induced modifications as well as sepsis and administration of pharmacological agents such as corticosteroids and neuromuscular blocking agents may be involved. Thus, the objective of the present study was to examine how sepsis, systemic corticosteroid treatment (CS) and neuromuscular blocking agent administration (NMBA) aggravate ventilator-related diaphragm cell and molecular dysfunction in the intensive care unit. Piglets were exposed to different combinations of mechanical ventilation and sedation, endotoxin-induced sepsis, CS and NMBA for five days and compared with sham-operated control animals. On day 5, diaphragm muscle fibre structure (myosin heavy chain isoform proportion, cross-sectional area and contractile protein content) did not differ from controls in any of the mechanically ventilated animals. However, a decrease in single fibre maximal force normalized to cross-sectional area (specific force) was observed in all experimental piglets. Therefore, exposure to mechanical ventilation and sedation for five days has a key negative impact on diaphragm contractile function despite a preservation of muscle structure. Post-translational modifications of contractile proteins are forwarded as one probable underlying mechanism. Unexpectedly, sepsis, CS or NMBA have no significant additive effects, suggesting that mechanical ventilation and sedation are the triggering factors leading to diaphragm weakness in the intensive care unit.     

Acute nerve stretch and the compound motor action potential

In this paper, the acute changes in the compound motor action potential (CMAP) during mechanical stretch were studied in hamster sciatic nerve and compared to the changes that occur during compression.In response to stretch, the nerve physically broke when a mean force of 331 gm (3.3 N) was applied while the CMAP disappeared at an average stretch force of 73 gm (0.73 N). There were 5 primary measures of the CMAP used to describe the changes during the experiment: the normalized peak to peak amplitude, the normalized area under the curve (AUC), the normalized duration, the normalized velocity and the normalized velocity corrected for the additional path length the impulses travel when the nerve is stretched. Each of these measures was shown to contain information not available in the others.During stretch, the earliest change is a reduction in conduction velocity followed at higher stretch forces by declines in the amplitude of the CMAP. This is associated with the appearance of spontaneous EMG activity. With stretch forces < 40 gm (0.40 N), there is evidence of increased excitability since the corrected velocities increase above baseline values. In addition, there is a remarkable increase in the peak to peak amplitude of the CMAP after recovery from stretch < 40 gm, often to 20% above baseline.Multiple means of predicting when a change in the CMAP suggests a significant stretch are discussed and it is clear that a multifactorial approach using both velocity and amplitude parameters is important. In the case of pure compression, it is only the amplitude of the CMAP that is critical in predicting which changes in the CMAP are associated with significant compression.     

Electrophysiological Motor Unit Number Estimation (MUNE) Measuring Compound Muscle Action Potential (CMAP) in Mouse Hindlimb Muscles

Compound muscle action potential (CMAP) and motor unit number estimation (MUNE) are electrophysiological techniques that can be used to monitor the functional status of a motor unit pool in vivo. These measures can provide insight into the normal development and degeneration of the neuromuscular system. These measures have clear translational potential because they are routinely applied in diagnostic and clinical human studies. We present electrophysiological techniques similar to those employed in humans to allow recordings of mouse sciatic nerve function. The CMAP response represents the electrophysiological output from a muscle or group of muscles following supramaximal stimulation of a peripheral nerve. MUNE is an electrophysiological technique that is based on modifications of the CMAP response. MUNE is a calculated value that represents the estimated number of motor neurons or axons (motor control input) supplying the muscle or group of muscles being tested. We present methods for recording CMAP responses from the proximal leg muscles using surface recording electrodes following the stimulation of the sciatic nerve in mice. An incremental MUNE technique is described using submaximal stimuli to determine the average single motor unit potential (SMUP) size. MUNE is calculated by dividing the CMAP amplitude (peak-to-peak) by the SMUP amplitude (peak-to-peak). These electrophysiological techniques allow repeated measures in both neonatal and adult mice in such a manner that facilitates rapid analysis and data collection while reducing the number of animals required for experimental testing. Furthermore, these measures are similar to those recorded in human studies allowing more direct comparisons.     

神经传导测定技术对腕管综合征病情评估的价值

目的:近年来腕管综合征发病率逐年升高,然而其慢性、隐匿性不易引起人们的重视,发现时往往已造成较大的危害。本文探讨腕管综合征的神经传导测定对病情评估的临床价值,旨在为患者腕管综合征早期发现和后续治疗提供进一步的临床参考依据。方法:选取我院124例确诊的腕管综合征患者。其中无大鱼际肌萎缩者有64例,并选取平均年龄相近的64例正常人作为对照(组A);有大鱼际肌畏缩者60例,并选取平均年龄相近的60例正常人作为对照(组B)。A、B组均经行神经电图检查,握力测定和两点辨别觉测定,分析神经传导速度改变与感觉、运动功能减退程度的关系。结果:A、B两组患者均有不同程度的神经传导改变:在A组患者神经传导改变中,运动和感觉传导速度(MCV和SCV)轻度下降,运动和感觉电位波幅(CMAP和SNAP)轻度下降,潜伏期(ML)轻度延长;在B组患者神经传导中,运动和感觉传导速度(MCV和SCV)明显下降,运动和感觉电位波幅(CMAP和SNAP)明显下降,潜伏期明显延长。结论:腕管综合征患者不同的临床表现有不同程度的神经电图表现,因此神经电图对神经传导的测定结果对腕管综合征患者的病情有良好的评估价值,值得临床推广。     

Axillary artery injury combined with delayed brachial plexus palsy due to compressive hematoma in a young patient: a case report

Aim

To prove the possibility of axillary nerve conduction changes following shoulder subluxation due to hemiplegia, in order to investigate the usefulness of screening nerve conduction studies in patients with hemiplegia for finding peripheral neuropathy.

Methods

Forty-four shoulders of twenty-two patients with a first-time stroke having flaccid hemiplegia were tested, 43 ± 12 days after stroke onset. Wasting and weakness of the deltoid were present in the involved side. Motor nerve conduction latency and compound muscle action potential (CMAP) amplitude were measured along the axillary nerve, comparing the paralyzed to the sound shoulder. The stimulation was done at the Erb's point whilst the recording needle electrode was inserted into the deltoid muscle 4 cm directly beneath the lateral border of the acromion. Wilcoxon signed rank test was used to compare the motor conduction between the sound and the paralytic shoulder. Mann-Whitney test was used to compare between plegic and sound shoulder in each side.

Results

Mean motor nerve conduction latency time to the deltoid muscle was 8.49, SD 4.36 ms in the paralyzed shoulder and 5.17, SD 1.35 ms in the sound shoulder (p < 0.001). Mean compound muscle action potential (CMAP) amplitude was 2.83, SD 2.50 mV in the paralyzed shoulder and was 7.44, SD 5.47 mV in the sound shoulder (p < 0.001). Patients with right paralyzed shoulder compared to patients with right sound shoulder (p < 0.001, 1-sided for latency; p = 0.003, 1-sided for amplitude), and patients with left paralyzed shoulder compared to patients with left sound shoulder (p = 0.011, 1-sided for latency, p = 0.001, 1-sided for amplitude), support the same outcomes. The electro-physiological changes in the axillary nerve may appear during the first six weeks after stroke breakout.

Conclusion

Continuous traction of the axillary nerve, as in hypotonic shoulder, may affect the electro-physiological properties of the nerve. It most probably results from subluxation of the head of the humerus, causing demyelinization and even axonopathy. Slowing of the conduction velocities of the axillary nerve in the paralyzed shoulders may be related also to the lowering of the skin temperature and muscular atrophy in the same limb. The usefulness of routine screening nerve conduction studies in the shoulder of hemiplegic patients seems to be advocated.     

Influence of 50 Hz-1 mT magnetic field on human median nerve

In this study, human median nerve was exposed to power frequency magnetic fields in order to provide clarification for possibly changeable nerve conduction mechanism. The nerve was exposed to 50 Hz magnetic field by utilizing a special Helmholtz applicator. The experiments were carried out with six healthy human-volunteers. Median motor distal amplitude/proximal amplitude ratios were recorded from adult human median nerve pre-exposure, during, and post-exposure to a 50 Hz, 1 mT magnetic field. The result of 18 measurements shows that median motor distal amplitude/proximal amplitude ratio significantly decreases in pre-exposure state as compare to post exposure of which. The results of this study may be useful for some nerve rehabilitation, excitation, and stimulation in more effective/safe physical therapy. Additionally, 50 Hz, 1 mT sinusoidal magnetic field should not be recognizing as safe for conduction mechanism on a nerve. These mechanisms would be cleared by new advanced engineering models in other future works.     

肌电图检查评估腕管综合征手术效果的临床分析

目的:探讨采用肌电图检查评估腕管综合征的手术治疗效果。方法:选取35例(患侧手共39侧)临床确诊为腕管综合征并接受腕管切开减压术治疗的患者,于手术前后分别行肌电图检查,应用正中神经传导检查和拇短展肌针极肌电图检查,分析患者手术前和手术后腕部正中神经功能的变化情况。结果:手术后,患者正中神经感觉传导潜伏期异常率(33%)、正中神经运动传导潜伏期异常率(36%)较手术前(72%、74%)明显下降(P0.05),正中神经感觉传导波幅(7.40±5.05)较手术前(4.86±3.60)显著降低(P0.001),拇短展肌静息状态下失神经电位的异常率(69%)、重收缩时募集电位异常率(13%)均较手术前(85%、26%)明显下降(P0.05)。患者手术前后正中神经感觉传导速度和运动传导速度对比差异无统计学意义(P0.05)。结论:腕管切开减压术可解除正中神经卡压状态,明显恢复正中神经功能,增强拇短展肌肌力,临床治疗效果好。肌电图检查可为腕管综合征患者手术治疗效果的评估提供客观的依据。     

Physiologic changes of compound muscle action potentials related to voluntary contraction and muscle length in carpal tunnel syndrome.

The affect of muscle length and voluntary contraction upon compound muscle action potentials (CMAPs) in subjects with carpal tunnel syndrome (CTS) has been evaluated. Twenty-five hands in a CTS patient group and 29 hands in a normal subject control group were studied. The CMAPs from the abductor pollicis brevis induced by median nerve stimulation at the wrist were obtained for five thumb positions: neutral, abduction for shortening with and without contraction, and adduction for lengthening with and without contraction. Upon muscle shortening with relaxation, CMAP duration decreased in both groups, whereas waveform amplitude increased in the control group and showed no significant change in the CTS group. Muscle shortening with contraction afforded decreased CMAP duration and increased CMAP amplitude in both groups. Upon muscle lengthening with relaxation, both groups showed a reduction in CMAP amplitude and an increase in CMAP duration. Upon lengthening with contraction, CMAP duration decreased in the control group; in contrast, the CTS group showed further amplitude reduction and the waveform duration returned to the neutral value. These results demonstrate that, in patients with CTS, physiologic CMAP summations by muscle shortening or contraction may be less effective, whereas decreases in amplitude and increases in duration may be accentuated by lengthening and contraction.     

Staircase potentiation in isolated frog skeletal muscle: power spectral analysis of the evoked compound muscle action potential

1. The mechanical and electrophysiological effects of repetitive, low-frequency electrical stimulation on paired sartorii muscles from small male frogs have been investigated, in vitro. 2. Stimulation for 90 sec at 5 Hz resulted in a progressive rise (staircase) than fall (fatigue) in peak twitch tension. 3. The root mean square amplitude, peak-to-peak amplitude, conduction velocity and mean power frequency of evoked compound muscle action potentials (CMAPs) decreased over the stimulation period. 4. Results suggest that alterations in the shape of the CMAP during repetitive stimulation may contribute to the staircase phenomenon.     

Primary Hyperparathyroidism is Associated With subclinical Peripheral Neural Alterations

ObjectiveSome case reports have suggested primary hyperparathyroidism (PHPT) and peripheral polyneuropathy (PPN) are associated; however, there are no reports of studies examining this possible relationship. The aim of this study was to evaluate peripheral nerve conduction in subjects with PHPT.MethodsThe study involved 17 patients with PHPT. Mean patient age was 60.5 ± 12.9 years, serum calcium concentration was 11.5 ± 1.0 mg/dL, and the serum parathyroid hormone (PTH) level was 315 ± 569 pg/dL. The control group comprised 17 individuals without PHPT. The mean age of controls was 60.8 ± 12.5 years and the serum calcium concentration was 9.8 ± 0.3 mg/dL. Motor and sensory nerve conduction was assessed by electroneurography (ENG).ResultsThe following ENG parameters differed significantly between the PHPT and control groups: right (R) sural sensory nerve action potential conduction velocity (52.7 ± 6.3 m/s versus 58.0 ± 8.0 m/s; P = .041); R median compound muscle action potential (CMAP) amplitude (7.4 ± 1.6 mV versus 8.9 ± 1.7 mV; P = .002); R median CMAP latency (4.3 ± 1.2 ms versus 3.6 ± 0.6 ms; P = .032); R tibial CMAP latency (4.2 ± 1.1 ms versus 3.3 ± 0.4 ms; P = .001). The neurological examination was normal in all patients.ConclusionOur data demonstrate an association between PHPT and peripheral neurological alterations, consistent with subclinical sensory-motor PPN. (Endocr Pract. 2013;19:219-225)     

Neuronal adaptation of corticospinal mechanisms of muscle contraction regulation in athletes

Adaptation changes in the corticospinal mechanisms of muscle contraction control in athletes were investigated. Using the transcranial magnetic stimulation method, the parameters of motor evoked potentials of skeletal muscles of the lower limbs during voluntary static loads of various intensities and durations were measured. Athletes, as compared to the reference group, exhibited a greater increase in the maximal amplitude of the motor evoked potentials of the skeletal muscles of the lower limbs, a smaller decrease in the central motor conduction time of nerve pulses and the peripheral period in electromyograms, and a smaller increase in the cortical and segmental silent periods with increasing intensity and duration of isometric muscle contractions. The mechanisms of adaptation of corticospinal regulation of human muscle contraction to specific conditions of extreme motor activities are discussed.     

Myoelectric signal conduction velocity and spectral parameters: influence of force and time

Reports on measurement of muscle fiber conduction velocity in humans are scarce. Inferences on the behavior of conduction velocity have been drawn from the behavior of myoelectric spectral parameters. The present report contains information on conduction velocity and spectral parameters studied at various muscle contraction levels and during and after sustained contractions. The following results have been obtained from measurements on the tibialis anterior muscle. Conduction velocity demonstrated a positive correlation with limb circumference and with muscle force output. Thus we conclude that the diameters of the muscle fibers of high-threshold motor units are, on an average, larger than those of low-threshold motor units. The study of a sustained contraction and on the recovery after such a contraction revealed that conduction velocity consistently decreased during a strong contraction as did various myoelectric spectral parameters. However, the spectral parameters decreased approximately twice as much as did the conduction velocity, and we conclude that factors other than the conduction velocity along the muscle fibers affect the myoelectric signal during a high-level contraction. These other factors appertain to changes in the firing statistics of individual motor units as well as the correlation between the firings of different motor units.     

Conduction velocity of low-threshold motor units during ischemic contractions performed with surface EMG feedback.

The aim of this study was to analyze the effect of ischemia on low-threshold motor unit conduction velocity. Nine subjects were trained to isolate the activity of a single motor unit (target motor unit) in the abductor pollicis brevis muscle with feedback on surface EMG signals recorded with a 16-electrode linear array. After training, the subjects activated the target motor unit at approximately 8 pulses per second (pps) for five 3-min-long contractions. During the third and fourth contractions, a cuff inflated at 180 mmHg around the forearm induced ischemia of the hand. The exerted force (mean +/- SE, 4.6 +/- 2.1% of the maximal voluntary contraction force), discharge rate (8.6 +/- 0.4 pps), interpulse interval variability (34.8 +/- 2.5%), and peak-to-peak amplitude of the target motor unit action potentials (176.6 +/- 18.2 microV) were not different among the five contractions. Conduction velocity, mean power spectral frequency, and action potential duration were the same in the beginning of the five contractions (2.8 +/- 0.2 m/s, 195.2 +/- 10.5 Hz, and 5.4 +/- 0.3 ms, respectively) and changed over the 3 min of sustained activation only during the fourth contraction. Conduction velocity and mean power spectral frequency decreased (10.05 +/- 1.8% and 8.50 +/- 2.18% during the 3 min, respectively) and action potential duration increased (8.2 +/- 4.6% in the 3 min) during the fourth contraction. In conclusion, 1) subjects were able to isolate the activity of a single motor unit with surface EMG visual feedback in ischemic conditions maintained for 16 min, and 2) the activation-induced decrease in single motor unit conduction velocity was significantly larger with ischemia than with normal circulation, probably due to the alteration of mechanisms of ion exchange across the fiber membrane.     

Force and surface mechanomyogram relationship in cat gastrocnemius.

The aim of this study was to compare the force (F) and the muscle transverse diameter changes during electrical stimulation of the motor nerve. In four cats the exposed motor nerves of the medial gastrocnemius were stimulated as follows: (a) eight separate trials at fixed firing rates (FR) from 5 to 50 Hz (9 s duration, supramaximal amplitude); (b) 5 to 50 Hz linear sweep in 2.5, 5, 7.5 and 10 s (supramaximal amplitude, separate trials); (c) four separate trials at 40 Hz, the motor units (MUs) being orderly recruited in 2.5, 5, 7.5 and 10 s. The muscle surface displacement was detected by a laser distance sensor pointed at the muscle surface. The resulting electrical signal was termed surface mechanomyogram (MMG). In stimulation patterns (a) and (b) the average F and MMG increased with FR. With respect to their values at 50 Hz the amplitude of the unfused signal oscillations at 5 Hz was much larger in MMG than in force. The signal rising phase was always earlier in MMG than in F. In (c) trials, F increased less in the first than in the second half of the recruiting time. MMG had an opposite behaviour. The results indicate that the force and the lateral displacement are not linearly related. The different behaviour of F and MMG, from low to high level of the MUs' pool activation, suggests that the force generation and the muscle dimensional change processes are influenced by different components of the muscle mechanical model.     

Electrophysiological and histopathological changes in peripheral nerves of postnatally undernourished and rehabilitated young rhesus monkeys

Nerve condition velocity of ulnar and tibial nerves and qualitative histology of ulnar nerve were studied in young rhesus monkeys. Motor nerve condition velocity of both the nerves and amplitude of sensory response of ulnar nerve were significantly decreased in even moderate protein calorie malnourished (PCM) group of monkeys. Increased paranodal gap, segmental demyelination, thin myelinated fibres and prominent Schmidt Lanterman Clefts were also observed in PCM group. There was complete recovery in motor nerve conduction velocity in the nerves of both limbs while partial in amplitude of sensory response in proximal segment of ulnar nerve on nutritional rehabilitation of 10-12 weeks.     

Forced-exercise attenuates experimental autoimmune neuritis

Physical inactivity in combination with a sedentary lifestyle is strongly associated with an increased risk of development of inflammatory-mediated diseases, including autoimmune disorders. Recent studies suggest that anti-inflammatory effects of physical exercise may be of therapeutic value in some affected individuals. In this study, we determined the effects of forced-exercise (treadmill running) on the development and progression of experimental autoimmune neuritis (EAN), an established animal model of Guillain-Barré syndrome. Adult male Lewis rats were subjected to sedentary (control) or forced-exercise (1.2 km per day, 5 days a week) for three weeks prior to induction of EAN. P2 (53-78)-immunized sedentary control rats developed a monophasic course of EAN beginning on post-injection day 12.33 ± 0.59 (n = 18) and reaching peak severity on day 15.83 ± 0.35 (n = 18). At near peak of disease, ankle- and sciatic notch-evoked compound muscle action potential (CMAP) amplitudes in sedentary control rats were reduced (~50%) while motor nerve conduction velocity (MNCV) was slowed (~30%) compared with pre-induction evoked responses. In marked contrast, rats undergoing forced-exercise exhibited a significantly less severe clinical course of EAN beginning on post-injection day 12.63 ± 0.53 (n = 16) and reaching peaking severity on day 14.69 ± 0.73 (n = 16). At near peak of disease, ankle- and sciatic-notch-evoked CMAP amplitudes in forced-exercised rats were preserved while EAN-associated slowing of MNCV was modestly attenuated by exercise. Three weeks of forced-exercise reduced by 46% total plasma corticosterone content while elevating the levels of corticosteroid binding globulin. We conclude from this study that forced-exercise administered prior to and during development of EAN affords a novel measure of protection against autoimmune-associated deficits in peripheral nerve evoked responses independent of steroid-induced immune suppression.     

Electromyographic Characteristics of Muscle Fatigue in Parkinsonian Patients Exposed to General Heating

Surface electromyography and turn–amplitude analysis were used to study muscle fatigue after exposure to heating (40°C, 60 min) and under thermoneutral conditions (22°C) in 12 parkinsonian patients from 57 to 65 years of age treated with Nacom, Bromocryptin, and Cyclodol. In the patients, heating caused a twofold increase in the motor performance (number of contractions until exhaustion and nerve conduction velocity) and a decrease in the mean electromyogram (EMG) amplitude and number of turns of spontaneous muscle activity. The spontaneous EMG activity was fully inhibited after exposure to heating and fatigue, suggesting a thermoregulatory dependence of the spontaneous muscle tone (rigidity) in parkinsonian patients. After exposure to heating, fatigue also caused a decrease in the peak ratio with a shift of the mean EMG amplitude to lower values. After-load recovery of the mean EMG amplitude was slower under heating versus thermoneutral conditions and was compensated for by an increased number of turns.     

Optimal stimulation settings for CMAP scan registrations

Background

The CMAP (Compound Muscle Action Potential) scan is a non-invasive electrodiagnostic tool, which provides a quick and visual assessment of motor unit potentials as electrophysiological components that together constitute the CMAP. The CMAP scan records the electrical activity of the muscle (CMAP) in response to transcutaneous stimulation of the motor nerve with gradual changes in stimulus intensity. Large MUs, including those that result from collateral reinnervation, appear in the CMAP scan as so-called steps, i.e., clearly visible jumps in CMAP amplitude. The CMAP scan also provides information on nerve excitability. This study aims to evaluate the influence of the stimulation protocol used on the CMAP scan and its quantification.

Methods

The stimulus frequency (1, 2 and 3 Hz), duration (0.05, 0.1 and 0.3 ms), or number (300, 500 and 1000 stimuli) in CMAP scans of 23 subjects was systematically varied while the other two parameters were kept constant. Pain was measured by means of a visual analogue scale (VAS). Non-parametric paired tests were used to assess significant differences in excitability and step variables and VAS scores between the different stimulus parameter settings.

Results

We found no effect of stimulus frequency on CMAP scan variables or VAS scores. Stimulus duration affected excitability variables significantly, with higher stimulus intensity values for shorter stimulus durations. Step variables showed a clear trend towards increasing values with decreasing stimulus number.

Conclusions

A protocol delivering 500 stimuli at a frequency of 2 Hz with a 0.1 ms pulse duration optimized CMAP scan quantification with a minimum of subject discomfort, artefact and duration of the recording. CMAP scan variables were influenced by stimulus duration and number; hence, these need to be standardized in future studies.