Electromyographic Signs Research Articles

Presymptomatic spondylotic cervical cord compression.

We conducted a cohort study of clinically asymptomatic spondylotic cervical cord compression cases with the primary end point of the development of clinical signs of cervical myelopathy. To investigate whether various demographic, clinical, radiologic, and electrophysiological parameters could predict progression from clinically asymptomatic (preclinical) spondylotic cervical cord compression to symptomatic myelopathy. The data available on the prediction of the outcome in surgical and conservative treatment of spondylotic cervical myelopathy are controversial. Little is known about the clinical natural history of asymptomatic magnetic resonance image-detected spondylotic cervical cord compression and/or changes of signal intensity. A group of 66 patients (32 women, 34 men, median age 50 years) with magnetic resonance signs of spondylotic cervical cord compression but without clear clinical signs of myelopathy was followed prospectively for at least 2 years (range, 2-8 years; median, 4 years). Various demographic, clinical, imaging, and electrophysiological parameters were correlated with clinical outcome. Clinical signs of myelopathy during the follow-up period were detected in 13 patients (19.7%). The only variables significantly associated with the development of clinically symptomatic spondylotic cervical myelopathy (SCM) were the presence of symptomatic cervical radiculopathy, electromyographic signs of anterior horn lesion, and abnormal somatosensory-evoked potentials. A multivariate logistic regression model based on these variables correctly classified 90% of cases into 2 subgroups: a group with development of symptomatic SCM and that without clinical manifestation of subclinical cervical cord compression. Electrophysiological abnormalities together with clinical signs of cervical radiculopathy could predict clinical manifestation of preclinical spondylotic cervical cord compression.

Absence Of A Slow Component Of Pulmonary VO2 Kinetics In Very Old Subjects

0099 PURPOSE: The effects of aging on skeletal muscle oxidative metabolism, and in particular on O2 uptake (VO2) kinetics were evaluated in 28 elderly (E) (78.1±3.8 yrs, mean±SD) and 7 young (Y) (28.4±5 yrs) subjects. METHODS: After an incremental exercise to voluntary exhaustion on a cycloergometer, to evaluate peak VO2 and ventilatory threshold (VT), the subjects carried out 6 min constant-load exercises below (<VT) and above VT (>VT). Pulmonary VO2 was determined breath-by-breath. Vastus lateralis oxygenation was determined by near-infrared spectroscopy, and changes in deoxygenated hemoglobin + myoglobin concentration Δ[deoxy(Hb+Mb)] were taken as a muscle oxygenation index. Vastus lateralis surface electromyography (EMG) was also recorded. RESULTS: VO2peak in E (1.188±0.37 L·min −1) was about 50% lower (p<0.001) than in Y (2.404±0.80 L·min−1). The time constant of the primary component of VO2 kinetics was higher (p<0.05) in E than in Y, both <VT (46.29±14.8 vs. 31.59±8.3 s) and >VT (59.67±17.3 vs. 33.04±4.3 s). Differently from Y, E did not show a slow component of VO2 kinetics for >VT. The root mean square (RMS) calculated from the EMG signal was positively related to time in both groups during >VT; during <VT, RMS was positively related to time only in E. A slow component of Δ[deoxy(Hb+Mb)] kinetics, during >VT, was observed in 5 Y and in 1 E. CONCLUSIONS: We confirm the lower VO2peak and slower VO2 kinetics with aging. Elderly subjects do not show a slow component of VO2 kinetics during constant-load exercise >VT, even in the presence of EMG signs of fatigue. This could be explained by a preferential atrophy of type II fibers, or to a reduced differentiation between fiber types in aging. Financial support by EC Contract QLK6-CT-2001-00323 (“Better-Ageing”) is acknowledged.

Absence Of A Slow Component Of Pulmonary VO2 Kinetics In Very Old Subjects

0099 PURPOSE: The effects of aging on skeletal muscle oxidative metabolism, and in particular on O2 uptake (VO2) kinetics were evaluated in 28 elderly (E) (78.1±3.8 yrs, mean±SD) and 7 young (Y) (28.4±5 yrs) subjects. METHODS: After an incremental exercise to voluntary exhaustion on a cycloergometer, to evaluate peak VO2 and ventilatory threshold (VT), the subjects carried out 6 min constant-load exercises below (<VT) and above VT (>VT). Pulmonary VO2 was determined breath-by-breath. Vastus lateralis oxygenation was determined by near-infrared spectroscopy, and changes in deoxygenated hemoglobin + myoglobin concentration Δ[deoxy(Hb+Mb)] were taken as a muscle oxygenation index. Vastus lateralis surface electromyography (EMG) was also recorded. RESULTS: VO2peak in E (1.188±0.37 L·min −1) was about 50% lower (p<0.001) than in Y (2.404±0.80 L·min−1). The time constant of the primary component of VO2 kinetics was higher (p<0.05) in E than in Y, both <VT (46.29±14.8 vs. 31.59±8.3 s) and >VT (59.67±17.3 vs. 33.04±4.3 s). Differently from Y, E did not show a slow component of VO2 kinetics for >VT. The root mean square (RMS) calculated from the EMG signal was positively related to time in both groups during >VT; during <VT, RMS was positively related to time only in E. A slow component of Δ[deoxy(Hb+Mb)] kinetics, during >VT, was observed in 5 Y and in 1 E. CONCLUSIONS: We confirm the lower VO2peak and slower VO2 kinetics with aging. Elderly subjects do not show a slow component of VO2 kinetics during constant-load exercise >VT, even in the presence of EMG signs of fatigue. This could be explained by a preferential atrophy of type II fibers, or to a reduced differentiation between fiber types in aging. Financial support by EC Contract QLK6-CT-2001-00323 (“Better-Ageing”) is acknowledged.

EMG signs of neuromuscular fatigue related to the ventilatory threshold during cycling exercise.

We questioned whether electromyographic (EMG) signs of neuromuscular fatigue accompany the changes in respiratory variables measured at the ventilatory threshold (VTh) during exercise on a cycloergometer. This was based on the assumption that the activation of muscle afferents sensitive to accumulation of lactate and potassium is suspected to elicit both the EMG signs of fatigue and hyperventilation. In 39 subjects performing an incremental cycling, the EMG estimates of neuromuscular fatigue in vastus lateralis were a non-linear increase in root mean square (RMS), a decrease in median frequency (MF), a non-linear increase in low-frequency EMG energies (EL), and/or a decrease in high-frequency energies (EH). VTh was determined from a non-linear increase in VCO2 [VTh(VCO2 slope)] and an increased value of the respiratory equivalent for oxygen [VTh(VE/VO2)]. We measured a significant increase in venous blood concentration of lactate and potassium, and a significant pHv fall at VTh. One EMG estimate of fatigue was detected in 33/39 individuals and two EMG estimates in 17 subjects. Highly significant positive correlations were found between the oxygen uptakes corresponding to each EMG estimate and to each detection criterion of VTh. These observations suggest that the activation of muscle sensory pathways contribute to the mechanism of VTh.

EVALUATION OF BLOOD FLOW DISTURBANCES IN DIABETIC PATIENTS BY LASER DOPPLER FLOWMETRY

Background. The aim of this study was to investigate patients with non-insulin dependent diabetes by laser Doppler flowmetry in order to asses changes in the peripheral flow regulation during hemodynamics tests as evidence of impaired auto-regulation of the microcirculation. Methods. 2 groups of subjects were incorporated in the study. The first group included 20 patients with diabetes without electromyographical signs of neuropathy and without peripheral arterial occlusive disease while the second (control) group included 20 healthy subjects. Microcirculation investigations were carried out at rest and after hemodynamics tests. Blood flow was measured using a laser Doppler flowmetry. Changes in the flow minus the »biological zero« value were measured after 3 minutes of artificial arterial occlusion, after deep inspiration and by experimental venous hypertension (40 and 70 mm Hg) which was used to provoke venoarteriolar reflex. Results. Resting flow was significantly higher in diabetic patients compared to the healthy subjects (p < 0.01). The vasoconstrictor response to deep inspiration and experimental venous hypertension, cuff pressure 40 mm Hg, was significantly impaired in diabetic patients as compared to the healthy subjects (p < 0.001 vs. p < 0.01). The maximal hyperemia after artificial arterial occlusion was significantly reduced in diabetic patients in comparison with the healthy controls (p < 0.01). Conclusions. Laser Doppler flowmetry provides a non-invasive technique for evaluating microcirculating disturbances at a relatively stage in diabetes, long before the initial clinical presentation of peripheral arterial occlusive disease or neuropathy.

Herpes zoster of the head and limbs: Electroneuromyographic and clinical findings in 158 consecutive cases

Mondelli M, Romano C, Rossi S, Cioni R. Herpes zoster of the head and limbs: electroneuromyographic and clinical findings in 158 consecutive cases. Arch Phys Med Rehabil 2002;83:1215-21. Objectives: To quantify electromyographic and neurographic changes and to correlate them with the clinical data of outpatients with herpes zoster. Design: Prospective case series. Setting: Outpatient department. Patients: A consecutive, unselected series of 158 outpatient cases (88 women, 70 men; mean age, 64y) of herpes zoster of the head and limbs. Interventions: Not applicable. Main Outcome Measures: Blink reflex and electromyography and motor and sensory nerve conduction velocities of nerves and muscles corresponding to affected dermatomes. Results: Postherpetic neuralgia (PHN), segmental zoster paresis, and polyneuropathy were found in 31%, 19%, and 2.5% of cases, respectively. Absence or reduction of sensory action potential amplitudes, blink reflex areas, and compound muscle action potential amplitudes were found in 60%, 31%, and 18% of cases, respectively. Sensory and motor conduction velocities and motor and blink reflex latencies were nearly always normal or only slightly slowed. Electromyographic signs of abnormal spontaneous activity were found in 36% of the cases. Electrophysiologic alterations were correlated among themselves, with age, with presence of segmental zoster paresis, and with absence of antiviral therapy. The extent of the skin rash (number of dermatomes affected by herpes zoster) was the only variable predictive of disappearance or improvement of PHN. Conclusions: Sensory axonal neuropathy, often associated with similar motor involvement, can be shown by classical electrophysiologic methods in herpes zoster. The severity of damage to motor fibers was related to damage to sensory fibers, but no relation was found between peripheral axon damage and PHN. The site of motor system damage may be the ventral roots, plexus, or peripheral nerve. The probability of complications and the severity of sensory and motor peripheral axonal damage were increased in older patients. Appropriate antiviral therapy seems to reduce the incidence of segmental zoster paresis and the severity of damage to the peripheral fibers. A reduced extent of herpetic rash was the only factor to correlate with a good outcome of PHN. © 2002 by the American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation

Local denervation of lumbar paraspinal muscles may not be used as a criterion for the effectivity of radiofrequency lesions of the zygapophyseal joints

AbstractA treatment option in a selected group of patients with chronic non-specific low back pain is percutaneous radiofrequency denervation of lumbar zygapophyseal joints (RDLZJ). These joints and the lumbar paravertebral musculature are innervated by the dorsal rami of the lumbar spinal nerves. It has been stated that the effectiveness of the procedure can be deduced from the finding of electromyographic signs of denervation in the paraspinal muscles. This study was designed to test the following: Does RDLZJ cause spontaneous muscle fibre activity of the paraspinal muscles? Is pain relief after a RDLZJ correlated with the presence of spontaneous activity in the paraspinal muscles?In a prospective observer-blind study, twenty-eight patients with a history of at least one year of chronic low back pain were selected on the basis of a positive response to a diagnostic nerve blockade and subsequently randomly assigned to one of two treatment groups. Each patient in the RF treatment-group (14 patients) recei...

Outcome of surgery for cervical radiculopathy evaluated by determination of trapezius muscle microcirculation and electromyography

Surgery for cervical radiculopathy was evaluated in 27 patients after anterior Cloward procedure (19 patients) or posterior decompression (eight patients). In addition, we examined 10 conservatively treated patients. Each patient was studied prospectively with regards to the effects on microcirculation in the local trapezius muscle during a fatiguing series of stepwise increased contractions. The right and left muscles were simultaneously examined pre-operatively and postoperatively after 9 months using laser-Doppler flowmetry and simultaneous surface electromyography (EMG). Preoperatively, a reduced microcirculation was found in the most painful side compared with the opposite side. This is in accordance with earlier reports on patients with chronic neurogenic neck pain, who also show reduced muscle tension on EMG. Postoperatively, the muscle blood flow became increased, but only in patients operated on via a posterior approach. A tendency at increased EMG-amplitude and reduced mean power frequency of the EMG was noted. These EMG signs of muscle fatigue suggest increased ability to exhaust the trapezius muscle postoperatively. The observed postoperative changes were consistently more frequent in the less painful side. We conclude from these objective measurements showing only a tendency at increased microcirculation and muscle tension postoperatively, that the effect on the trapezius muscle is limited.

Abnormalities of the soleus H-reflex in lumbar spondylolisthesis: a possible early sign of bilateral S1 root dysfunction.

Using routine electrodiagnostic procedures, the authors searched for physiologic evidence of nerve root compromise in patients with chronic mechanical perturbation to the lumbar spine. They examined 37 patients with spondylolisthesis and various degrees of degenerative changes in the lumbar canal. Clinical and neurophysiologic findings were compared with data obtained from 36 healthy persons. The soleus H-reflex appeared to be a sensitive indicator of sensory fiber compromise at the S1 root level, because changes correlated well with the focal sensory signs and preceded clinical and electromyographic signs of motor root involvement. When these occurred, the clinical findings were consistent with a more severe nerve root deficit and with radiographic evidence of neural compression. The greater sensitivity of the soleus H-reflex may be related to the pathophysiologic events that occur at the lesion site.

Tissue Oxygenation and EMG during Computer Mouse Work and Submaximal Isometric Wrist Extensions

Sufficient tissue oxygenation (TO2) is essential for muscle function in general. However, it is not known to which extent TO2 is influenced during different low-level contractions. The aim was to study the interaction between EMG activity and TO2 during computer mouse tasks and submaximal isometric contractions at load levels corresponding to levels that occur during repetitive work in industry. Eight healthy subjects performed multidirectional computer mouse tasks (40 and 60 clicks/min) with the right arm. In addition, 1 -minute isometric wrist extensions at 5, 15 and 25 %Maximal Voluntary Contraction (MVC) were performed. Further, a 15 %MVC wrist extension until exhaustion was performed. Near-infrared spectroscopy was used to measure TO2 of m. extensor carpi radialis. EMG was recorded from m. extensor carpi radialis and m. extensor digitorum. During mousing the EMGRMS activity was in generel higher during the high speed compared to the low speed task. Muscular load of the forearm has isometric characteristics to a high degree. No significant difference in TO2 was found between the two mousing speeds. During the isometric contractions EMGRMS increased and TO2 decreased with increasing contraction level. The mean endurance time at the 15 %MVC wrist extension was 22.6 min. The average exerted force remained constant though fluctuations in the force increased as a function of time, indicating impaired force control due to development of fatigue. During the endurance task the EMGRMS activity increased and the EMGMPF decreased, indicating electromyographic signs of muscle fatigue. Within less than one minute TO2 decreased significantly relative to resting values. No further decrease was seen during the endurance contraction. Point of exhaustion was not related either to a gradual or a sudden decrease in TO2. Although the average exerted force remained constant, sudden changes in EMGRMS was seen in some subjects especially in the last part of the contraction, indicating changes in force distribution between muscles. This is assumed to be a fatigue-preventing mechanism. These changes in extensor carpi radialis muscle activity were reflected as opposite changes in TO2-levels, A cross correlation analysis showed a correlation between in extensor carpi radialis muscle activity and TO2, time displacement=3.4 sec, r=−0.31. This indicates that the changes in EMG activity precede the changes in TO2-level. In conclusion, TO2 was inversely related to muscle activity and exerted force. A steady state level below resting level of TO2 was found during the prolonged fatiguing isometric contraction. Point of exhaustion could not be explained either by a gradual or a sudden decrease in TO2.

Pressure pain thresholds and electromyographically defined muscular fatigue induced by a muscular endurance test in normal women.

This study was undertaken to examine the relation between muscular tenderness measured as pressure pain thresholds (PPTs) and electromyographic (EMG) signs of fatigue before and after a local standardized static muscle contraction. Pressure pain thresholds were measured in the shoulder region before, immediately after, and 10 minutes after a standardized static endurance test while monitoring the EMG signs of local muscular fatigue and its recovery. The study did not address local biochemical issues. The study was conducted at the Department of Rehabilitation, Lund University Hospital, Lund, Sweden. Twenty-five healthy female volunteers without musculoskeletal problems participated in this study. A static endurance test was performed, which consisted of a submaximal unilateral activation of the right trapezius and deltoid muscles for as long as possible. Bilateral PPTs over the trapezius and deltoid muscles were measured with an electronic pressure algometer. Established surface EMG parameters of local muscular fatigue were assessed. The Borg Rating of Perceived Exertion scale was used. The average endurance time was 330 seconds. Immediately after the test, significant bilateral increases in the normalized PPTs over both muscles were found, although the increase was more pronounced on the test side: over the right trapezius muscle by 13% (p <0.001), over the right deltoid muscle by 23% (p <0.001), and over the left trapezius and deltoid muscles by 6% (p = 0.04) and (p = 0.009), respectively. These increases persisted 10 minutes after the end of the test. The subjects developed significant signs of fatigue as defined by EMG criteria in both muscles on the right side during the test. The recovery from fatigue was approximately half complete 15 seconds after the end of the test and complete or almost complete 10 minutes thereafter. Pressure pain thresholds over shoulder muscles remained elevated up to 10 minutes after a unilateral static endurance test. This time course was completely different from that of EMG-defined muscle fatigue, which showed a fast recovery. These findings indicate that the mechanisms of recovery from fatigue and nociception are independent of each other. The bilateral PPT increases might be explained by central antinociceptive mechanisms activated by static muscle work.

Neuromyotonia in mice with hereditary myelinopathies.

The purpose of this study was to further characterize neuromyotonia in mice with deletions and point mutations of myelin protein genes. Clinical observation showed irregular stretching of the hindlimbs, tremor and generalized myokymia in mice with targeted deletions of the genes encoding myelin protein zero (P0-/-) or peripheral myelin protein 22 (Pmp22-/-), and Trembler mice, which carry a point mutation of Pmp22. By electromyography (EMG), we found irregular high-frequency bursts of spontaneous motor unit activity and rhythmic doublet or multiplet discharges of motor units in these mouse models of human hereditary neuropathies. The EMG signs are typical for neuromyotonia and myokymia, respectively. The activity persisted after a proximal nerve section in many cases, localizing the generator to the peripheral nerve or the muscle. We now show that blocking neuromuscular transmission with suxamethonium abolished the spontaneous activity, ruling out a muscle origin. Phenytoin ameliorated the motor behavior. Taken together, our study shows that neuromyotonia develops in different mouse models of hereditary myelinopathies. This indicates that spontaneous motor unit activity may underlie neuromyotonia, which is occasionally observed in Charcot-Marie-Tooth disease. These animal models will be useful to study the pathogenesis of neuromyotonia.

Reversibility of paraneoplastic bilateral diaphragmatic paralysis after nephrectomy for renal cell carcinoma

Bilateral diaphragmatic paralysis is usually caused by anatomic lesions of both phrenic nerves (e.g., after cardiothoracic surgery), generalized neurologic diseases (e.g., primary motor neuron disease, amyotrophic lateral sclerosis) or is without a known cause (idiopathic). We report a case of a patient with renal cell carcinoma complicated by an isolated bilateral diaphragmatic paralysis without clinical or electromyographic signs of other muscle or nerve involvement. There has been progressive, though till now partial, recovery of his vital capacity rising from 44% to 72% of predicted values, and maximal inspiratory pressures during the two years following the curative resection of his renal cell carcinoma. We believe this is the first report of a paraneoplastic bilateral diaphragmatic paralysis with actual recovery after tumour therapy.

Forma de comienzo respiratorio en la enfermedad de motoneurona

To present a case of respiratory failure as the form of onset of amyotrophic lateral sclerosis, to review the main clinical findings, data of the investigations done which suggest the presence of this disorder and describe its therapeutic management. A 68 year old man presented with a subacute illness characterized by a sleep disorder with sleep fragmentation, snoring of increasing intensity, without clear pauses of apnea, progressive diurnal hypersomnia accompanied by progressive dyspnea followed by respiratory failure with respiratory acidosis and difficulty in manipulating things with his hands. Diagnostic investigations showed a restrictive pattern without pulmonary fibrosis, due to paralysis of the diaphragm, and the presence of electromyographic signs compatible with motorneuron disease. The patient was treated with riluzole 100 mg/day and non-invasive mechanical ventilation and maintained an acceptable quality of life. Motorneuron disease may start with acute or progressive respiratory failure without a clear etiological cause and may appear to be similar to obstructive sleep apnea syndrome. The treatment of choice for this respiratory problem is non-invasive mechanical ventilation. Absence of symptoms of bulbar involvement is essential for a favourable prognosis.

Infantile neuroaxonal dystrophy: clinical spectrum and diagnostic criteria.

To present clinical, neurophysiologic, and neuroradiologic findings in 13 patients with infantile neuroaxonal dystrophy (INAD), focusing on aspects that assist early diagnosis. Clinicopathologic diagnostic criteria for INAD were delineated by Aicardi and Castelein in 1979, but atypical cases are reported frequently and little is known of the diagnostic utility of MRI. The authors reviewed the clinical, neurophysiologic, and MRI findings of 13 patients who met the diagnostic criteria for INAD. Symptoms onset was between 6 months and 2 years of age. In nine patients the clinical course was typical, with rapid motor and mental deterioration; in four patients progression was slower and the clinical picture was different. Electromyographic (EMG) signs of chronic denervation, fast rhythms on EEG and abnormal visual evoked potentials were observed in all patients during the disease course. Cerebellar atrophy with signal hyperintensity in the cerebellar cortex on T2-weighted images were the most characteristic MRI findings; hypointensity in the pallida and substantia nigra was also observed in two patients. alpha-N-acetyl-galactosaminidase activity on leukocytes was normal in the 10 patients tested. EMG and MRI abnormalities are the earliest and most suggestive signs of INAD, which has a clinical and radiologic spectrum that is broader than reported previously.

Spinal cord implantation of avulsed ventral roots in primates; correlation between restored motor function and morphology.

Functional restitution following spinal cord implantation of avulsed ventral roots was assessed electromyographically and correlated with the morphology of the regenerated neural structures in primates. The C5-C8 ventral roots were avulsed from the spinal cord in seven Macaca fascicularis monkeys. In three animals the roots were immediately reimplanted into the ventrolateral part of the spinal cord. In two monkeys the avulsed roots were reimplanted with a delay of 2 months and in two control animals the roots were not reimplanted. There was substantial recovery of function after both immediate and delayed spinal cord implantation of the avulsed ventral roots. The population of neurons that had regenerated was larger than on the control side, indicating a rescue of cells after an immediate root implantation. Different functional types of neurons had been attracted to regrow axons to the implanted root as judged by their position in the ventral horn. Thus, neurons normally supplying antagonistic muscles, such as the triceps muscle, participated in the innervation of the biceps muscle. Functionally this deficient directional specificity was correlated to both spasticity and co-contractions among agonistic and antagonistic muscles. Occasional electromyographic signs of function occurred also in control animals where the avulsed roots had not been implanted. This recovery was found to depend on regrowth from the site of avulsion, within the pia mater among the leptomeningeal cells and to the avulsed roots. The acceptable functional dexterity regained due to corrective surgery is discussed in terms of neurotrophism and plasticity.

The timing of congenital brachial plexus injury: A study of electromyography findings in the newborn piglet

Objective: Permanent congenital brachial plexus palsy is a recognized serious complication associated with shoulder dystocia. The timing and etiology of this injury remains controversial. Previous authorities have used adult-derived, non–brachial plexus data to extrapolate the anticipated timing for electromyographic denervation changes to date such injuries in the newborn. With use of a domestic swine model, this investigation tests the hypothesis that electromyographic evidence of brachial plexus denervation in the newborn is temporally different than that in the adult. Study Design: Five healthy 2-day-old and two adult pigs underwent unilateral sharp transection of the brachial plexus. Daily electromyographic studies were performed in brachial plexus innervated muscle groups on the involved and contralateral (control) front limbs. Postmortem measurements of the transected nerve segments were obtained in one piglet and one adult animal. Representative hard copy recordings of individual electromyographic studies were collected. Results: Immediately after surgical transection of the brachial plexus, no electromyographic evidence of denervation was observed. Uniformly in the newborn piglets, at 24 hours after transection, denervation in the form of fibrillation potentials, positive sharp waves, and complex repetitive discharges was seen. Serial testing demonstrated proximal to distal gradients of denervation over the next 24 to 48 hours. A delay in electromyographic evidence of denervation was observed in the two adult pigs until days 5 and 8, respectively. Control limb studies remained normal throughout the study period. Nerve length measurements for individual muscle groups were as follows for the adult and newborn pigs, respectively: deltoid 11.4 cm, 2.5 cm; cleidobrachialis 16.0 cm, 4.0 cm; triceps 15.5 cm, 4.5 cm; forelimb flexors 26.0 cm, 6.5 cm; and extensor carpi radialis 31.0 cm, 9.0 cm. Conclusion: Electromyographic evidence of brachial plexus denervation after surgical transection differs between the newborn and the adult pig. Consistent with wallerian degeneration, a correlation exists between length of the distal nerve segment and timing for electromyographic signs of denervation. These findings suggest it would be inappropriate to extrapolate the anticipated timing for electromyographic changes in the newborn on the basis of previously established adult non–brachial plexus data. (Am J Obstet Gynecol 1998;178:688-95.)

A Practical Guide to the Recognition and Management of Myasthenia Gravis

Myasthenia gravis is an autoimmune disorder of neuromuscular transmission. It is characterised by muscular weakness and fatiguability. Extrinsic ocular muscles are frequently involved at the onset of the disease; in about 15% of cases clinical signs remain confined to these areas, while in the other patients weakness becomes generalised. Diagnosis relies on clinical history and signs, improvement on anticholinesterase injection, electromyographic signs of impaired neuromuscular transmission and serum antiacetylcholine receptor (anti-AChR) antibody titration. Apart from the anti-AChR antibody assay, no single test is specific for myasthenia gravis; it is rather their combined results that can confirm diagnosis. The therapeutic approach varies from patient to patient and, as far as possible, should be adapted to each individual. Symptomatic drugs such as anticholinesterases improve muscle strength but seldom restore it to normal. Immunosuppressive therapy is very effective but entails the risk of severe adverse effects. Thymectomy improves the course of the disease and can increase remission rate; short term treatments are of benefit in the management of myasthenic emergencies.

Single-fibre laser Doppler flowmetry and electromyography for evaluating microcirculation in forearm muscle during static and continuous handgrip contractions.

A technique is described for intramuscular measurement of muscle blood flow in the forearm, by using a 0.5-mm thin optical single-fibre for laser Doppler flowmetry (LDF) inserted percutaneously. Continuous recordings were performed of the brachioradial muscle during an 11-min series of alternating 1-min periods of increased static contraction and rest determined by an electronic handgrip forcemeter and surface electromyography (EMG) of the muscle. Stepwise increased handgrip contractions were performed at 10%, 20%, 30%, 40% and 50% maximal voluntary contraction (MVC). This was followed by a similar series of continuous contractions. Finally, an endurance test was performed with a handgrip force of 50% MVC maintained for as long as possible. A group of ten healthy men of different ages was studied. Signal processing was done on line by computer. Successive increases in rootmean square (rms)-EMG and a fall in the mean power frequency (MPF) of the EMG spectrum occurred during the series of static contractions, which evoked perceived local fatigue in the forearm. Muscle blood flow recorded simultaneously showed no change from resting level during contractions at 10%, 20% and 30% MVC, while at 40% and 50% MVC mean increases of 150% and 200% were recorded. Blood flows measured during the rest periods showed large variability with no significant changes. This was also found after continuous contractions of the same intensities. The endurance time was 1.2-3.5 min (mean 2.4 min). Muscle blood flow showed mean increases of 214%, 256% and 229% of resting level each minute of the maintained contraction. Nevertheless, EMG signs of local fatigue developed, such as a rise in rms-EMG and a fall in MPF, and the subject experienced local fatigue. To conclude, this technique of percutaneous, continuous LDF recorded, at high sensitivity, the microcirculation at different fluxes and EMG-defined muscle activity.

Work load during floor cleaning. The effect of cleaning methods and work technique.

Cardiovascular and muscle load levels were evaluated during floor cleaning. A group of 12 experienced female cleaners participated in the study. Of the subjects 6 used a mopping method and 6 a traditional scrub and cloth method. Heart rate, oxygen consumption, rating of perceived exertion, electromyography from the trapezius muscle and video recordings were obtained during floor cleaning. With respect to relative heart rate and oxygen consumption the two groups did not differ. The results revealed a high cardiovascular load corresponding on average to 53 percent of the individual maximal oxygen uptake. In addition 65 percent of the observed period was spent with the back in a position forward flexed more than 20 degrees C. The time spent in extreme forward back flexion was shorter for the mopping group. Both groups exhibited high static, median and peak shoulder muscle load levels of 10 percent, 25 percent and 54 percent maximal voluntary contraction, respectively. At the same time, however, the mopping group tended to have a higher shoulder load than the group using the scrub and cloth method. Furthermore, electromyographic signs of fatigue in the trapezius muscle indicated a more stereotype activation of the shoulder muscles during mopping than during scrubbing. Based on these results, it was concluded that mopping cannot be recommended as less strenuous than scrubbing.