Electromyography ( EMG ) is an electrodiagnostic treatment technique for evaluating and recording the electrical activity generated by the skeletal muscle. EMG is performed using an instrument called electromyograph to produce a recording called electromyogram . The electromyograph detects the electrical potential generated by the muscle cells when these cells are electrically or neurologically activated. Signals can be analyzed to detect medical abnormalities, activation rates, or recruitment sequences, or to analyze the biomechanics of human or animal movements.
Video Electromyography
Medical use
EMG testing has a wide range of clinical and biomedical applications. EMG is used as a diagnostic tool to identify neuromuscular disease, or as a research tool for studying kinesiology, and motor control disorders. EMG signals are sometimes used to guide injection of botulinum toxin or phenol into the muscle. The EMG signal is also used as a control signal for prosthetic devices such as prosthetic hands, arms, and lower extremities.
An acceleromyograph may be used for neuromuscular monitoring of general anesthesia with neuromuscular inhibitors, to avoid postoperative postoperative curarization (PORC).
Except in the case of some pure myopathic conditions, EMG is usually performed with other electrodiagnostic drug tests that measure the function of neuralgia. This is called the study of nerve conduction (NCS). EMG and NCS needles are usually indicated when there is pain in the legs, weakness of spinal cord compression, or concern about some other neurological disorders or disorders. Spinal cord injuries do not cause neck, back pain or lower back pain, and for this reason, evidence has not shown EMG or NCS to assist in diagnosing the cause of axial lumbar pain, chest pain, or cervical spine pain. EMG needle can help with the diagnosis of nerve compression or injury (such as carpal tunnel syndrome), nerve root injury (such as sciatica), and with other problems of muscle or nerve. Less common medical conditions include amyotrophic lateral sclerosis, myasthenia gravis, and muscular dystrophy.
Maps Electromyography
Technique
Skin preparation and risk
The first step before the insertion of the needle electrode is the preparation of the skin. This usually only cleans the skin with an alcohol bed.
The actual placement of the needle electrode can be difficult and depends on a number of factors, such as specific muscle selection and muscle size. Appropriate EMG needle placement is essential for accurate representation of attractive muscles, although EMG is more effective in superficial muscles because it is unable to bypass the potential of shallow muscle action and detect deeper muscles. Also, the more a person's body fat, the weaker the EMG signal. When placing the EMG sensor, the ideal location is in the abdominal muscles: the midline is elongated. The muscle stomach may also be regarded as being between the motor point (center) of the muscle and the tendonus insertion point.
Pacemakers and heart defibrillator implants (ICDs) are increasingly being used in clinical practice, and there is no evidence to suggest that conducting routine electrodiagnostic studies in patients with this device poses a safety hazard. However, there are theoretical concerns that electrical impulses from neural conduction studies (NCS) can be mistakenly perceived by the device and produce undesirable inhibition or trigger the output or reprogramming of the device. In general, the closer the stimulation site to the pacemaker and the pacing of leads, the greater the chance to induce an amplitudo voltage sufficient to inhibit pacemakers. Despite such concerns, no immediate or delayed side effects have been reported with routine NCS.
There are no known contraindications to perform EMG needles or NCS in pregnant patients. In addition, no complications from this procedure have been reported in the literature. Potential tests, also, have not been reported to cause problems when performed during pregnancy.
Patients with lymphedema or patients at risk for lymphedema are routinely warned to avoid percutaneous procedures in affected limbs, ie venipuncture, to prevent progression or worsening of lymphedema or cellulitis. Despite potential risks, evidence for such complications after venipuncture is limited. No published reports of cellulitis, infections, or other complications associated with EMG were performed in the lymphedema setting or previous lymph node dissection. However, given the unknown risk of cellulitis in patients with lymphedema, reasonable precautions should be made in performing needle examination in the lymphedematous area to avoid complications. In patients with rough edema and taut skin, a skin prick by needle electrodes can cause chronic crying of serous fluid. Potential bacterial media such as serous fluid and skin integrity violations can increase the risk of cellulitis. Before proceeding, clinicians should consider the potential risk of doing research with the need to obtain the information obtained.
Surface and intramuscular EMG recording electrodes
There are two types of EMG: EMG surface and intramuscular EMG. The EMG surface assesses muscle function by recording muscle activity from the surface above the muscle on the skin. The surface electrode can only provide a limited assessment of muscle activity. The EMG surface can be recorded by a pair of electrodes or by a more complex array of several electrodes. More than one electrode is required because EMG recordings show potential differences (voltage differences) between two separate electrodes. The limitation of this approach is the fact that the recording of the surface electrode is confined to the superficial muscles, influenced by the depth of the subcutaneous tissue at the site of record which can vary greatly depending on the patient's weight, and can not distinguish between the release of adjacent muscles.
Intramuscular EMG can be performed using different types of different recording electrodes. The simplest approach is the monopolar needle electrode. This can be a fine wire that is inserted into the muscle with a surface electrode for reference; or two fine wires inserted into the muscles referred to each other. The most common wire records are for research or kinesiology studies. Diagnostics of monopolar EMG electrodes are usually isolated and rigid enough to penetrate the skin, with only the affected ends using surface electrodes for reference. Therapeutic botulinum or phenol therapeutic injection needles are usually monopolar electrodes that use surface references; in this case, however, the metal needle rods of hypodermic, isolated so that only the affected ends, are used both for recording signals and injecting. A slightly more complex design is a concentric needle electrode. These needles have fine wire, embedded in an insulating layer that fills the hypodermic needle barrel, which has an open axis, and the shaft functions as a reference electrode. The open end of the fine wire serves as the active electrode. As a result of this configuration, signals tend to be smaller when recorded from concentric electrodes than when recorded from monopolar electrodes and the signal is more resistant to electrical artifacts from the network and the measurements tend to be more reliable. However, since the stem is exposed along its length, shallow muscle activity can contaminate deeper muscle recordings. EMG single needle electrode electrodes are designed to have very small recording areas, and allow the release of individual muscle fibers to be discriminated against.
To perform an intramuscular EMG, usually either a monopolar or concentric needle electrode is inserted through the skin into the muscle tissue. The needle is then transferred to several points within the relaxed muscle to evaluate both the insertion activity and the resting activity in the muscle. Normal muscle shows short bursts of muscle fiber activation when stimulated by needle movement, but this rarely lasts more than 100ms. The two most common types of resting activity in the muscle are fasciculations and potential fibrillation. The fasciculated potential is the unconscious activation of motor units within the muscle, sometimes seen with the naked eye as a muscle twitch or by a surface electrode. Fibrillation, however, is only detected by EMG needles, and represents the isolation activated from individual muscle fibers, usually as a result of nerve or muscular disease. Often, fibrillation is triggered by needle movement (inserti- tional activity) and persists for a few seconds or more after the movement stops.
After assessing rest and inserti- tional activity, the electromyographer assessed muscle activity during voluntary contraction. The shape, size, and frequency of the resulting electrical signals are assessed. Then the electrode is drawn a few millimeters, and again its activity is analyzed. This is repeated, sometimes until data on 10-20 motor units have been collected to draw conclusions about the functions of motor units. Each electrode track only provides a localized overview of all muscle activity. Because skeletal muscles differ in inner structures, electrodes must be placed in various locations to obtain an accurate study.
Single fiber electromyography assesses the delay between the contraction of individual muscle fibers in the motor unit and is a sensitive test for dysfunction of the neuromuscular junction caused by drugs, toxins, or diseases such as myasthenia gravis. This technique is complicated and usually only done by individuals with special advanced training.
EMG surfaces are used in a number of settings; for example, at a physiotherapy clinic, muscle activation is monitored using surface EMG and patients have a visual or visual stimulus to help them know when they activate the muscle (biofeedback). A review of the surface literature on EMG published in 2008 concludes that surface EMG may be useful for detecting the presence of neuromuscular disease (grade C rating, class III data), but there is insufficient data to support its usefulness to distinguish between neuropathic and myopathic conditions or for diagnosis of specific neuromuscular disease. EMGs may be useful for additional fatigue studies associated with post-poliomyelitis syndrome and electromechanical function in myotonic dystrophy (grade C rating, class III data).
Certain US states limit the performance of EMG needles by non-physicians. New Jersey states that it can not be delegated to a physician's assistant. Michigan has passed a law stating that EMG needles are a medical practice. Specific training in diagnosing medical illness with EMG is required only in residency and fellowship programs in neurology, clinical neurophysiology, neuromuscular medicine, and physical medicine and rehabilitation. There are certain subspecialis in otolaryngology who have undergone selective training in performing laryngeal lymphocyte EMG, and subspecialties in urology, obstetrics and gynecology who have undergone selective training in performing EMG muscles that control bowel and bladder function.
Maximum voluntary contraction
One of the basic functions of EMG is to see how well muscles can be activated. The most common way that can be determined is by performing the maximum voluntary contraction (MVC) of the muscle under test.
Muscle strength, measured mechanically, is usually highly correlated with the size of EMG activation of the muscle. Most commonly it is assessed with surface electrodes, but it must be admitted that these are usually only noted from the muscle fibers in a close-to-surface approach.
Some analytical methods for determining muscle activation are usually used depending on the application. The use of the average EMG activation or peak contraction score is a contentious topic. Most studies generally use maximum voluntary contraction as a means of analyzing the peak strength and strength generated by the target muscles. According to the article, Peak and improved average EMG measurements: Which method of data reduction should be used to assess core exercise ?, concluding that "average improved EMG data (ARV) is significantly less variable when measuring muscle core muscle activity compared with peak EMG variables. "Therefore, these researchers would suggest that" EMG EMG data should be noted along with EMG peak size when assessing core exercise. " Providing readers with both sets of data will result in enhanced validity of the research and potentially eradicate contradictions in research.
More measurements
EMG can also be used to show the amount of fatigue in the muscle. The following changes in the EMG signal can signal muscle fatigue: an increase in the absolute value of the signal average, increased amplitude and duration of muscle action potential and overall shift to lower frequencies. Monitoring of different frequency changes changes the most common ways of using EMG to determine the level of fatigue. Lower conduction velocities allow the slower motor neurons to remain active.
A motor unit is defined as a motor neuron and all the muscle fibers that are innervated. When a motor unit is on, the drive (called the action potential) is carried down the motor neuron to the muscle. The area where the muscular contact nerve is called the neuromuscular junction, or the motor end plate. Once the action potential is transmitted across the neuromuscular junction, the action potential is generated on all innervated muscle fibers of a given motor unit. The sum of all these electrical activities is known as the motor unit action potential (MUAP). This electrophysiological activity of some motor units is a signal that is usually evaluated during EMG. The composition of motor units, the number of muscle fibers per motor unit, the metabolic types of muscle fibers and many other factors affect the potential shape of motor units in the miogram.
Neural conduction tests are also often performed in conjunction with EMG to diagnose neurological diseases.
Some patients may find the procedure somewhat painful, while others experience only slight discomfort when the needle is inserted. The muscle or muscle being tested may be slightly sore for a day or two after the procedure.
EMG signal decomposition
The EMG signal basically consists of the action potential of the superimposed motor unit (MUAPs) of some motor units. For a thorough analysis, measurable EMG signals can be decomposed into their constituent MUAP. MUAPs of different motor units tend to have different shape characteristics, while MUAPs recorded by the same electrode of the same motor unit are usually similar. The size and shape of the MUAP depends mainly on the location of the electrodes on the fibers and may look different if the electrodes move position. EMG decomposition is not trivial, although many methods have been proposed.
EMG signal processing
Rectification is the translation of a raw EMG signal to a signal with a single polarity, usually positive. The purpose of improving the signal is to make sure the signal is uneven to zero, because the raw EMG signal has both positive and negative components. Two types of rectification are used: full wave rectification and half wave. Full wave reporting adds an EMG signal below the baseline to the signal above the baseline to make the conditioned signal all positive. If the baseline is zero, this is equivalent to taking the absolute value of the signal. This is the preferred rectification method because it saves all the signal energy for analysis. Half-wave rectification removes part of the EMG signal that is below the baseline. Thus, the average data is no longer zero because it can be used in statistical analysis.
Limitations
EMG needles used in clinical settings have practical applications such as helping to find the disease. EMG needle has its limitations, however, because it involves voluntary muscle activation, and is therefore less informative in patients who are unwilling or unable to work together, children and infants, and in individuals with paralysis. The EMG surface can have limited applications due to inherent problems associated with EMG surfaces. Adipose tissue (fat) may affect EMG recording. Studies show that adipose tissue increases the active muscle directly beneath the declining surface. As the adipose tissue increases, the EMG signal amplitude of the surface directly above the active muscle center decreases. EMG signal recording is usually more accurate with individuals who have lower body fat, and more compliant skin, such as young people when compared to older ones. Cross-talk muscle occurs when the EMG signal from one muscle interferes with the other from the signal reliability of the tested muscle. The EMG surface is limited due to the lack of deep muscle reliability. Deep muscles need intrusive and painful intramuscular wire to achieve EMG signals. The EMG surface can only measure the shallow muscles and even then it is difficult to narrow the signal to a single muscle.
Electrical characteristics
The source of electricity is a muscle membrane potential of about -90 mV. The measured EMG potential ranges from less than 50 °, Â ° V and up to 20-30 mV, depending on the muscle being observed.
The typical repetition rate of the motor drive unit of the muscle is about 7-20 Hz, depending on the size of the muscles (the eye muscles versus the seat muscles (gluteal)), previous axonal damage and other factors. Damage to motor units can be estimated in the range between 450 and 780 mV.
Results of procedure
Normal results
Resting muscle tissue is usually not electrically active. After the electrical activity caused by the insertion of the insertion needle subsided, the electromyograph should detect no abnormal spontaneous activity (ie, the resting muscle must be electrically silent, with the exception of the neuromuscular junction area, which, under normal circumstances, is very spontaneously active). When muscles are voluntarily contracted, potential action begins to emerge. As the strength of muscle contraction increases, the more muscle fibers generate the action potential. When muscles are fully contracted, there must be an irregular group of potential actions with varying degrees and amplitudes (complete recruitment and interference patterns).
Abnormal results
The EMG findings vary with the type of disorder, the duration of the problem, the age of the patient, the extent to which the patient can cooperate, the type of needle electrode used to study the patient, and sampling error in terms of the number of areas studied in one muscle and the total muscle quantity studied overall. Interpreting EMG findings is usually best done by an individual informed by a focused history and physical examination of the patient, and along with the results of other relevant diagnostic studies conducted including the most important, neural conduction studies, but also, where necessary, imaging studies such as MRI and ultrasound, muscle and nerve biopsy, muscle enzymes, and serological studies.
Abnormal results may be caused by the following medical conditions (please note that this is not a complete list of conditions that can result in abnormal EMG studies):
History
The first documented experiment dealing with EMG began with the works of Francesco Redi in 1666. Redi found the highly specialized muscle of electric ray fish (Electric Eel) generating electricity. In 1773, Walsh had been able to show that the eel muscle tissue could produce electric sparks. In 1792, a publication titled De Viribus Electricitatis in Motu Musculari Commentarius appeared, written by Luigi Galvani, in which the author shows that electricity can initiate muscle contraction. Six decades later, in 1849, Emil du Bois-Reymond discovered that it was also possible to record electrical activity during voluntary muscle contractions. The first actual recording of this activity was made by Marey in 1890, who also introduced the term electromyography. In 1922, Gasser and Erlanger used an oscilloscope to show electrical signals from muscles. Due to the stochastic nature of the myoelectric signal, only rough information can be obtained from its observations. The ability to detect electromyographic signals increased steadily from the 1930s to the 1950s, and the researchers began to use better-wider electrodes to study muscles. AANEM was formed in 1953 as one of several active medical communities with a special interest in advancing the science and clinical use of this technique. The clinical use of surface EMG (sEMG) for the treatment of more specific disorders began in the 1960s. Hardyck and his researcher were the first practitioners (1966) to use sEMG. In the early 1980s, Cram and Steger introduced a clinical method for scanning various muscles using an EMG detection device.
It was not until the mid-1980s that the integration technique in the electrode had been advanced enough to enable the production of the required small and light instrumentation batches and amplifiers. Currently, a number of suitable amplifiers are commercially available. In the early 1980s, cables that produced signals within the desired microvolt range became available. Recent research has resulted in a better understanding of the recording properties of EMG surfaces. Surface electromyography is increasingly used for recording of superficial muscles in clinical or kinesiological protocols, where intramuscular electrodes are used to investigate the muscles in or local muscle activity.
There are many applications for EMG use. EMG is used clinically for the diagnosis of neurological and neuromuscular problems. It is used diagnostically by a gait laboratory and by physicians trained in biofeedback or ergonomic assessment. EMG is also used in many types of research laboratories, including those involved in biomechanics, motor control, neuromuscular physiology, movement disorders, postural control, and physical therapy.
Research
EMG can be used to sense the activity of isometric muscles in which no movement is produced. This allows the class definition of subtle motion to control the interface without being noticed and without disturbing the surrounding environment. These signals can be used to control the prosthesis or as control signals for electronic devices such as cell phones or PDAs.
The EMG signal has been targeted as a control for the flight system. The Human Senses Group at the NASA Ames Research Center in Moffett Field, CA is trying to advance a human-machine interface by directly connecting a person to a computer. In this project, EMG signals are used to replace the mechanical and keyboard joysticks. EMG has also been used in research on "useable cockpits," which use EMG-based motions to manipulate switches and control rods needed for flight simultaneously with goggle-based displays.
Speech recognition recognizes speech by observing EMG activity from speech-related muscles. It's targeted for use in noisy environments, and may be useful for people without vocal cords and people with aphasia.
EMG has also been used as a control signal for computers and other devices. EMG-based interface devices can be used to control moving objects, such as car robots or electric wheelchairs. This may be useful for individuals who can not operate a controlled joystick wheelchair. EMG surface tape can also be an appropriate control signal for some interactive video games.
In 1999, an EMG program called Echidna was used to allow a man with locked syndrome to send messages to a computer. The program, now called NeuroSwitch, developed by Control Bionics allows people with serious disabilities to communicate via text, email, SMS, computer-generated voice and to control computer games and programs, and - over the internet - robot robots long distance Anybots.
A joint project involving Microsoft, the University of Washington in Seattle, and the University of Toronto in Canada have been explored using muscle signals from hand gestures as interface devices. The patent based on this study was submitted on 26 June 2008.
See also
- Chronaxie
- Potential muscle action of the compound
- Electrical muscle stimulation
- Electrodiagnostic drugs
- Electromyoneurography
- Magnetography
- Neural conduction study
- Neuromuscular ultrasound
- Phonography
References
Further reading
- Piper, H.: Elektrophysiologie menschlicher Muskeln . Berlin, J. Springer, 1912.
External links
- Canadian Electromyography Technology Association (AETC)
- MedlinePlus posts on EMG describes EMG
- Neuromuscular.edu
- American Neuromuscular & amp; Electrodiagnostic Drugs
- EmedicineHealth page at EMG
- Risks in Electrodiagnostic Treatment
- Interactively design application of RMS envelope measurement of EMG process with ASN Filter Designer (ASN-AN024)
Source of the article : Wikipedia
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