Electromyography

Electromyography is a method of learning bioelectric processes developing in the muscles of people and animals during various motor reactions. The method is based on recording of biopotentials skeletal muscles. Account fluctuations muscle potentials (Fig) is a special instrument - electromyography different types.
Although electromyograms reflect only fluctuating potentials that develop directly in the muscle, still in their qualitative and quantitative characteristics can be judged also on normal or pathological condition of the Central nervous system, regulating all kinds of motive activity of man. In various diseases there are a variety of violations normal picture electromyograms (Fig).
electromyogram

Electromyogram while reducing the overall finger extensor: A - OK; B - in severe muscle paresis after polio; In - parkinsonism shake and rigid increase of a tone.


When myogenic violations (myositis, myopathy) are identified by asynchronous oscillations with high frequency, shortening the duration of oscillations. In cases of advanced muscle atrophy there is a decrease in the amplitude of oscillations.
When denervation muscles appear pathological oscillations:
low-voltage (usually two - and three-phase) potentials fibrillyatsy.
When segmental nuclear appearances and amyotrophy (defeat of motor cells of the brain stem and spinal cord), the decrease of the electrical activity, sometimes to "bioelectric of silence", a rare appearance of oscillations of the potential fibrillyatsy.
When newsegmentonly disorders (Central paralysis, hyperkinesia) revealed a decrease in the amplitude of oscillations in EMG affected muscles, asynchronous excitation of motor cells and muscle fibers.
Mapping electromyographic and clinical data allows you to specify the place (localization) and the severity of injuries of the nervous system and muscles. Comparison of re-recorded in the same muscle of electromyogram helps detect improvement (recovery) of its functional condition or impairment (severe disease), and also serves as a basis for objective evaluation of the results of the treatment.
EMG data can provide substantial help in the diagnosis of early stages of the disease and lung damage neuromotor system: arise in such cases, musculoskeletal disorders are sometimes so insignificant that clinical examination them still does not detect, whereas electromyograms registered a highly sensitive device, already reflect the pathological electrical activity of muscles.
Electromyography is widely used not only in the neurological clinic, but also in other human diseases (cardiovascular, cancer, infectious and other).

Electromyography (from the Greek. mys, myos - muscle, grapho - write) - check the electrical potentials; skeletal muscles. Electromyography is used as a method of study of normal and impaired function of the musculoskeletal system of humans and animals. Electromyography includes methods for the study of the electrical activity of the muscles in the rest, at random, spontaneous and induced artificial irritation reductions.
Using electromyography study the functional state and functional features of muscle fibres, motor units, neuromuscular transmission, nerve trunks, segmental apparatus of the spinal cord, and newsegmentonly structures, study the coordination of movements, development of impellent skills for different types of work and athletic exercises, restructuring of the work of the transplanted muscle fatigue. On the basis of electromyography established method for control currents of muscles, which has found practical application in the management of the so-called bioelectric prostheses (see Prosthetics).
Electromyogram curve produced on photographic paper, film, or on paper at the Desk electrical potentials of skeletal muscles. It can be recorded using a special device, called a computer, or other equipment used for the registration of action potentials. The device usually has at least two channels recording. Each channel includes the discharge electrodes, power biopotential and recording device. In most electromyographs provides a device for visual and auditory control (Fig. 1).

Fig. 1. Diagram of the device for electromyography.

The main source of fluctuations of the electric potential of the muscles is spreading over the muscle fibers of the excitation process. However, because electromyogram is logged in the field of motor points (see the electric diagnostics), part of the electric potential is the potential arising from the excitement of end plates. Electric potentials skeletal muscles is possible to allocate intracellular or extracellular.
Intracellular recording of electric potentials of individual muscle fibers of the person allows to identify those characteristics that were previously studied under the microelectrode animal studies or drugs: value of membrane potentials of muscle fibers, depolarization and giperpoliarizatia membranes and so on (see Bioelectrical phenomena). Registration intracellular potential skeletal muscles a number of authors calls intracellular electromyography.
Extracellular abstraction electric potential conduct by two methods:
1) by means of electrodes with a relatively small lateral surface (hundredths of a square millimeter), dip into the muscle through needles (Fig. 2, 1-3); in all cases, except unipolar lead, both discharge electrodes are located a short distance from each other (typically less than 0.5 mm); 2) by means of electrodes with a relatively large lateral surface (30 - 100 mm2), is usually placed on the skin over the muscles at a relatively great distance from each other (1-2 cm) (Fig. 2, 4-6). In the first case, to talk about a "local", and the second is "global" leads. "Local" abstraction allows the study of the electric potential, resulting in a small amount of muscle tissue: potentials of individual motor unit, the total potential of a small number of motor units, in conditions of a pathology - potentials of individual muscle fibers. The main object of study is the propulsion unit. This term originally meant a set of muscle fibers, innerved by one motoneuronal.

Fig. 2. Needle and cutaneous electrodes for registration of electromyogram: 1 - concentric; 2 - bipolar; 3 - multielectrode (Bahtalo); 4 - 6 - skin electrodes of different types.
Fig. 3. The oscillations of the potential of the muscles at the "local" lead:1 - the capacity of the propulsion unit; 2 - the potential of muscle fibers (potential fibrillation); 3 - positive generaciony potential; 4 and 5 - polyphase potentials (Bahtalo); - rhythmic discharges two propulsion units.


Currently, many authors under the propulsion unit understand set of functionally United muscle fibers, working as one. Almost simultaneous excitation occurs in the muscle fibres motor units leads to the fact that there are fluctuations in capacity, reflecting the excitation of motor units as a whole (the potentials of motor units). To study the potentials of motor units typically use a concentric electrode (Fig. 2, 1). Bipolar electrodes (Fig. 2, 2) significantly distort the initial and final part of the capacity of the propulsion unit.
If "local" lead consider the form, duration and amplitude potential of a certain motor units and the type electromyograms (Fig. 3). The shape of the potential of motor units of two-phase or three phase, mainly expressed negative phase; about 3% of cases occur polyphase potentials. The length of the building motor unit depends on their structure. She, as a rule, more muscle with large motor units and less muscle with fine motor units. For example, in the quadriceps muscle of thigh and the anterior tibial muscle, where there are large motor units, including up to 1500-2000, and sometimes more muscle fibers, the average duration of the potential of motor units in adults is 10-15 milliseconds, and in the muscles of the eye, motor units which have 5-10 muscle fibers,is just 1 3 milliseconds. The length of the building motor units increases with age, for example at the age of 10 years for the anterior tibial muscle she 9.7 MS, for 30 years with 12.3 msec, 60 years of 15.2 MS. The amplitude of oscillations of the potential of motor units require less or more remove the electrode from the active muscle fibers and can reach 3-5 MB, however, the average values are much lower, about 200 mV. In a relaxed muscle action potentials are not registered. At a weak muscles potentials motor units follow each other in the form not strictly rhythm of a number roughly equal to the amplitude of oscillations. For the muscles of the limbs number of digits motor unit in one second equals 5-10 with weak reduction, with an average of 20-30 power reduction and 50-60 under strong reduction. Frequency discharges motor unit in small muscles are usually higher than in the large muscles of the eye 150-200 1 sec).
The increase in the force of muscular contraction occurs as by increasing the frequency of repeated excitations separate propulsion units, and at the expense of the involvement of new motor unit. Changes accordingly type "locally" allotted electromyograms. There are three main types: potentials of individual motor units, mixed and interference. With weak reduction register or potentials of individual motor units (1st type), or the many potentials of motor units, among which you can usually highlight the potentials of individual motor units (2nd type). With an average strength and strong reductions registered interference electromyogram in which it is almost impossible to identify the potentials of individual motor unit (3rd class). About the synchronization of discharges of motor units most closely receive information using multielectrode. According to "local" lead, the degree of synchronization bits motor unit with a weak contractions of the muscles in healthy insignificant; it steadily increases in some lesions of the spinal cord (see below electromyography in the clinic). Data global lead, which allows to study electromyogram with long-term and maximum strength contraction of muscles, indicate a significant increase in healthy synchronization bits propulsion units for fatigue and some modes of operation of the muscles.
Potentials of individual muscle fibers can be registered only when denervation muscles when motor units cease to exist as a functional whole and individual muscle fibers begin to "spontaneously" aroused. This so-called potentials fibrillyatsy, which have a duration of 0.5 - 3 msec and range of 50-200 Macs.
"Global" abstraction allows the study of the fluctuations of the electric potential, resulting in a large amount of muscle tissue, usually containing hundreds of motor unit. As a rule, these potentials reflect the amount of potentials of many motor unit; therefore, electromyogram when "global" the abstraction is often called total, although in some circumstances when "global" lead can register and potentials of individual motor unit. For "global" lead, in addition to skin electrodes, you can apply normal needles; in the experiment using implanted electrodes in the form of a silver plates, filed to the muscle. In most cases, using bipolar or unipolar abstraction by means of surface electrodes. Unipolar way of assignment of work physiology of sport. The clinic currently used almost exclusively bipolar abstraction. Under him, the discharge electrodes are placed at a distance of 1 to 2 cm from each other so that one is above the motor point, and the other distal or both over musculoskeletal point. Usually the discharge electrodes are constantly fixed on the insulating plate. In accordance with requests of clinical electromyography developed a special scheme of inspection healthy subjects and patients (ap. C. Usavich). This scheme provides for the mandatory registration of action potentials symmetric muscles alone, i.e., during the maximum random muscle relaxation, with different samples, leading to involuntary change of muscle tension, and arbitrary dismissals. In healthy subjects, well relaxed muscles or not detected any hesitation potential or identified low-amplitude oscillations, which some authors considered to be a manifestation of a tone of muscles. When the posture-tone and random contractions of the muscles of electromyogram presents irregular fluctuations of different amplitudes, the form and duration. With weak reduction registered in more rare and irregular in the amplitude of the oscillations of the potential, with a strong decrease increase the frequency and amplitude of oscillations. The increase of the amplitude of oscillations increases static electricity shown in Fig. 4. Repetition rate fluctuations may be different in different muscles, and in the same muscle groups in different subjects. The average repetition rate fluctuations at maximum power reduction is 100-150 per 1 sec. The amplitude depends on many conditions: muscle development, status, severity of subcutaneous fat (especially when expressed in obesity) and to a large extent on the choice of electrodes. The amplitude of oscillations at maximum power reduction can reach 4-6 MB. However, usually logged smaller values (Fig. 5). Repetition frequency of oscillations of the potential and the oscillation amplitude change when you change synchronization bits motor unit. The increase in sync when fatigue and some modes of operation of muscles leads to a decrease repetition frequency of vibration and the amplitude increase.

Fig. 4. Electromyogram biceps muscle shoulder at static tension of different power (load).
Fig. 5. Electromyograms recorded at maximum power cuts right (upper curve) and the left (lower curve) superficial flexor (bipolar abstraction skin electrodes area of 0.5 cm2 with distance between the centers of the electrodes 20 mm).

A large number of valuable information about the status of different parts of the musculoskeletal system allows to obtain registration of action potentials muscles with electric stimulation of nerves and muscle fibers. Registration electromyograms during stimulation of the muscle fibers electric shock allowed to determine in norm and pathology of the speed of propagation of an excitation of the muscle fibers, and at the irritation of nerves - the state of neuromuscular transmission, the speed of propagation of an excitation by the motor nerve fibers, and explore mono - and polysynaptic reflexes.
In addition to the General visual assessment, applied and mathematical processing of electromyogram. The more widespread the estimated total area electromyograms per unit of time using integrators and machine processing for holding autocorrelazione and especially cross-correlation analysis.