ELECTROMYOGRAPHY [electro-(from «electricity») + a miografiya] — the method of a research of a functional condition of skeletal muscles based on registration of the electric biopotentials arising in them.
The electromyography allows to investigate a functional condition of a muscle at various fiziol. and patol. changes and also to obtain information on a state and safety of an innervation at various levels. Besides, E. widely use for studying of various reflex reactions in physiology of motive systems of an organism, in a pathophysiology of the peripheral neuromotor device, in functional diagnosis of diseases of peripheral nerves and muscles, disturbances of neuromuscular transmission, during the studying of labor processes, mechanisms of exhaustion, in a sports, space and air medicine. AA. found also application in anesthesiology for definition of efficiency of muscle relaxants and control of their action.
The beginning of studying of the electric phenomena in muscles is connected with N. E. Vvedensky's works (1884). The first registration of the electromyogram by means of a string galvanometer and its description rapid development of a method and its widespread introduction in a wedge are made by Piper (N. E. of Piper, 1907), however. to the practician are connected with development of the needle electrode which considerably expanded possibilities of use of an electromyography.
Biopotentials of muscles amplify and registered by means of an elektromiograf. The modern elektromiograf represents the difficult device consisting of electrodes for removal of biopotentials of muscles, the intensifying block, an oscilloscope, the photo recorder for record of the electromyogram (EMG) on photographic paper.
Electrodes for removal of biopotentials of muscles are subdivided on superficial (lamellar) and needle. Superficial electrodes, as a rule, make of conducting metal, to-ry shall have anticorrosive property. Usually silver or mix of powders of silver with silver chloride is applied to this purpose. Needle electrodes carry out more often in the form of a thin continuous core to dia. to 0,5 — 0,7 mm.
Range of amplitudes of an elektromiografichesky signal lies ranging from units of microvolts to several tens millivolts. Frequency of following of signals fluctuates ranging from 0,5 Hz to several hundred hertz, but separate components of a range of EMG can have the frequency of 10 — 20 kHz. Sensitivity of modern elektromiograf makes 5 mkv.
The strengthened biopotentials of muscles are displayed on the screen of an oscilloscope. The part of an elektromiograf consisting of the intensifying block and an oscilloscope is called mioskopy. Mioskop has from one up to four intensifying blocks independent from each other that allows to investigate four elektromiografichesky signals at the same time.
In modern elektromiograf, except main units, there are additional devices — a programmable electrostimulator, the EMG integrator, the EMG analyzer, a loud-speaker for listening of a soundtrack. The programmable electrostimulator is used for a research of evoked potentials. The electrostimulator develops impulses of current and tension according to the set program and through electrodes provides their giving on certain body parts. Amplitude, frequency and duration of impulses can be regulated with the broad range. The EMG integrator is used to the information processing concluded on the electromyogram. The EMG analyzer is necessary for allocation of amplitude of separate components of a frequency range of EMG for the subsequent their processing.
Further improvement of elektromiograf goes on the way of automation of management of operation of the device, automation of processing of EMG by means of the micro COMPUTER.
The biopotentials registered in a muscle are generated by muscle fibers (see. Bioelectric potential , Miografiya ). In normal conditions excitement of muscle fibers happens only at receipt of an impulse to them on motive axons. At the same time all muscle fibers innervated by one axon, i.e. which are a part of one motive unit are excited at the same time (see. Muscular contraction ). Potential of separate motive unit can be registered only at any effort. In process of increase in force of reduction an increasing number of motive units is excited and the frequency of their impulsation increases. EMG registered in these conditions represents result of summing of biopotentials of a large number or all motive units of a muscle.
Depending on research objectives E. carry out to time of full relaxation of a muscle (an electromyography of rest), at various degree of its any tension (an electromyography of any effort) or stimulation of a muscle by irritation of the innervating her nerve (studying of the caused electric answers of a muscle).
The electromyography of rest allows to register the electric phenomena occurring in a muscle in the conditions of its full relaxation. Normal at the same time fluctuations of biopotentials do not come to light. At introduction to a muscle of a needle electrode or its subsequent easy movement potentials lasting 1 — 3 ms, with an amplitude up to 100 mkv are registered. In some cases duration of this type of activity can increase considerably, in other cases, e.g. at ischemic necroses, activity of introduction does not come to light.
At introduction of a needle electrode to a zone of an arrangement of trailer plates of synapses "noise of trailer plates" — the repeating negative monophase potentials lasting 0,5 — 2 ms and with an amplitude less than 100 mkv, connected with spontaneous secretion of acetylcholine is registered.
Fibrillation potentials arise in 5 — 14 days after injury of a nerve (depending on localization of damage). These are two-phase or three-phase fluctuations of potential are (more rare) (fig. 1, a) lasting not more than 5 ms, is more often from 1 to 3 ms; their amplitude 30 — 150 mkv. Sometimes are found a potentsia ly fibrillations with an amplitude up to 1100 mkv.
Positive acute waves usually are registered with 15 — the 30th day after denervation of a muscle and can be traced then within several years. On EMG these waves have a characteristic appearance (fig. 1, b). Amplitude and duration of positive acute waves are very variable — respectively from 30 to 500 mkv and from 5 to 30 ms.
The Miotonichesky category (fig. 1, c) — the category of the repeating two-phase potentials, or positive acute waves of high frequency (to 150 in 1 sec.) and the changing amplitude. Due to the change of frequency of fluctuations and amplitudes of the potentials making the category at its listening through a loud-speaker of an elektromiograf the characteristic soundtrack with increase and decrease in tone — «a sound of the diving bomber» is heard.
The category of high frequency, the psevdomiotonichesky category (fig. 1, d) — the repeating emergence of potentials with high frequency (from 20 to 150 in 1 sec.) at an invariance of their amplitude and a form. Sudden emergence and disappearance of this form of activity without the previous change of frequency is characteristic.
Potentials of fastsikulyation (fig. 1, e) are registered in a muscle out of its any reduction and have parameters of potentials of the motive units registered in the same muscle. Essential difference of potentials of fastsikulyation from potentials of motive units is various frequency of their emergence: despite an irregularity of an impulsation the average interval between potentials of fastsikulyation makes 1 — 3 sec., and between potentials of motive units — apprx. 100 ms.
Miotonichesky categories are a characteristic sign myatonias (see). Existence of spontaneous activity of muscle fibers, and also potentials of fastsikulyation in the prevailing most cases demonstrates denervatsionny process, i.e. about the disease connected with defeat of motor-neurons or motive axons. Potentials of fibrillations and positive acute waves come to light at various diseases which are followed by a necrosis of muscle fibers — polymiosites (see. Miositis ) and the progressing muscular dystrophies (see. Myopathy ). Intensity of spontaneous activity is the indicator of sharpness and weight of denervatsionny and necrotic processes in a muscle. At approach of remission or recovery of an innervation it decreases, and at a complete recovery of function of muscle fibers — stops.
From potentials of the fibrillations and fastsikulyation registered at patol. processes, it is necessary to distinguish so-called high-quality fibrillations and fastsikulyation. So, single potentials of fibrillations can be noted in muscles of healthy people. In these cases no more than 1 — 2 fibrillations with the wrong change of frequency at a research come to light not less than 20 points of a muscle. «High-quality» fastsikulyation can be also revealed in a muscle at exhaustion; they match in the parameters potentials of motive units in healthy muscles.
Electromyography of any effort. At weak reduction of a muscle it is possible to track activity of separate motive units, at more intensive reduction of EMG reflects activity of all or considerable number of motive units. For registration and the analysis of potentials of separate motive units use, as a rule, needle electrodes, to-rye enter into thickness of a muscle. Total electric activity of a muscle can be revealed both by means of needle, and by means of superficial electrodes. The form, amplitude and duration of potentials of motive units depend on type of the pickup electrode, its arrangement but to the relation to muscle fibers of this motive unit and a zone of trailer plates.
The potentials of motive units registered in muscles of healthy people have two-three phases. At introduction of an electrode to a zone of trailer plates of a synapse (see. Synapse ) the first phase of potential has a negative initial deviation (fig. 2, a). At an arrangement elek a troda out of a zone of trailer plates an initial deviation — positive (fig. 2, b). The main part of potential of motive unit — Spike (action potential) — forms at the expense of summation of potentials of the muscle fibers located closer to the taking-away surface of an electrode. Slow parts of potential form at the expense of summation of potentials of separate fibers of this motive unit.
As duration of separate potentials of motive units in muscles of healthy people fluctuates in quite considerable limits, a measure of their assessment is the average duration of potentials of motive units. This size is rather stable in various muscles at persons of a certain age. It is average arithmetic duration not less than 20 potentials of the motive units registered in a muscle during the movement of the pickup electrode in four various directions from the place of its introduction and immersion on various depth. Increase in average duration of potential of motive unit is result, as a rule, of inclusion in structure of motive units of new muscle fibers and bigger dispersion of fibers of this motive unit in the studied muscle that is a consequence of the compensatory innervation (spruting) which is carried out by the remained axons at denervatsionny processes. Shortening of duration of potential of motive unit is characteristic of primary muscular frustration (a myopathy, the progressing muscular dystrophy, a polymiositis), and also can be observed at early stages of denervatsionny process at nek-ry forms of neuropathies. Change of average duration of potential of motive unit is preceded by change of duration of the separate potentials of motive units making it and their distribution in muscles.
By means of developed by Ekstedt (1964) special electrodes for registration of potentials of separate muscle fibers it is possible to investigate density of muscle fibers in motive unit. At various denervatsionno-reinnervatsionny processes as a result of a compensatory innervation the size of average density of muscle fibers reaches higher values but to comparison with norm.
Inclusion in the existing elektromiografichesky installations of averagers allowed to study parameters of the potentials generated practically by all or the majority of muscle fibers of this motive unit by introduction to a muscle of a needle electrode with the big taking-away surface. This method received in literature the name «macroelectromyography», and the registered potentials — «macropotentials of motive units». At the diseases which are followed by reinnervation increase in amplitude of macropotentials of motive units is observed, at primary damages of muscles — its reduction.
The interferential electromyogram is result of summing of potentials of all motive units participating in performance of this tension of a muscle and being in a zone of assignment of electrodes. During the use of standard plate electrodes with the taking-away surface of 30 — 60 mm2 located at distance in 1 — 2 cm from each other in the conditions of the maximum tension of a muscle of the healthy person the average amplitude of fluctuations of potentials of EMG makes 800 mkv, and frequency — 100 — 200 in 1 sec.
At secondary, or denervatsionny, frustration when the number of the functioning motive units decreases, the frequency of impulses decreases by EMG of the best any effort, and amplitude of fluctuations of potentials increases. At severe damages of a muscle the rare oscillations reflecting activity of a small number of motive units are registered. At primary diseases of muscles, on the contrary, reduction of amplitude of fluctuations of potentials of EMG and increase in frequency of impulses is noted.
The caused electric answers of a muscle. At indirect stimulation of a muscle is registered several fluctuations of its potential. One IS them is the M-answer, to-ry reflects excitement of muscle fibers owing to distribution of an excitation wave on motor axons of a nerve to a muscle. Amplitude of the M-answer depends on the number of the axons excited at stimulation of a nerve. At the current exceeding for 50% current, the M-answer, necessary for obtaining the maximum values (the supramaksimalny mode of stimulation, supramaksimalny current) all axons and respectively all motive units of this muscle are stimulated. Amplitude of the answer testifies to number of innervated fibers in a muscle, and its correct two-phase form — of a sinkhropnost of carrying out excitement on separate axons. Decrease or uvelicheshyu amplitudes of the answer at repeated inspection demonstrates reduction or increase in number of innervated fibers.
Definition of rate of propagation of excitement is based on comparison of a difference of latent times of the M-answer (i.e. time between applied irritations on a nerve and an initial deviation of potential of a muscle from the isoline) at stimulation of a nerve in two or more points located more proksimalno and more distally. Having defined distance between points, in to-rykh stimulation of a nerve was carried out, and the difference in duration of stages of latency can be determined the rate of propagation of excitement (RPE) by a formula: SRV = P / (LVP - LVD); where P — distance between points of stimulation of a nerve in meters, LVP and LVD — duration of stage of latency in seconds, at stimulation of a nerve respectively in more proximal and in more distal point.
Speed spread of activation to a large extent depends on the age inspected. Due to the processes of myelination of motive axons happening at the child in the first years of life and increase in their diameter rate of propagation of excitement increases to 3-5-year age approximately twice, and then continues to increase slowly, reaching a maximum by 14 — 15 years. Rate of propagation of excitement depends also on temperature of the fabrics surrounding a nerve. Reduction or temperature increase of an extremity on 1 ° changes this indicator to 1,2 — 2,4 m/s. Therefore at its research temperature of skin shall be not lower than 32 °. At lower temperature of skin warming of an extremity is necessary. At t ° 32 ° rate of propagation of excitement on elbow and median nerves makes 50 — 80 m/s, to fibular and tibial nerves — 40 — 60 m/s.
Rate of propagation of excitement in proximal sites of nerves is slightly higher, than in distal. It is caused by reduction of diameter of axons and distances between Ranvye's interceptions in distal sites of a nerve. The relation of rate of propagation of excitement in proximal sites of a nerve to this indicator in distal sites (proximal and distal coefficient) at healthy people makes 1,03 — 1,2. At diseases of motive axons changes of parameters of the M-answer and rate of propagation of excitement are observed. The most essential changes are noted at the neuropathies which are followed by demyelination (see. Demyelinating diseases ), In these cases increase in rate of propagation of excitement, and also change of a form of the M-answer — emergence of several peaks, its prolixity is characteristic. At defeat of axial cylinders (aksonopatiya) rate of propagation of excitement can remain within normal amounts for a long time in connection with safety of the carrying-out function of the separate quickly carrying out axons while amplitude of the M-answer sharply decreases. Perhaps local change of speed spread of activation in a zone of a compression of a nerve at so-called tunnel neuropathies that has essential value for their diagnosis (see. Tunnel syndromes ).
Change of amplitude of the M-answer at indirect stimulation of a muscle supramaksimalny current is widely used for a research of neuromuscular transmission. At healthy people at stimulation with a frequency of 3 impulses of 1 sec. amplitude of the M-answer does not change. At stimulation of muscles in the same conditions, but at patients with defeats of synapses, e.g. with myasthenia (see) and various myasthenic syndromes, the decrease in amplitude of the subsequent answers with a maximum to the 5th answer reflecting switching off of a certain number of muscle fibers (myasthenic reaction) is noted. At myatonias (see) there is a long strong reduction and slow relaxation — miotonichesky reaction. Criterion of weight of synoptic frustration is the relation of amplitude of the fifth to the first M-answer as a percentage. This phenomenon reflects only extent of decrease in reliability of neuromuscular transmission. It is offered several functional trials promoting identification of its subclinical disturbances. Treat them: stimulation with a frequency of 3 impulses in 1 sec. after the maximum any muscle tension (post-activation exhaustion), after a tetanization of a muscle (post-tetanic exhaustion), stimulation against the background of ischemia. Introduction of a prozerin and other aktikholinesterazny drugs at a myasthenia and nek-ry myasthenic syndromes reduces extent of decrease in amplitude at stimulation of a muscle rare impulses.
Change of amplitude of the M-answer at indirect stimulation of a muscle with a frequency of 50 impulses in 1 sec. is used in a wedge. conditions for studying of a condition of system of secretion and resynthesis of acetylcholine. At healthy people of stimulation in these conditions does not lead to considerable changes of the M-answer, but at a myasthenia reduction of its amplitude is quite often noted. At change of function of the neuromuscular transmission connected with disturbance of secretion of acetylcholine (at a myasthenic syndrome like Eaton — Lambert and botulism), the low amplitude of the M-answer and the progressing increase of its amplitude (a phenomenon of a vrabatyvaniye) rogistirutsya.
Bibliography: Gokht B. M. and Ilyin N. A. Neuromuscular diseases. page 22. M. 1982; Gekht B. M. in Kasatkin of L. F. Tipologiya of potentials of motive units and density of muscle fibers at neuromuscular diseases. Zhurn. neuropath. and penkhiat., t. 84, No. 11. 6. 1635, 1981.
B. M. Gekht; Yu. Ya. Gavrikov (tekhn.).