Role of volume-conductor properties of muscles in the formation of evoked contractions during stimulating electrical impedance myography.

Experiments on the preparation of frog sartorius muscle showed that electrical impedance myogram of evoked muscle contractions is the sum of electric processes accompanying contraction of some muscle fibers or muscle regions. Inverted muscle response probably results from heterotopic excitation of distant muscle regions under conditions of reduced excitability of muscle fibers adjacent to the electrode. During centrifugal propagation of contractions, especially in altered muscles, the negative wave on the myogram corresponding to impedance decrease is sometimes followed by a positive wave. The possibility for recording of heterotopic contractions indicates that the impedance of the electrode-muscle interface produces no considerable effects on the shape of electrical impedance myogram. These results hold much promise for the diagnostics of neuromuscular diseases.

Effect of early fasciotomy on intramuscular pressure and electrical excitability of muscles in experimental compartment syndrome.

Experiments on rabbits with compartment syndrome of the leg showed that the main pathogenetic factors of muscle injury are postischemic contracture leading to extravascular microcirculatory disorders and tissue necrosis(early postcompression period) and progressive subfascial edema (18 h-4 days). Therapeutic effect of fasciotomy in the early period consists in restoration of bloodflow due to relaxation of contracted muscles and in the late period in decompression of edematous muscles and prevention of secondary ischemia. Fasciotomy through a small section does not lead to sufficient relaxation of rigid muscles and does not essentially increase the subfascial volume. Fasciotomy decreases subfascial pressure and muscle excitability threshold, however they remain considerably elevated during day 1. An electrodiagnostic test is proposed for early (before subfascial edema) detection of postischemic contracture.

New relationship between electrical characteristics of evoked contractions in skeletal muscles during necrobiosis.

Evoked muscle contractions at different stages of necrobiosis were investigated by stimulating impedance myography in patients with vascular pathology and acute or chronic ischemic syndrome of the lower extremities. The threshold and maximum amplitudes and current strength for contraction responses were determined, and the dependence of evoked contractions on stimulating current was evaluated. Approximation of the obtained curves with the well-known force-time excitation curves demonstrated the relationship between excitability and contractility parameters depending on the stage of ischemic necrobiosis. This regularity is a more universal interrelation between muscle electrical characteristics. Electrical characteristics of evoked contractions depend on various factors influencing muscle structure and function.

[Study of contractile properties of muscles of curarized animals by the method of stimulation impedancography]. / Issledovanie sokratitel'nykh svoistv myshts kurarizirovannykh zhivotnykh metodom stimuliatsionnoi impedansografii.

The effect of relaxation doses of tubocurarine on the stimulation and contractile properties of muscles in complete synaptic block was studied in experiments on laboratory rats by means of a previously developed method of stimulation impedancography. During intramuscular electrostimulation the stimulus threshold for short 0.01 mc test impulses increased, while the steepness of the characteristic "force of action--contractile effect" curve, registered at 1 mc impulses, reduced. The reduction was caused by loss of the function of synaptic nerve structures which take part in recruiting the contractile elements. Nonsynaptic mechanisms of recruiting through direct stimulation of the muscle fibres ensure 45% of recruitment. Changes of the duration of the contraction were not detected in the first 20 minutes of the effect. After 60-80 minutes of relaxation there was a tendency to prolongation of the time of the contraction act, which may be caused by prolonged immobilization of the animals.

[Method for electrodiagnosis of the necrotic zone in skeletal muscles]. / Sposob élektrodiagnostiki zony nekroza skeletnykh myshts.

A simple new method for determination of necrosis of the skeletal muscles is suggested. Stimulation of the muscle and the recording of the contraction is made via a needle electrode. The contraction is recorded as a characteristic drop of the muscle resistance to high-frequency current which per se does not cause any stimulation. The zone of necrosis does not demonstrate any characteristic changes in the resistance. The presence of necrosis in the areas under exploration was proved histologically.