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.

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.

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.