Effect of ischaemia on the potentials of human single muscle fibres.

The changes in the parameters of the extracellular potentials of single muscle fibres are studied during ischaemia. These changes have two phases, preceded in part of the cases by a transient phase. The decrease in the propagation velocity (V) of the excitation predominates in the first phase, therefore, the length of the depolarized area (b) is shortened. The shortening of b, directly demonstrated by VEMG, conditions an increase in the peak-to-peak amplitude of the potentials (Ap) and of its components: the amplitude of the initial positive phase (A1) and the amplitude of the negative phase (Ad). During the second phase there is predominance of the lengthening of the time for depolarization (TD), as well as the time for fast repolarization (TR). This is manifested in elongation of the times for increase and decrease of the negative phase, accompanied by an increase in the times for increase and for decrease of the initial positive phase. The increase in b, proved directly by the changes in VEMG, results from the longer TDR. The increase in b leads to a decrease in the amplitudes Ap, AI and Ad. The changes during ischaemia are analogous to a certain extent to the changes in continuous activity of the muscle fibre, but the former occur more rapidly. They are accompanied by changes in the AI/Ad ratio which suggests changes in the intracellular potentials, most probably changes in the after-potentials. During ischaemia the influence of hypoxy is summated probably with the influence of long-lasting discharge and lowered temperature of the muscle.