A paradoxical action of minute doses of nondepolarizing muscle relaxants in anaesthetized man.

The administration of minute doses of all currently available nondepolarizing muscle relaxants result in an increase in contractile force of the skeletal muscles. This surprising finding has been obtained by means of mechanograms of the hand muscles after electrical stimulation of the ulnar nerve (100-200 volts, 0.3 msec, 0.2 Hz). Higher doses produce a decrease in contractile force and a paralysis of the skiltalmuscles. The paradoxical action of muscle relaxants can be explained by repetitive firing of the muscle action potential as has been demonstrated in the phrenic nerve-diaphragm preparation with tubocurarine and gallamine.