Frequency sweep electromyogram and voluntary effort in volunteers after d-tubocurarine.

A new method for monitoring the effect of muscle relaxants on the myoneural junction was tested in unanesthetized volunteers. Evoked electromyographic responses to stimulation, sweeping exponentially from 1 to 100 Hz over 10 seconds, were recorded from the hand and abdominal muscles. d-Tubocurarine (dTc) was given intravenously in incremental doses until head lift was abolished. Thumb twitch tension, vital capacity, peak expiratory flow, maximal inspiratory force, and hand grip strength were recorded during partial paralysis and recovery. The frequency sweep electromyogram (FS-EMG) of the musculus rectus abdominis was more depressed than the FS-EMG of the musculus abductor digiti V at the time head lift was abolished. The abdominal muscle recovered faster from dTc paralysis than did the hand muscle. The latter failed to respond normally to the highest frequencies of stimulation during the entire period of observation lasting 72 minutes after dTc injection. At the time of maximal neuromuscular blockade, respiratory function showed less depression than the FS-EMG of the abdominal muscle.