Frequency sweep analysis of neuromuscular junction continuity.

A new technique for measuring neuromuscular junction continuity is described. Junctional transmission is evaluated by integration of the electromyographic (EMG) response induced by intramuscular electrical stimulation. The unique characteristics of this monitoring technique are the use of intramuscular stimulation and a varying stimulation rate. The stimulus frequency is made to increase exponentially from 1 to 100 pulses per second over a period of 10 or 15 seconds. Thin coiled wire electrodes are used for stimulation and recording of the EMG response. The frequency sweep electromyogram (FS-EMB) response was measured in uncurarized and curarized tibialis anterior muscle of cat. In the uncurarized preparation, the FS-EMG response was only slightly decreased with an increasing stimulus frequency. During neuromuscular blockade with d-tubocurarine the FS-EMG response diminished with increasing frequency. The response failed at successively lower frequencies during deeper levels of neuromuscular block. Recovery proceeded in the reverse order. The frequency sweep technique provides quantitative assessment of neuromuscular junction continuity over a broad spectrum of driving frequencies without inducing fatigue. This method does not require force measurements nor voluntary effort. Intramuscular stimulation minimises painful stimuli thus making the frequency sweep technique suitable for evaluating neuromuscular transmission in either conscious or unconscious individuals.