Canadian journal of anaesthesia = Journal canadien d'anesthésie
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Shortly after elicitation of a muscle response by supramaximal stimulation of its motor nerve, there exists a period of refractoriness of neuromuscular transmission when a second stimulation elicits only a submaximal response or no response at all. Many anaesthetics and neuromuscular blocking and facilitatory drugs change the refractoriness of neuromuscular transmission. ⋯ Based on an existing technique of digitization and time expansion of the neurally evoked compound electromyogram (ncEMG), we developed a computer programme of waveform subtraction, and determined in nine normal awake volunteers the various interstimulus intervals when neuromuscular transmission was refractory (RP0), 3/4 refractory (RP.25), half refractory (RP.5), 1/4 refractory (RP.75) or non-refractory (RP1). We confirmed our hypotheses that computer-based waveform subtraction of the digitized ncEMG is a feasible and necessary technique for the accurate determination of the RPs of neuromuscular transmission, and report that the normal values in humans are: RP0 = 1.0 +/- 0.1, RP.25 = 1.3 +/- 0.3, RP.5 = 1.9 +/- 0.3, RP.75 = 2.9 +/- 0.5, and RP1 = 6.6 +/- 1.9 ms (mean +/- SD), respectively, in the ulnar nerve-first dorsal interosseous muscle model.