STIMULUS FREQUENCY IN THE DETECTION OF NEUROMUSCULAR BLOCK IN HUMANS

Study of the literature on the physiology of neuromuscular transmission suggested two new methods of assessing the degree of neuromuscular block in the human subject. These were, first, a comparison of the height of the recorded twitch tensions developed in response to repeated single stimuli applied at differing frequencies and, second, examination of the extent of reduction in amplitude of twitch tensions developed in response to a short train of four stimuli. In assessing the first method the use of three frequencies of stimulation was tried (i.e., 0.1 Hz (c.p.s.), 0.3 Hz and 1.0 Hz). It was found that as the frequency of stimulation was increased there was reduction in the amplitude of the recorded twitch response in curarized subjects, and that this reduction appeared to depend on the degree of curarization. In assessing the second method a short train of four stimuli at 2 Hz was used, and it was found that there was a progressive fade of successive recorded mechanical twitch responses in curarized subjects which again appeared to depend on the degree of curarization. It is suggested that the amplitude of the twitch response at a higher frequency expressed as a percentage of that at the slower rate, and the last response of the train of four expressed as a percentage of the first may be useful in measuring degree of neuromuscular block in man.