CHARACTERIZATION OF THE RELATIONSHIP BETWEEN MOTOR END-PLATE JITTER AND THE SAFETY FACTOR

A mathematical model developed for a personal computer was used to sim ulate the jitter phenomenon in neuromuscular transmission in order to characterize the relationship between jitter and the safety factor. Fo ur models of normal and abnormal neuromuscular transmission were inves tigated. In a human experiment, the mean consecutive difference (MCD) values for stimulated single-fiber electromyography at firing rates of 1, 2, 5, and 10 Hz were measured in 137 motor end-plates of myastheni c patients. Results of the computer simulations show that the relation ship between jitter and the safety factor is exponential like. Variati ons in jitter are most prominent in end-plates with low safety factors . This relationship agrees with results of human end-plate studies. Ch anges in the MCD values caused by presynaptic depression or facilitati on are linearly correlated to the initial jitter, whereas the logarith mic values of MCD are not. It is very important to keep in mind this n onlinear relationship when relating single-fiber jitter to the safety factor. (C) 1998 John Wiley & Sons, Inc.