The double collision technique: a new method for measurement of the motor nerve refractory period distribution in man.

A new, double collision, technique is described for non-invasive measurement of the motor nerve refractory period distribution for human peripheral nerves. In contrast to previous collision techniques, this method is independent of the transient changes in nerve and muscle fibre conduction which can distort test muscle responses. The end-point of the distribution is determined by a null response; this permits accurate identification of those nerve fibres with the longest refractory periods. We have used the double collision technique to measure the refractory period distributions for the median nerve at the wrist in 20 normal subjects aged between 22 and 58 (mean 35) years. 150% maximal stimuli were used with a controlled limb temperature of 35 degrees C. Following a conditioning stimulus, the mean latencies for recovery of 5%, 50%, 95% and 99% of motor nerve fibres were 0.94, 1.03, 1.12 and 1.23 msec respectively. Data are also presented for the ulnar and peroneal nerves. The results show that the human motor nerve refractory period distribution is much less dispersed than has been previously supposed.