A non-invasive computerized measurement of motor neurone refractory period and subnormal conduction in man

A computer-assisted method is described which allows the non-invasive measurement of excitability and conduction velocity during the relative refractory period of alpha motor fibres in peripheral nerves. The method is based on a collision technique combined with a correlation analysis of the compound muscle potential. Using this procedure, the recovery in excitability and conduction velocity succeeding the absolute refractory period was measured in 13 normal subjects. In all subjects a period of subnormal conduction followed by a period of supernormal conduction was observed. The first fibres recovered at a mean of 0.75 +/- 0.07 msec; the last fibres recovered 1.3 +/- 0.3 msec. The period of subnormal conduction for a 100 mm conditioned conduction path length had a mean of 1.87 msec. When the period of subnormal conduction was plotted as a function of the conditioned nerve section, a linear section was observed. Stimulus intensity influenced the recovery in excitability but not the subnormal period. Temperature was found to affect both the excitability and subnormal period.