Dependence of refractory period measurements on conduction distance: a computer simulation analysis

Computer simulations were used to study the recovery of conduction velocity in the temporal and spatial domains during the relative refractory period. The impulse exhibits increased duration and reduced amplitude during the relative refractory period as well as a reduced conduction velocity. Changes in conduction velocity are reflected by a deviation from linearity in the plots of latency variation versus interstimulus interval and of interval-between-impulses versus intersimulus interval. The latency increase for the second impulse is monotonically related to interstimulus interval, and is maximal at the beginning of relative refractory period. The magnitude of the latency increase is also related monotonically, but not in a linear manner, to conduction distance. The distance-dependence of latency variation during the relative refractory period is most marked close to the site of impulse initiation. These findings may be relevant to relative refractory period measurements in clinical neurophysiology.