Motor fibre refractory period and motor conduction velocity range.

The absolute and relative motor refractory periods and the range of motor conduction velocity were investigated in 25 normal subjects and in 25 patients suffering from peripheral neuropathy. The refractory periods were examined by a collision method, which eliminates the effect of the first of the paired stimuli, thus allowing the effect of the second stimulus to be clearly recorded. The range of conduction velocity was also examined by a collision method, and the conduction times were corrected by subtracting the absolute and relative refractory periods from the figures given by this method. The maximum motor conduction velocities obtained with this technique closely corresponded with those found using conventional methods. The results show that the refactory periods are prolonged and the conduction velocities are reduced in peripheral neuropathies, especially of segmental demyelination type, but the range of conduction velocity is not necessarily increased. The failure to suppress fully the effect of the proximal stimulus by a distal stimulus is a phenomenon found in peripheral neuropathies.