Conduction velocity and temporal dispersion of the nerve volleys evoked by air-puff stimulation of the index finger and palm.

Air-puff stimuli were delivered to 5 successive sites (3 cm increments) over the index finger and palm to record propagating sensory nerve action potentials (SNAPs) from surface electrodes over the median nerve at the wrist. SNAPs consisted of a series of individual peaks (N1, P1, P2, N2 and P3) and the corresponding peaks in the records with stimulation at the various locations could be identified. The apparent conduction velocity of the first peak determined from the stimulation point at the finger tip to the wrist was 38 m/sec. With stimulation of the more proximal locations it became even slower. This paradoxical slowing is due to an increasing effect in the calculation of conduction velocity of the utilization time at the receptors for air-puff stimulation at progressively proximal sites. Segmental conduction velocity estimated between adjacent stimulus sites was 10-20 m/sec faster than the distal conduction velocity between the finger tip and the wrist. Within each segment, the conduction velocities of the individual peaks were not significantly different. These findings, together with invariant durations of the negative components (N1 and N2) in the propagating SNAPs along the ascending digital nerves, lead to the conclusion that the separate peaks are not the result of temporal dispersion due to differences in conduction velocity of skin afferents, but are primarily due to a more peripheral receptor mechanism involving variable delays in activation of different classes of mechanoreceptors.