Hashimoto I, Yoshikawa K, Sasaki M, Gatayama T, Nomura M
Department of Neurosurgery, Tokyo Metropolitan Hospital of Fuchu, Japan.
Electroencephalogr Clin Neurophysiol. 1989 Apr;72(4):321-33. doi: 10.1016/0013-4694(89)90068-0.
Brief air-puff stimuli were applied to the tip of the index finger to record propagating sensory nerve action potentials (APs) from pairs of surface electrodes at successive sites over the median nerve of the distal forearm. Within 10 msec, air-puff stimulation elicited 2-4 separate waves lasting 3-6 msec, in contrast to a single triphasic wave evoked by electrical stimulation. Amplitudes of air-puff evoked APs were much smaller than those of electrically induced APs. However, the amplitude ratio of the initial negative wave (P1-N1) of electrically evoked APs to that of air-puff induced APs declined linearly as a function of recording points along the ascending median nerve. Similarly, the duration ratio of the same component (N1) increased progressively in the proximal direction along the nerve. These results suggest that air-puff evoked afferent volleys undergo considerably less temporal dispersion than those induced by electrical stimulation. Thus, each peak of air-puff evoked APs represents a relatively homogeneous afferent fiber population. The initial P1, N1 and P2 peaks of air-puff evoked APs occurred later than those of electrical induced APs, and the latency included the time of skin indentation and receptor transduction in response to mechanical stimulation. Proximal conduction velocities were faster than distal conduction velocities due to cancellation of the extra delay at the skin mechanoreceptors as well as a true increase in the proximal direction. There were no significant differences between the interelectrode conduction velocities of the fastest fibers activated by the air-puffs and by electrical stimulation. Interelectrode propagation velocities of the different peaks from the same segments had no significant differences for air-puff evoked APs. The presence of multiple peaks may not be the result of temporal dispersion due to difference in conduction velocity of skin afferents but primarily due to a more peripheral receptor mechanism involving transduction and impulse generation.
