Conduction velocities of Adelta-fibers and C-fibers in human peripheral nerves and spinal cord after CO2 laser stimulation.

Conduction velocities (CVs) in two nociceptive afferents were estimated to clarify the mechanism of pain transmission. Late and ultra-late laser evoked potentials (LEPs) were recorded by stimulating Adelta- and C-nociceptive nerve endings at different skin sites (the hand, foot, and skin overlying the 7th cervical and 12th thoracic vertebrae), by which data CVs of the arm (CVA), leg (CVL), and spinothalamic tract (CVSTT) were estimated. In late LEPs, Adelta-CVA and Adelta-CVL respectively were between 6.7 and 23.7 (mean +/- SD, 12.8 +/- 5.2) m/s, and 9.0 and 26.7 (17.2 +/- 5.6) m/s. Adelta-CVSTT was between 4.1 and 22.1 m/s (10.6 +/- 5.8). In ultra-late LEPs, C-CVA and C-CVL respectively varied between 1.0 and 2.1 (mean +/- SD, 1.5 +/- 0.3) m/s, and 1.0 and 1.9 (1.4 +/- 0.2) m/s. C-CVSTT was between 1.0 and 3.9 (1.8 +/- 0.8) m/s. No significant difference was found among CVA, CVL, and CVSTT values calculated from late or ultra-late LEP latencies. Nociceptive signals of the primary Adelta- and C-afferents therefore may be conveyed separately by myelinated (Adelta-) and unmyelinated (C) axons through peripheral nerves and spinal cord.