Stimulating Aδ and C-Fibers in the Lower Limb With a 980 nm Diode Laser

2013 Journal of Neurology Research  
Laser evoked potentials are increasingly used to investigate the integrity of the nociceptive system. Laser heat stimuli can activate Aδ fibers, activation of C-fibers remains difficult. This study attempts to stimulate Aδ and C fibers separately with a 'grid' to generate respectively late and ultra-late LEPs. A 'grid' is a thin aluminum plate used as a spatial filter to stimulate C-fibers. Furthermore, study subjects pressed a button upon detecting a laser stimulus which was used to measure
more » ... ction times (RT) following diode laser stimulation. Methods: Cutaneous heat stimuli were applied at the Th 12 and L 5 dermatome in seventeen volunteers. Conduction velocities (CV) were calculated by measuring latencies of P2 and reaction times (RT). Results: Stimulation condition Th 12 no-grid showed a P2 late response at 330 ± 47 ms and L 5 no-grid at 413 ± 53 ms. Mean reaction time during Th 12 no-grid was 537 ± 146 ms, L 5 no-grid 784 ± 334 ms, Th 12 grid 710 ± 195 ms and L 5 grid 1,391 ± 336 ms. During stimulation block Th 12 grid and L 5 grid ultra-late LEPS could not reliably be generated. Median conduction velocities (CV) and their corresponding range were calculated. The median CV RT no grid was 5.8 m/s (range 1.2 -43.3). The median CV LEP no grid was 13.8 m/s (range 4.7 -45.4). The median CV RT grid was 1.9 m/s (range 0.8 -3.7). Ultra-late LEPs could not be generated, although subjects mentioned a long lasting burning pain during Th 12 grid and L 5 grid . Conclusions: This study questions the feasibility of the 'grid' to reliably generate C-fiber responses. Pressing a button upon laser stimulus detection seems preferable for identifying C-fiber stimulation in the lower limb, whereas for Aδ nociceptive pathways laser evoked potentials might be of use.
doi:10.4021/jnr177w fatcat:fwuf7yqlbbajde5uisasqtpcvq