Monochromatic Infrared Irradiation (890 nm): Effect of a Multisource Array upon Conduction in the Human Median Nerve

Abstract

Objective: Antidromic conduction studies in the human median nerve were used to assess the neurophysiological effects of irradiation of the skin overlying the nerve using a novel treatment unit comprising a multisource monochromatic infrared diode array (Equilight, Denver, CO). Materials and Methods: Healthy human volunteers (n = 40) were recruited and randomly allocated to one of four groups: control, placebo, or one of two treatment groups (1.7 and 4.0 J/cm²). After baseline recordings of negative peak latency (NPL) were completed on the nondominant arm, subjects were treated according to group allocation. Recordings were subsequently repeated at 5-min intervals over a 45-min period. Results: Analysis of negative peak latency difference scores (ANOVA) demonstrated significant differences in NPL between groups and over time (p < 0.05). While in the control and placebo groups NPL values remained relatively stable, in the two treatment groups such values decreased marginally, with the greatest effects observed in the 4.0 J/cm² group (e.g., at 5 min, differences in NPL [mean ± SEM]: control group, 0.02 ± 0.03 msec; treatment group 2, 4 J/cm², -0.07± 0.03 msec). Similar significant differences were observed in skin temperature; correlation analysis indicated a weak (but expected) positive linear relationship between skin temperature and nerve conduction velocity (r = 0.125). Conclusion: These results suggest that irradiation at the parameters and under the conditions used here produce a direct neurophysiological effect. The magnitude of such effects are in keeping with previous findings using single source arrays at higher radiant exposures or thermal effects of the treatment unit.