Monochromatic infrared irradiation (890 nm): effect of a multisource array upon conduction in the human median nerve.
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).


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).


CONCLUSIONS
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.
Noble
J G
JG
Rehabilitation Sciences Research Group, University of Ulster at Jordanstown, Newtownabbey, Northern Ireland.
Lowe
A S
AS
Baxter
G D
GD
D000328:Adult; D000704:Analysis of Variance; D004307:Dose-Response Relationship, Radiation; D005260:Female; D006801:Humans; D007259:Infrared Rays; D008297:Male; D008475:Median Nerve / Q000502:physiology / Q000528:radiation effects*; D009431:Neural Conduction / Q000502:physiology / Q000528:radiation effects*; D011336:Probability; D011829:Radiation Dosage; D011930:Reaction Time / Q000528:radiation effects; D012016:Reference Values; D012680:Sensitivity and Specificity