THE RELEVANCE OF PULSE REPETITION RATE AND RADIANT EXPOSURE TO THE NEUROPHYSIOLOGICAL EFFECTS OF LOW-INTENSITY LASER (820 NM PULSED WAVE) IRRADIATION UPON SKIN TEMPERATURE AND ANTIDROMIC CONDUCTION LATENCIES IN THE HUMAN MEDIAN NERVE/

The effects of low-intensity near-infra-red laser irradiation (820 nm; 1.5 and 9.0 J cm(-2); pulsed at 12 Hz, 73 Hz and 5 kHz) upon peripher al neurophysiology and skin temperature were investigated using antidr omic conduction studies in the human median nerve in vivo. Healthy hum an volunteers (n = 90) were recruited and allocated randomly to either a control group (n = 10) or one of eight experimental groups (two rad iant exposures, 1.5 J cm(-2) and 9.0 J cm(-2) at one of three pulse re petition rates, 12 Hz, 73 Hz or 5 kHz, in addition to a placebo group for each radiant exposure; n = 10 all groups). Analysis of variance (A NOVA) demonstrated a significant (p less than or equal to 0.05) decrea se in skin temperature following irradiation at the lowest radiant exp osure (1.5 J cm(-2)) combined with pulse repetition rates of 73 Hz and 5 kHz, with the greatest effect at 73 Hz. These changes in skin tempe rature were coupled with increases in negative peak latency (NPL); ie changes in NPL were inversely related to changes in skin temperature. However, in contrast to the authors' previous findings using continuou s wave (CW) laser irradiation, differences in NPL were not found to be significant. These findings, therefore, provide little evidence of th e neurophysiological effects of low-intensity infra-red irradiation at the dosage levels and pulse repetition rates used here.