EFFECTS OF 830 NM CONTINUOUS-WAVE LASER-DIODE IRRADIATION ON MEDIAN NERVE FUNCTION IN NORMAL SUBJECTS

The presence, magnitude, and nature of the effect that low intensity l aser irradiation has on nerve function, growth, and repair constitute a contentious area of research. We have addressed one aspect of this c ontroversy by Systematically examining the influence of 830 nm laser r adiation on median nerve function. In particular, we investigated medi an nerve motor and sensory distal latencies, action potential amplitud es, action potential areas, and conduction velocities as well as dorsa l hand skin temperatures in 33 normal subjects in a double-blinded, ra ndomized controlled study. All subjects received identical treatment: 30 seconds of ''irradiation'' at 10 points over the course of the righ t median nerve (five sites on the forearm and five sites distal to the wrist crease) with either an active (1.2 J/point) or inactive (0 J/po int) 40 mW 830 nm continuous wave IR laser diode. Latencies, conductio n velocities, amplitudes, areas, and skin temperatures were collected bilaterally at a baseline immediately prior to irradiation and at inte rvals of 1, 5, 10, 15, 20, and 30 minutes following treatment. Analysi s of the results reveals that motor and sensory distal latencies were decreased in the treated limbs of the laser-treated group relative to the control group by 3-4% (P <.016 and .046, respectively, rank sum te st). No significant differences in these quantities were found between the limbs within either group. Similarly, no alterations of action po tential amplitudes, action potential areas, forearm conduction velocit ies, or skin temperatures were detected within or between the groups. Thus on the basis of this experiment, percutaneous 830 nm continuous w ave laser irradiation can affect median nerve function, but the effect s are quite limited and appear to be limited to the distal portion of the nerve. (C) 1993 Wiley-Liss, Inc.