We postulated that low-power laser irradiation could produce analgesia, nerv ous activation, and enhancement of wound healing in association with changes in the microcirculation. In order to confirm this hypothesis, we monitored blood flow in rats be fore and after laser treatment. A Ga-Al-As semiconductor laser (wave length: 810nm) was used. Rats were treated at either (1) 300mW×3min, (2) 500mW×3min, (3) 700mW×3min, (4) 300mW×20min, (5) 500mW×20min, or (6) 700mW×20min. Blood flow was monitored in the dorsal skin before and after irradiation using a Laser-Doppler flowmeter. The peripheral circu lation was improved by 20min of irradiation with a 300mW or 500mW semiconductor laser without any irreversible tissue damage, and it was inferred that tissue restoration would result from this change. Different responses were produced depending on the irradiation condi tions, and this suggested that there is a safe range between transition from non effective to effective and from effective to irreversible damage. This range was considered to be the saf est and most effective for low-power laser treatment.
