MEASUREMENTS OF ARGON-LASER LIGHT ATTENUATION IN THE SKIN INVIVO USING A UNIQUE ANIMAL-MODEL

A dorsal skin flap chamber model for microcirculation studies permits direct irradiation of subcutaneous arterioles and venules ‘in vivo’ as well as irradiation of the same vessels through the skin of unanaesthetized hamsters. A system has been developed to permit vital and video microscopy while selected vessels of the microvascular system are being irradiated. Information relating to light attenuation in the skin can be obtained by comparing the response curves of irradiation aimed directly to the blood vessels to those of laser light delivered to vessels through the skin. Selected vessels have been irradiated with the argon laser (488 nm and 514.5 nm) adjusting the power to deliver radiant exposures 1 to 55 J cm−2 on a 250 μm diameter spot during a 20 ms irradiation time and embolized or stationary coaguli are produced in response to the irradiation. The radiant exposure threshold for production of embolized coaguli when irradiation is directed at the surface of the skin is 1.45 times larger than the threshold when the vessel is directly irradiated. The skin to vessel threshold ratio for the production of stationary coaguli is 1.39. Higher doses are required through the skin because of light attenuation due to absorption and scattering. These ratios are compared with the predictions of two light distribution models based on Beer's law and the Monte Carlo solution of the radiative transfer equation. © 1992, Baillière Tindall. All rights reserved.