A method to measure the cutaneous thermal threshold by means of a CO2 laser

The purpose of this study is to determine the cutaneous warm perception threshold in normal subjects. This study is performed at different environmental conditions. A CO2 laser and a system of lenses and mirrors have been used for letting infrared radiation of various intensity values I impinge onto a surface S of 1 cm(2) of the forearm volar surface of the dominant limb. The times t(s) and the radiation intensities I-s corresponding to the warm sensation threshold have been recorded. A model has been implemented assuming that the radiation is completely absorbed in the first layers of the skin, where the thermal receptors are located. This model agrees with the experimental results, and allows the evaluation of the threshold energy ET adsorbed into the receptor layer necessary to reach the cutaneous warm sensation. This energy corresponds to the limit of the product I-s . t(s) . S as t(s) tends to zero.