Spatial temperature distribution in human hairy and glabrous skin after infrared CO2 laser radiation

Abstract

BackgroundCO2 lasers have been used for several decades as an experimental non-touching pain stimulator. The laser energy is absorbed by the water content in the most superficial layers of the skin. The deeper located nociceptors are activated by passive conduction of heat from superficial to deeper skin layers.MethodsIn the current study, a 2D axial finite element model was developed and validated to describe the spatial temperature distribution in the skin after infrared CO2 laser stimulation. The geometry of the model was based on high resolution ultrasound scans. The simulations were compared to the subjective pain intensity ratings from 16 subjects and to the surface skin temperature distributions measured by an infrared camera.ResultsThe stimulations were sensed significantly slower and less intense in glabrous skin than they were in hairy skin (MANOVA, p < 0.001). The model simulations of superficial temperature correlated with the measured skin surface temperature (r > 0.90, p < 0.001). Of the 16 subjects tested; eight subjects reported pricking pain in the hairy skin following a stimulus of 0.6 J/cm2 (5 W, 0.12 s, d1/e2 = 11.4 mm) only two reported pain to glabrous skin stimulation using the same stimulus intensity. The temperature at the epidermal-dermal junction (depth 50 μm in hairy and depth 133 μm in glabrous skin) was estimated to 46°C for hairy skin stimulation and 39°C for glabrous skin stimulation.ConclusionsAs compared to previous one dimensional heat distribution models, the current two dimensional model provides new possibilities for detailed studies regarding CO2 laser stimulation intensity, temperature levels and nociceptor activation.

Temporal and spatial temperature distribution in the glabrous skin of rats induced by short-pulse CO2 laser

“…2), which was also used in a human study, 11 to represent the skin of the rat's paw. However, the simulation results were not satisfactory (see Sec.…”

“…24 and 25) (K is the absolute temperature). The other parameters were set according to Frahm et al 11 The temperature distribution was based on Pennes's bioheat Fig. 1 Experimental protocols.…”

“…Current knowledge is based on a longer pulse duration (hundreds of milliseconds) in human data. 11,12 Currently, the precise distributions of short-pulse lasers are highly dependent on 1-D mathematic modeling with experimental validation 13 or rely on 1-D 14 or three-dimensional (3-D) 15 mathematic modeling without experimental validation.…”

Human Experimental Pain Models for Assessing the Therapeutic Efficacy of Analgesic Drugs

“…Laser. Light amplification by stimulated emission of radiation (i.e., LASER) is a special light source possessing the ability to evoke heat pain and are applied to the skin by noncontact radiation pulses emitted by CO 2 lasers, thulium lasers, or diode lasers (Plaghki and Mouraux, 2003;Frahm et al, 2010). A␦ fibers (mean conduction velocity, 14 m/s) and C fibers (0.8 m/s) are activated simultaneously, and the perceived pain is described as "pricking" (Bromm and Treede, 1991).…”

“…An advantage is that lasers deliver large amounts of energy to the skin in a highly reproducible manner and are therefore efficient and temporally well controlled heat stimulators that are useful for quantitative sensory testing and recording of time-locked evoked brain potentials (Plaghki and Mouraux, 2003;Frahm et al, 2010). Another advantage is that the stimulus can be applied without direct contact to the skin, providing a purely thermal stimulation (Staahl and Drewes, 2004;Tzabazis et al, 2011).…”