Measurement of skin temperature after infrared laser stimulation

OBJECTIVES Several types of lasers are available for eliciting laser evoked responses (LEPs). In order to understand advantages and drawbacks of each one, and to use it properly, it is important that the pattern of skin heating is known and duly considered. This study was aimed at assessing the skin temperature during and immediately after irradiation with pulses by Nd:YAP and CO(2) lasers. MATERIALS AND METHODS The back of the non-dominant hand was irradiated in 8 subjects. Temperatures were measured by a fast analogical pyrometer (5 ms response time). Stimuli were tested on natural colour (white) and blackened skin. RESULTS Nd:YAP pulses yielded temperatures that were correlated with pulse energy, but not with pulse duration; much higher temperatures were obtained irradiating blackened skin than white skin (ranges 100-194 degrees C vs 35-46 degrees C). Temperature decay was extremely slow in white skin, reaching its basal value in more than 30 s. CO(2) pulses delivered with power of 3W and 6W yielded temperatures of 69-87 degrees C on white skin, and 138-226 degrees C on blackened skin. Temperature decay was very fast (4-8 ms). CONCLUSIONS Differences in peak temperatures and decay times between lasers and tested conditions depend on energy and volume of heated skin. The highest temperatures are reached with lesser degree of penetration, as in the case of CO(2) laser and blackened skin. Taking into account the temperature decay time of the skin, the minimum interstimulus interval to get reliable LEPs should be no less than 10 s for Nd:YAP and 100 ms for CO(2) laser. Another important practical consequence of the heating pattern is that the Nd:YAP pulses will activate warmth receptors more easily than CO(2).

[1]  R. Treede,et al.  CO2 laser radiant heat pulses activate C nociceptors in man , 1983, Pflügers Archiv.

[2]  R. LaMotte,et al.  Comparison of responses of warm and nociceptive C-fiber afferents in monkey with human judgments of thermal pain. , 1978, Journal of neurophysiology.

[3]  A. D. Towell,et al.  CO2 laser activation of nociceptive and non-nociceptive thermal afferents from hairy and glabrous skin , 1996, Pain.

[4]  L. Arendt-Nielsen,et al.  Sensory and pain threshold characteristics to laser stimuli. , 1988, Journal of neurology, neurosurgery, and psychiatry.

[5]  Andrew C. N. Chen,et al.  Lasers and other thermal stimulators for activation of skin nociceptors in humans , 2003, Neurophysiologie Clinique/Clinical Neurophysiology.

[6]  J. Lefaucheur,et al.  Clinical application of laser evoked potentials using the Nd:YAG laser , 2002, Neurophysiologie Clinique/Clinical Neurophysiology.

[7]  Gian Domenico Iannetti,et al.  Laser guns and hot plates , 2005, Pain.

[8]  I. Tracey,et al.  Aδ nociceptor response to laser stimuli: selective effect of stimulus duration on skin temperature, brain potentials and pain perception , 2004, Clinical Neurophysiology.

[9]  R. Haimi-Cohen,et al.  A model for the temperature distribution in skin noxiously stimulated by a brief pulse of CO2 laser radiation , 1983, Journal of Neuroscience Methods.

[10]  R. Treede,et al.  Nerve fibre discharges, cerebral potentials and sensations induced by CO2 laser stimulation. , 1984, Human neurobiology.

[11]  J. Lorenz,et al.  Neurophysiological evaluation of pain. , 1998, Electroencephalography and clinical neurophysiology.

[12]  A. Mouraux,et al.  How do we selectively activate skin nociceptors with a high power infrared laser? Physiology and biophysics of laser stimulation , 2003, Neurophysiologie Clinique/Clinical Neurophysiology.

[13]  G. M. Hale,et al.  Optical Constants of Water in the 200-nm to 200-microm Wavelength Region. , 1973, Applied optics.

[14]  J. Lefaucheur,et al.  Laser evoked potentials using the Nd:YAG laser , 2001, Muscle & nerve.

[15]  B. Bromm.  Modern techniques to measure pain in healthy man. , 1985, Methods and findings in experimental and clinical pharmacology.

[16]  U. Baumgärtner,et al.  Clinical usefulness of laser-evoked potentials , 2003, Neurophysiologie Clinique/Clinical Neurophysiology.

[17]  A standardized electrode for percutaneous recording of A and C fibre units in conscious man. , 1981, Acta physiologica Scandinavica.

[18]  R. Meyer,et al.  Evidence for two different heat transduction mechanisms in nociceptive primary afferents innervating monkey skin. , 1995, The Journal of physiology.

[19]  Walter Magerl,et al.  C- and Aδ-fiber components of heat-evoked cerebral potentials in healthy human subjects , 1999, Pain.