Cold-evoked pain varies with skin type and cooling rate, a psychophysical study in humans

grantor: University of TorontoThis thesis examined the effect of skin type and cooling rate on the intensity, quality and time-course of cold-evoked pain in normal human subjects. Cold stimuli were delivered to the thenar eminence (glabrous skin) and the dorso-lateral hand (hairy skin) via a 9cm$\sp2$ Peltier-type stimulator. Cold and pain thresholds were determined by the method of limits. A computerized visual analogue scale was used to obtain continuous ratings of pain intensity and affect. The McGill Pain Questionnaire was used to assess the quality of cold-evoked pain. Supra-threshold stimuli (34$\sp\circ$C base) were delivered at 0.5, 1 or 2$\sp\circ$C/s to 2$\sp\circ$C, held for 20s and returned to baseline at 9$\sp\circ$C/s. These studies revealed: (1) Cold and cold-induced pain thresholds were lower (e.g. occurred at a higher temperature) for hairy compared to glabrous skin. (2) Power function exponents for supra-threshold ratings were larger for glabrous skin than for hairy skin. (3) Pain indices were higher for slower cooling rates. (4) No differences were found for pain ratings of intensity and affect. (5) Cold-evoked painful paradoxical heat sensations occurred most often during innocuous cooling.M.Sc