Hyperalgesia in a human model of acute inflammatory pain: a methodological study

The aim of the study was to examine reproducibility of primary and secondary hyperalgesia in a psychophysical model of human inflammatory pain. Mild burns were produced on the crura of 12 volunteers with a 50×25 mm thermode (47°C, 7 min). Assessments of (i) cold and warm detection thresholds, (ii) mechanical and heat pain thresholds, (iii) pain to heat (43°C and 45°C, 5 s), (iv) secondary hyperalgesia, and (v) skin erythema were made 1.75 and 0.5 h before, and 0, 1, 2, 4, and 6 h after a burn injury. Sensory thresholds and hyperalgesia to heat and mechanical stimuli were examined by contact thermodes and von Frey hairs, and pain intensity was rated with a visual analog scale (0–100). To describe between-day reproducibility, the subjects were examined three times at intervals of 21 days. Within-day comparisons showed that a 20% change could be detected as significant for all variables with fewer than 12 subjects in a cross-over design (2 α=5% and power=80%). Between-day comparisons demanded up to 25 subjects to detect changes of the same magnitude. The burns caused mild to moderate pain (VAS: mean 29, SD 14) and the subjects (all right-handed) were more sensitive to heat pain on their left side ( P