Figure 3. (A) Thermal pain thresholds (means) in injured areas. Dotted lines = legs with sympathetic block; solid lines = placebo-blocked legs. Time -0.75 h indicates observation after block but before injury. The response from each participant was summarized in the mean value of measurements during effective block. Comparison revealed no difference between sympathetic block and placebo (P = 0.23 using Student's t test; n = 16). (B) Mechanical pain thresholds (medians) in injured areas. Von Frey hair numbers 3–8 represent a rank scale, where 3 indicates a force of about 20 mN and 8 about 133 mN. The steps from 3 to 8 are logarithmic increases in force. The response from each participant was summarized in the mean value of measurements during effective block. Comparison revealed no difference between sympathetic block and placebo (P = 0.25 using Student's t test; n = 16). (C) Pain responses (visual analog scale, 0–100; medians) to heat stimuli (41 degrees C, 43 degrees C, and 45 degrees C lasting 5 s) in injured areas. Comparison revealed no differences between sympathetic block and placebo (P values are shown in Figure 3(C); Student's t test; n = 16). (D) Area of secondary hyperalgesia (medians); that is, the area of hyperalgesia to von Frey pinprick (314 mN) around the heat-injured areas. The response from each participant was summarized in the mean value of measurements during effective block. Comparison revealed no difference between sympathetic block and placebo (P = 0.50 using Student's t test; n = 16).