Fig. 4
Human diode laser induced heat pain depends on TRPV1-expressing nerve fibers. a Mean pain thresholds (stimulus duration at 100 mW) on hand and foot (n = 10). After desensitization by 8% capsaicin for 24 h (Qutenza®), laser heat pain sensations were abolished and stimuli were not perceived even at maximum stimulus duration (390 ms) and laser power (100 mW); ***p < 0.001, paired t-test. b, c Psychometric functions (% painful stimuli) before (open symbols) and after (filled symbols) capsaicin (circles) or vehicle patch application (diamonds) for 24 h. T50 values indicated as dotted lines. d–e Pain ratings displayed a linear increase in double logarithmic coordinates following a power function with an exponent of 1.1 at the hand and 1.2 at the foot. Pain perception was completely abolished after TRPV1 desensitization by application of a capsaicin patch for 24 h (filled circles)