Individual variability in vasoconstrictive tone with thermal stimulation. (A) Top signal represents thermode temperature; next 2 signals depict microvascular blood flow in the finger of 2 representative subjects. Subject 1 shows vasoconstriction during each cycle of 4 thermal pulses, with good recovery of blood flow to baseline between cycles (Pre-CD, Pre-HD, Pre-HP, and Pre-CP). Subject 2 shows vasoconstriction during each cycle of thermal pulses, with poor recovery of blood flow between stimuli and progressive decrease in flow. (B) Linear slopes depicting microvascular blood flow between thermal stimuli (Pre-CD, Pre-HD, Pre-HP, and Pre-CP) for controls and patients with SCD subjects. The patients (red) showed poor recovery with a progressive decrease in blood flow between thermal stimuli compared with controls (blue) who mostly showed good recovery of the blood flow to baseline between thermal stimuli. (C) The mean recovery slope for SCD and control individuals (Student t test of mean slope values, P = .042). CD, cold detection; CP, cold pain; HD, heat detection; HP, heat pain.