A) Disease activity and vagus nerve activity. Disease activity was measured using DAS-28. Note that disease activity is independent of HF power. Kruskal-Wallis ANOVA = 16.72, P = 0.0008; B) Relationship between HMGB1 serum levels and disease activity. HMGB1 serum levels were compared with disease activity scores (DAS-28). Below 3.2 represents low activity, a score of 3.2–5.1 represents intermediate activity, and > 5.1 represents high disease activity. Kruskal-Wallis ANOVA = 13.14 P = 0.004.