IL6 and chronic obstructive pulmonary disease: Such interrelation has recently been suggested by Chhabra and colleagues, who recently showed a positive correlation between serum IL-6 and the low frequency (0.04–0.15 Hz)/high frequency (0.15–0.40) component ratio of heart rate variability (LF/HF ratio), a marker of sympathetic activation, in patients with COPD (although such an interpretation needs to be made with caution) (Chhabra et al., 2015).