BDNF and chronic obstructive pulmonary disease: Although we did not find a significant difference in BDNF serum levels in patients with COPD compared to controls, we observed lower concentrations in the cases with a mean value of 964.1 ± 101.0 (SEM) pg/mL (median of 832.5 pg/mL, range of 190.7–4114.1 pg/mL) and 1094.6 pg/mL ± 194.5 (SEM) pg/mL (median of 845.7 pg/mL, range of 395.2–3637.0 pg/mL) of the control group (p = 0.521, Mann–Whitney U test) (Figure 1A).