Box plots of SP-A concentrations among healthy subjects and COPD patients according to stage.

<p>Panel (A) shows SP-A mass concentration (pg/L) and panel (B) shows SP-A weight percent (wt%). Healthy subjects (n = 11) and patients with COPD stage 2 (n = 2), stage 3 (n = 5) and stage 4 (n = 6) were included. Horizontal lines represent the median, diamond shapes represent the mean, boxes represent the interquartile range and whiskers represent the range.