Demographic characteristics: Total study participants.

<p>^a p≤0.05—nonsmokers vs. ex-smokers</p><p>^b p≤0.05—nonsmokers vs. active smoker</p><p>^c p≤0.05—ex-smokers vs. active smokers</p><p>^# GOLD classification is as detailed in the Global Initiative for Chronic Obstructive Lung Disease [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0134209#pone.0134209.ref024" target="_blank">24</a>].</p><p>Data are expressed as mean±SEM.