Figure 1. The α and β diversity assessment of gut microbiota. (A) The α diversity was evaluated by observed OTUs, Chao1, Shannon and Simpson indexes. The β diversity was evaluated by (B) PCA, (C) PCoA and (D) NMDS. H: healthy controls; COPD: Chronic obstructive pulmonary disease; PCA: Principal Component Analysis; PCoA; Principal coordinate analysis; NMDS: Non-metric multidimensional scaling.