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Significant FEV1 responsiveness in patients with different grade of COPD. Significant responsiveness was assessed using ATS-ERS criterion based on FEV1 and FEV1 percentage predicted criterion in patients with different grade of COPD. The connected slash represents the responsive ratios of the two criteria across all the grades of COPD. **, P<0.01, compared with ATS-ERS criterion based on FEV1; ***, P<0.001, compared with ATS-ERS criterion based on FEV1.
