Fig. 1From: High-dose N-acetylcysteine for long-term, regular treatment of early-stage chronic obstructive pulmonary disease (GOLD I–II): study protocol for a multicenter, double-blinded, parallel-group, randomized controlled trial in ChinaClinical trial design. COPD, chronic obstructive pulmonary disease; CAT, COPD assessment test; CCQ, COPD clinical questionnaire; mMRC, modified British Medical Research Council dyspnea scaleBack to article page