Patients in this cohort who have GOLD stage @ to @ ( post-bronchodilator FEV@/FVC < @ and FEV@ < @ % of predicted ) , who receive reimbursement by health insurance companies for physical therapy ( post-bronchodilator Tiffeneau-index < @ ) and who experience a COPD exacerbation will be asked within @ days to participate in a cohort-nested prospective randomised controlled trial ( RCT ) .