Figure 4From: Predictors of exacerbation frequency in chronic obstructive pulmonary diseaseChange in FEV 1 . FEV1(A) in patients experiencing infrequent (Group 1) and frequent exacerbations (Group 2, including Group 2A and Group 2B) and (B) and those experiencing mildly frequent exacerbations (Group 2A) and severely frequent exacerbations (Groups 2B) over time.Back to article page