Chronic Obstructive Pulmonary Disease (COPD), even due to α-1-antitrypsin deficiency (A1AD), is recognised as having distinct radiological, physiological and clinical phenotypes. Little is known about disease progression in physiologically defined phenotypes.1 We have identified a subgroup of patients with a reduced FEV1 but normal gas transfer determined by the lower limit of normal (LLN), that is, with standardised residual (SR) value <−1.645. The current abstract reports the progression of these physiological measures with time in this subgroup.
Methods 533 patients with A1AD were studied of whom 43 had isolated FEV1 abnormality at baseline and also had ≥3 years of complete annual follow-up data. These patients were followed for a mean of 5.9 (2.2 SD) years. Of these, 22 remained with isolated FEV1 abnormality (Group A) whereas 21 had developed evidence of a reduced K,co deficiency (Group B). Group A and B data at baseline and at last follow-up were compared—see Abstract S64 Table 1.
Results There were no differences in FEV1, smoking, age or sex distribution between the groups. At baseline mean K,co SR was worse in Group B compared to Group A. However, Group A had significantly worse total Saint George's Respiratory questionnaire score (SGRQ) at baseline. K,co SR significantly deteriorated in both groups during follow-up (p<0.001 in both cases) but this was not true for FEV1 SR. Group B had a significantly faster decline in K,co than Group A (p=0.005) resulting in all values falling below the LLN.
Conclusion About half of the A1AD patients with an isolated FEV1 abnormality at baseline have a decline in K,co faster than expected. Whether exacerbations, treatment or emphysema distribution relates to faster decline remains to be determined.