Maximal mid-expiratory flow detects early lung disease in α₁-antitrypsin deficiency

Pathological studies suggest that loss of small airways precedes airflow obstruction and emphysema in chronic obstructive pulmonary disease (COPD). Not all α₁-antitrypsin deficiency (AATD) patients develop COPD, and measures of small airways function might be able to detect those at risk.Maximal mid-expiratory flow (MMEF), forced expiratory volume in 1 s (FEV₁), ratio of FEV₁/forced vital capacity (FVC), health status, presence of emphysema (computed tomography (CT) densitometry) and subsequent decline in FEV₁ were assessed in 196 AATD patients.FEV₁/FVC, FEV₁ % predicted and lung densitometry related to MMEF % pred (r²=0.778, p<0.0001; r²=0.787, p<0.0001; r²=0.594, p<0.0001, respectively) in a curvilinear fashion. Patients could be divided into those with normal FEV₁/FVC and MMEF (group 1), normal FEV₁/FVC and reduced MMEF (group 2) and those with spirometrically defined COPD (group 3). Patients in group 2 had worse health status than group 1 (median total St George's Respiratory Questionnaire (SGRQ) 23.15 (interquartile range (IQR) 7.09-39.63) versus 9.67 (IQR 1.83-22.35); p=0.006) and had a greater subsequent decline in FEV₁ (median change in FEV₁ -1.09% pred per year (IQR -1.91-0.04% pred per year) versus -0.04% pred per year (IQR -0.67-0.03% pred per year); p=0.007).A reduction in MMEF is an early feature of lung disease in AATD and is associated with impaired health status and a faster decline in FEV₁.