Abstract
Chronic obstructive pulmonary disease (COPD) is diagnosed and its severity graded by traditional spirometric parameters (forced expiratory volume in 1 s (FEV
)/forced vital capacity (FVC) and FEV
, respectively) but these parameters are considered insensitive for identifying early pathology. Measures of small airway function, including forced expiratory flow between 25% and 75% of vital capacity (FEF
), may be more valuable in the earliest phases of COPD. This study aimed to determine the prevalence of low FEF
in ever-smokers with and without airflow limitation (AL) and to determine whether FEF
relates to AL severity.
A retrospective analysis of lung function data of 1458 ever-smokers suspected clinically of having COPD. Low FEF
was defined by z-score<-0.8345 and AL was defined by FEV
/FVC z-scores<-1.645. The severity of AL was evaluated using FEV
z-scores. Participants were placed into three groups: normal FEF
/ no AL (normal FEF
/AL-); low FEF
/ no AL (low FEF
/AL-) and low FEF
/ AL (low FEF
/AL+).
Low FEF
was present in 99.9% of patients with AL, and 50% of those without AL. Patients in the low FEF
/AL- group had lower spirometric measures (including FEV
FEF
/FVC and FEV
/FVC) than those in the normal FEF
/AL- group. FEF
decreased with AL severity. A logistic regression model demonstrated that in the absence of AL, the presence of low FEF
was associated with lower FEV
and FEV
/FVC even when smoking history was accounted for.
Low FEF
is a physiological trait in patients with conventional spirometric AL and likely reflects early evidence of impairment in the small airways when spirometry is within the 'normal range'. FEF
likely identifies a group of patients with early evidence of pathological lung damage who warrant careful monitoring and reinforced early intervention to abrogate further lung injury.