A Low Forced Expiratory Flow of 25% to 75% May Indicate Early COPD

Among patients with forced expiratory flow between 25% and 75% of vital capacity, a lower FEF was associated with greater airway limitation.

Forced expiratory flow between 25% and 75% of vital capacity (FEF25-75) is likely to identify patients with early evidence of pathologic lung damage in need of careful monitoring and early intervention to prevent additional lung injury, according to study findings published in BMJ Open Respiratory Research.

Traditional spirometric parameters — including forced expiratory volume in 1 second (FEV1), forced vital capacity (FVC), and FEV1/FVC — are critical to diagnosing and gauging the severity of chronic obstructive pulmonary disease (COPD).  Researchers therefore sought to establish the prevalence of low FEF25-75 among individuals with a history of smoking (referred to as “ever-smokers” by study authors), including those with and without airflow limitation (AL). The investigators also sought to determine whether FEF25-75 is associated with the severity of AL.

The researchers conducted a retrospective, cross-sectional analysis based on anonymized data from patients with known or suspected COPD. All participants had undergone routine pulmonary function testing at University Hospitals Birmingham National Health Service Foundation Trust, United Kingdom, with data collected between January 1, 2016, and April 30, 2021. Study inclusion criteria were: (1) symptoms suggestive of COPD (ie, breathlessness and/or a persistent cough); (2) at least 30 years of age; (3) smoking history of at least 10 pack-years; (4) COPD confirmed or suspected by a senior physician; and (5) complete reporting of all traditional spirometric parameters, including FEF25-75.

A total of 1457 ever-smokers were classified into 1 of 3 groups, based on predefined criteria: (1) those with normal FEF25-75/no AL (n=316); (2) those with low FEF25-75/no AL (n=335); and (3) those with low FEF25-75/AL (n=806).

The analysis showed that the low FEF25-75 was observed in 99.9% of individuals with AL and in 50% of those without AL. Participants in the low FEF25-75/no AL group had lower spirometric parameters than did those in the normal FEF25-75/no AL group. FEF25-75 was shown to decrease with the severity of AL.

Participants in the low FEF25-75/AL group demonstrated significantly lower lung function (P <.001 for all comparisons) than did those in the low FEF25-75/no AL group and those in the normal FEF25-75/no AL group.

Based on a logistic regression model, in the absence of AL, the presence of low FEF25-75 was linked to lower FEV1 and FEV1/FVC — even when smoking history was taken into consideration.

Several limitations of the present study should be noted. Because this was a retrospective study, available data were limited to routine lung function tests, which is more representative of the real-world approach to such strategies. Further, although studies have shown that that residual volume (RV)/total lung capacity (TLC) is also a potential marker for small airway function, the data evaluated in this study were restricted to spirometric parameters and did not include lung volumes such as RV and TLC.

The authors concluded that “FEF25-75 is part of routine lung function assessment, and therefore, closely monitoring patients with low FEF25-75 and considering early interventions may be central to improving health and prognosis.”