Increased expiratory flows identify early interstitial lung disease.

Background: Most interstitial lung diseases (ILDs) manifest with a restrictive ventilatory defect as the common physiologic abnormality. Low carbon monoxide diffusing capacity (Dlco) is considered to be the earliest abnormality on pulmonary function tests (PFTs) in patients with ILD. However, its measurement requires complex and expensive equipment. Our study aimed to assess if high expiratory flows are the earliest PFT abnormality in patients with idiopathic pulmonary fibrosis (IPF) and ILD.

Methods: In a real-world cohort of incident cases with ILD, we identified the initial PFTs on all patients newly diagnosed with ILD at Kingston Health Sciences Center (in Kingston, Ontario, Canada) between 2013 and 2017. The diagnosis of ILD, including IPF, was established as per current guidelines. Among patients with normal forced vital capacity (FVC), total lung capacity (TLC), and Dlco, we assessed the frequency of high expiratory flows defined as forced expiratory volume in 1 s (FEV₁)/FVC, FEF₂₅, FEF_25-75, FEF_75, and peak expiratory flow > 95% confidence limit of normal. We adjusted for emphysema, increased airway resistance, and obesity.

Results: We assessed PFTs of 289 patients with ILD; 88 (30%) of them had normal FVC, TLC, and Dlco. Among these, high FEV1/FVC was the most common abnormality in 37% of patients, in 43% of nonobese patients, and in 58% of those with no emphysema and normal airway resistance. Results were similar in the 88 patients with IPF.

Conclusions: High FEV1/FVC could allow identifying patients with ILD/IPF in the earliest stages of their disease with simple spirometry, leading to earlier diagnosis and treatment.