What are the implications of a relatively low Forced Expiratory Volume in one second (FEV1) to Forced Vital Capacity (FVC) ratio in interstitial lung disease?

From the Guidelines

A relatively low FEV1/FVC ratio in interstitial lung disease (ILD) indicates an obstructive component alongside the restrictive pattern, necessitating comprehensive evaluation and treatment addressing both aspects. This mixed pattern can be seen in conditions such as combined pulmonary fibrosis and emphysema syndrome, rheumatoid arthritis-associated ILD, or when ILD coexists with asthma or COPD 1. The diagnosis of an obstructive defect is primarily based on a low FEV1/VC ratio, which is a critical parameter for identifying obstructive impairment and predicting morbidity and mortality in patients with respiratory diseases 1.

Key Considerations

• The FEV1/VC ratio is the most important parameter for identifying an obstructive impairment, and a low ratio, even with a normal FEV1, predicts morbidity and mortality 1.
• A reduced VC does not necessarily prove a restrictive pulmonary defect; it may be suggestive of lung restriction when FEV1/VC is normal or increased 1.
• Treatment should include anti-inflammatory or antifibrotic medications for the interstitial disease, such as prednisone, mycophenolate mofetil, or nintedanib, and bronchodilators like tiotropium or a combination LABA/ICS for the obstructive component.
• Oxygen supplementation is crucial if resting or exertional hypoxemia is present.
• Pulmonology referral is essential for a definitive diagnosis and personalized treatment planning, as the approach depends on the exact underlying condition causing this mixed physiologic pattern.

Diagnostic Approach

• Complete pulmonary function tests, including measurement of lung volumes, are necessary for confirming airway obstruction and assessing lung hyperinflation 1.
• High-resolution CT imaging of the chest is vital for evaluating the extent and distribution of interstitial lung disease and any coexisting conditions like emphysema.
• The use of additional parameters such as peak expiratory flow (PEF) and maximum inspiratory flows may assist in diagnosing extrathoracic airway obstruction 1.

From the FDA Drug Label

The FDA drug label does not answer the question.

From the Research

Interstitial Lung Disease and FEV1/FVC Ratio

• Interstitial lung disease (ILD) is a group of pulmonary disorders characterized by inflammation and/or fibrosis of the lung parenchyma, which can lead to progressive dyspnea and end-stage respiratory failure 2.
• The diagnosis of ILD typically involves a multidisciplinary approach, including key history and examination features, blood panel, pulmonary function tests, high-resolution computed tomography imaging, and when required, bronchoalveolar lavage and lung biopsy results 3.
• A relatively low FEV1/FVC ratio is not typically associated with ILD, as ILD is characterized by a restrictive ventilatory defect, whereas a low FEV1/FVC ratio is indicative of an obstructive pattern 4.

FEV1/FVC Ratio in ILD

• However, a study found that high expiratory flows, including a high FEV1/FVC ratio, can be an early abnormality in patients with ILD, particularly in those with normal forced vital capacity (FVC), total lung capacity (TLC), and carbon monoxide diffusing capacity (Dlco) 5.
• In this study, high FEV1/FVC was the most common abnormality in patients with ILD, including those with idiopathic pulmonary fibrosis (IPF), and could allow for earlier diagnosis and treatment 5.

Comparison with Other Studies

• Another study found that using the lower limit of normal (LLN) of the FEV1/FVC ratio to define airflow obstruction can affect the classification and outcomes of patients with chronic obstructive pulmonary disease (COPD) 6.
• However, this study did not specifically address the FEV1/FVC ratio in patients with ILD, and its findings may not be directly applicable to this population.

Clinical Implications

• The findings of these studies suggest that a relatively low FEV1/FVC ratio may not be a typical feature of ILD, but a high FEV1/FVC ratio can be an early abnormality in some patients with ILD 5.
• Further research is needed to fully understand the clinical implications of the FEV1/FVC ratio in patients with ILD and to determine its utility as a diagnostic or prognostic tool 2, 3, 5.