Airflow obstruction is a key characteristic of asthma and is objectively measured using spirometry, a pulmonary function test. This obstruction is defined by a reduction in the FEV1/FVC ratio. FEV1, or forced expiratory volume in one second, represents the volume of air forcefully exhaled in the first second of exhalation. FVC, or forced vital capacity, is the total volume of air that can be forcefully exhaled after a full inhalation. In obstructive lung diseases like asthma, FEV1 is disproportionately reduced compared to FVC. Conversely, in restrictive lung diseases, both FEV1 and FVC are reduced proportionally, resulting in a relatively preserved FEV1/FVC ratio.
The FEV1 component is often more responsive to bronchodilator treatment in obstructive conditions. Therefore, assessing reversibility of airflow obstruction is crucial in asthma diagnosis and management. Reversibility is typically defined by a significant increase in FEV1 after bronchodilator administration. The established criteria for significant bronchodilator reversibility, according to the American Thoracic Society (ATS) and the European Respiratory Society (ERS), is an increase of 12% or more from baseline in either FEV1 or FVC, accompanied by an absolute increase of at least 200 mL in either parameter.
While FEV1 is the primary focus in assessing bronchodilator response in asthma, changes in FVC can also be clinically relevant. Although historically less emphasized than FEV1 in asthma, FVC reversibility can occur and has been studied, particularly in the context of severe Chronic Obstructive Pulmonary Disease (COPD) where hyperinflation is prominent. Some research indicates that in severe COPD, the FVC response to bronchodilators may be more pronounced than the FEV1 response. However, it’s important to note that this observation is more frequently associated with COPD and less so with asthma.
To provide definitive guidance on the criteria for reversibility in asthma, we consulted with Dr. Tom Casale, a leading expert in the field. Dr. Casale directed us to the Global Initiative for Asthma (GINA) guidelines, the internationally recognized standard for asthma management. The GINA criteria clearly define reversibility of airflow obstruction in asthma as an increase in FEV1 of 12% or greater, and at least 200 mL.
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Alt text: GINA guidelines flowchart illustrating asthma diagnosis criteria, emphasizing FEV1 reversibility testing and FEV1/FVC ratio assessment in adults and children for confirming airflow limitation in asthma.
In conclusion, the FEV1/FVC ratio is a fundamental measurement in diagnosing airflow obstruction in asthma. Bronchodilator reversibility, indicated by a significant improvement in FEV1 (≥12% and ≥200 mL), remains a cornerstone in confirming asthma diagnosis. While FVC changes can occur, particularly in other obstructive diseases like severe COPD, FEV1 remains the more reliable and primary parameter for assessing bronchodilator response and reversibility in asthma. Understanding the FEV1/FVC ratio and reversibility criteria is essential for accurate asthma diagnosis and effective patient management.
References
- Girard WM, Light RW. Should the FVC be considered in evaluating response to bronchodilator. Chest 1983;84:87-89.
- Saad, Helmi Ben, et al. “The forgotten message from gold: FVC is a primary clinical outcome measure of bronchodilator reversibility in COPD.” Pulmonary pharmacology & therapeutics 21.5 (2008): 767-773.
- Pellegrino R, Viegi G, et al. Interpretative strategies for lung function tests. Eur Respir J 2005;26:948-968.
- Newton MF, O’Donnell DE, Forkert L. Response of lung volumes to inhaled salbutamol in a large population of patients with severe hyperinflation. Chest 2002;121:1042-50.
