From the Guidelines
A relatively low FEV1/FVC ratio indicates airflow obstruction, which is characteristic of obstructive lung diseases like asthma, chronic obstructive pulmonary disease (COPD), or bronchiectasis, and according to the most recent guidelines, a post-bronchodilator FEV1/FVC ratio <0.7 is diagnostic of airways obstruction 1. This ratio represents the proportion of air forcefully exhaled in the first second (FEV1) compared to the total lung capacity that can be exhaled (FVC). Normal values are typically above 0.70-0.75, with lower values suggesting obstruction. If you have a low ratio, you should consult a pulmonologist for proper evaluation, which may include additional pulmonary function tests, chest imaging, and assessment of symptoms. Treatment depends on the underlying cause but often includes bronchodilators like albuterol (90-180 mcg, 2 puffs every 4-6 hours as needed) or long-acting medications such as tiotropium (18 mcg once daily) for COPD, or inhaled corticosteroids like fluticasone (100-500 mcg twice daily) for asthma. Lifestyle modifications are also important, including smoking cessation, regular exercise within tolerance, and avoiding respiratory irritants. The severity of obstruction, determined by how low the FEV1/FVC ratio is and the absolute FEV1 value, guides treatment intensity and the need for combination therapies, with the Global Initiative for Chronic Obstructive Lung Disease (GOLD) providing a classification system for COPD severity based on post-bronchodilator FEV1 percentage predicted and FEV1/FVC ratio 1. Key points to consider in managing a patient with a relatively low FEV1/FVC ratio include:
- Using pre-bronchodilator spirometry to rule out COPD and post-bronchodilator measurements to confirm the diagnosis, as recommended by the GOLD Science Committee 1
- Considering the potential for "volume responders" who may have a normal pre-bronchodilator FEV1/FVC ratio but a low post-bronchodilator ratio due to gas trapping and increased residual volume
- Monitoring patients with discordant results longitudinally to assess for changes in lung function and symptoms
- Emphasizing the importance of lifestyle modifications, including smoking cessation and regular exercise, in addition to pharmacological treatment.
From the FDA Drug Label
The precise function of these receptors, however, is not yet established. Studies in asthmatic patients have shown that less than 20% of a single albuterol dose was absorbed following either IPPB (intermittent positive-pressure breathing) or nebulizer administration; the remaining amount was recovered from the nebulizer and apparatus and expired air. There was a significant dose-related response in FEV1 (forced expiratory volume in one second) and peak flow rate. In controlled clinical trials, most patients exhibited an onset of improvement in pulmonary function within 5 minutes as determined by FEV1. FEV1 measurements also showed that the maximum average improvement in pulmonary function usually occurred at approximately 1 hour following inhalation of 2. 5 mg of albuterol by compressor-nebulizer and remained close to peak for 2 hours.
The FEV1/FVC ratio is not directly addressed in the provided drug label. However, FEV1 is mentioned as a measure of pulmonary function that shows significant improvement after albuterol administration.
- A relatively low FEV1/FVC ratio may indicate obstructive lung disease, but this is not explicitly stated in the label.
- The label does discuss the effects of albuterol on FEV1 and peak flow rate, but does not provide information on how to interpret a relatively low FEV1/FVC ratio 2.
From the Research
Definition of Low FEV1/FVC Ratio
A low FEV1/FVC ratio is defined as a postbronchodilator forced expiratory volume in 1 second to forced vital capacity (FEV1/FVC) ratio of 0.7 or less, which is diagnostic in a patient with dyspnea, chronic cough or sputum production, and a history of irritant exposure 3.
Classification of COPD Severity
The severity of chronic obstructive pulmonary disease (COPD) can be classified using the FEV1/FVC ratio, with a new severity classification scheme (STaging of Airflow obstruction by Ratio; STAR) providing discrimination for mortality that is similar to the GOLD classification but with a more uniform gradation of disease severity 4.
Diagnostic Criteria
The diagnostic criteria for COPD include a low FEV1/FVC ratio, with a fixed ratio of 0.7 or less, or a ratio below the age-dependent lower limit of normal (LLN) derived from general population data 5.
Grading of Obstructive Ventilatory Defect (OVD)
An OVD can be graded using the FEV1/FVC ratio, with a low ratio indicating an obstructive defect, and the severity of the defect classified as mild, moderate, moderately severe, severe, or very severe 6.
Interpretation of Pulmonary Function Tests
Pulmonary function tests, including spirometry, can be used to diagnose and manage respiratory problems, with a low FEV1/FVC ratio indicating an obstructive defect, and the severity of the defect determined by the FEV1 (percentage of predicted) 7.
Key Points
- A low FEV1/FVC ratio is diagnostic of COPD in patients with dyspnea, chronic cough or sputum production, and a history of irritant exposure.
- The severity of COPD can be classified using the FEV1/FVC ratio.
- The diagnostic criteria for COPD include a low FEV1/FVC ratio, with a fixed ratio of 0.7 or less, or a ratio below the age-dependent lower limit of normal (LLN) derived from general population data.
- An OVD can be graded using the FEV1/FVC ratio, with a low ratio indicating an obstructive defect.
- Pulmonary function tests, including spirometry, can be used to diagnose and manage respiratory problems.
Some possible causes of a relatively low FEV1/FVC ratio include:
- Chronic obstructive pulmonary disease (COPD)
- Asthma
- Chronic bronchitis
- Emphysema
- Other respiratory conditions.