Definition/Introduction

Forced expiratory volume (FEV) is a critical measurement in pulmonary function testing that quantifies the volume of air a person can forcibly exhale from the lungs within a specific time frame following maximal inhalation. FEV is denoted with a subscript indicating the measurement duration in seconds (eg, 1 and 6 seconds), with FEV₁ and FEV₆ being the most common parameters.[1][2] Please see StatPearls' companion resource, "Pulmonary Function Tests," for more information. This test is essential for diagnosing and monitoring respiratory conditions such as asthma, chronic obstructive pulmonary disease (COPD), and other obstructive and restrictive lung diseases (see Image. Forced Expiratory Volume).

The most commonly used parameter, FEV₁, is the primary spirometric variable for assessing the severity of airflow obstruction and evaluating a patient's response to treatment. By reporting FEV₁ as a Z-score instead of a percent predicted, healthcare professionals can eliminate biases related to age, sex, and height, enabling a more accurate assessment of lung function impairment and the development of tailored management strategies.

The American Thoracic Society's current guidelines recommend replacing race- and ethnicity-specific equations with "race-neutral" averaged reference equations, such as the Global Lung Function Initiative (GLI) reference equations, while recognizing the need for further research to assess the impact of these changes.[3] FEV₆ can be a useful alternative to forced vital capacity (FVC).[2][4][5][6] Understanding and applying FEV measurements are essential for providing effective respiratory care and improving patient outcomes.

Issues of Concern

Spirometry is a test used to measure the ability of a person to inhale and exhale air over a specific period of time. Key parameters include FEV₁ and either FVC or FEV₆. Factors such as reduced patient effort, inadequate inhalation, difficulty following instructions, and certain medical conditions can impact the accuracy of spirometry results.[7] Technicians conducting the test must coach and motivate the patient to exert maximum effort to ensure accurate results. In the past, clinicians reported FEV as a percentage of predicted values based on age, gender, height, weight, and ethnicity.[8][9] A value of 80% of the predicted was traditionally considered the lower limit of normal (LLN).[10] 

The American Thoracic Society and European Respiratory Society now recommend using the fifth percentile, corresponding to a Z-score of −1.645 or lower, as the LLN to eliminate biases related to age, height, and weight bias and to account for the natural age-related decline in the FEV₁ to FVC ratio (FEV₁/FVC).[11][12][13] The Z-score is a combination of the percent predicted value and the between-subject variability, which provides a single number that accounts for age- and height-related lung function variability related to healthy individuals.

Growing evidence indicates that race- and ethnicity-specific equations underestimate the severity of pulmonary disease in Black populations. Current guidelines from the American Thoracic Society and European Respiratory Society recommend using race-neutral equations, such as the GLI reference equations. Although the GLI reference equations include data from individuals of various self-reported racial and ethnic backgrounds, race selection is not necessary for applying the formula.

Ongoing research is essential to assess the impact of adopting a race-neutral approach. A recent study indicates that race-based and race-neutral equations yield similar predictions for symptoms, healthcare utilization, and mortality. However, the prevalence of nonobstructive ventilatory impairments decreases among self-identified White and Hispanic individuals, from approximately 4.5% to 1.5%, while it increases among self-identified Black individuals, from 5.7% to 14%.[14] This reclassification could significantly affect standards for disqualification from certain jobs, such as firefighting, as well as eligibility for disability, prioritization for lung transplants, and disability compensation for veterans.

The FEV₁/FVC represents the fraction of air a patient exhales in the first second. This value is the most critical parameter for detecting airflow obstruction. Traditionally, an FEV₁/FVC of 0.7 has been considered normal. However, this fixed ratio can result in overdiagnosis of airflow obstruction in patients aged 70 or older and underdiagnosis in younger individuals. Reporting FEV₁/FVC as a Z-score, with a threshold of −1.645 or lower as the LLN, helps reduce the incidence of misdiagnosis.

Spirometry requires substantial effort and can increase pressure in the chest, abdomen, head, and eyes. Patients who have experienced a myocardial infarction within the prior month or who have unstable angina should avoid spirometry. Additionally, patients who have undergone abdominal, intracranial, or eye surgery, or those with a pneumothorax in the prior 6 weeks, should not undergo spirometry testing.

Clinical Significance

Patients may undergo spirometry for various reasons, including chronic persistent cough, wheezing, dyspnea, and exertional cough or chest pain. Pulmonary function tests objectively measure a patient's response to bronchodilators, monitor disease progression, assess levels of respiratory impairment, and evaluate the effects of exposure to chemicals in the workplace. Technicians record the highest FVC, FEV₁, and FEV₆ from 3 attempts as the final result. A low FVC may result from poor patient effort, airflow limitations, or restrictions caused by diseases affecting the lung parenchyma, pleura, or thoracic cage. FEV₁ measures the mechanical properties of the lungs; FEV₁/FVC helps differentiate between obstructive and restrictive lung diseases. FEV₁ accounts for approximately 75% to 85% of the FVC in healthy lungs.

Both restrictive and obstructive disorders cause a reduction in FEV₁. In obstructive diseases, FEV₁ is disproportionately reduced compared to FVC, resulting in FEV₁/FVC falling below the LLN. While FEV₁ is the most important measurement for assessing the severity of airflow obstruction, FEV₁/FVC is essential for detecting airflow obstruction. However, this ratio is still not a reliable indicator of disease severity. Clinicians use FEV₁ to monitor disease severity in patients with COPD and asthma.

FEV₁, FVC, and total lung capacity are reduced in restrictive disorders, leading to a normal or elevated FEV₁/FVC. Please see StatPearls' companion resources, "Emphysema" and "Chronic Emphysema," for more information.[15] Some authors suggest that FEV₁/FEV₆ may serve as a replacement for FEV₁/FVC, as FEV₆ offers improved accuracy, requires less physical effort, and is more reproducible.[16]

The most common causes of decreased FEV₁ include airway obstruction from bronchospasm, airway inflammation, loss of lung elastic recoil, and increased airway secretions. The change in FEV₁ after the administration of inhaled bronchodilators can help assess the reversibility of airway obstruction. An increase in FEV₁ of 10% or more following bronchodilator use is considered a positive response.[17] A positive response is typically observed in reversible airway obstruction, such as asthma. However, clinicians should be aware that a lack of significant improvement in FEV₁ alone does not necessarily indicate that the patient will not benefit clinically from bronchodilator therapy.[18] 

Additional indicators of beneficial bronchodilator effects include significant increases in inspiratory capacity (IC) or vital capacity (VC) after treatment. In contrast, nonreversible obstruction, as seen in patients with COPD, will not show a significant positive response to bronchodilator administration. Please see StatPearls' companion resource, "Emphysema," for more information.[15][19] 

Nursing, Allied Health, and Interprofessional Team Interventions

FEV is a crucial measurement in pulmonary function testing that quantifies the volume of air a person can forcibly exhale within a specific timeframe following maximal inhalation. This measurement is crucial for diagnosing and monitoring respiratory conditions such as asthma, COPD, and other obstructive or restrictive lung diseases.

FEV₁, combined with FVC, is the most commonly used parameter for identifying airway obstruction. FEV₁ is also a reliable indicator of disease severity and is used to monitor patients with COPD and asthma. However, comparing FEV₁ to predicted values based on age, gender, height, and ethnicity is no longer recommended.

All spirometry values currently use the fifth percentile as the LLN, corresponding to a Z-score of −1.645 or lower, to eliminate age, sex, and height bias and support tailored management strategies.[20] in addition, race-neutral formulas are recommended for calculating predicted spirometry values to reduce racial bias in healthcare. 

Accurate spirometry depends on good patient effort, proper inhalation, and the ability to follow instructions, as decreased effort can result in misdiagnosis and inappropriate treatment. In obstructive diseases, FEV₁ is disproportionately reduced compared to FVC, leading to a low FEV₁/FVC with a Z-score of −1.645 or lower. In restrictive disorders, both FEV₁ and FVC are reduced, causing FEV₁/FVC to remain normal or elevated. Some experts suggest using the FEV₁/FEV₆ instead of FEV₁/FVC, as FEV₆ offers greater accuracy, lower physical demands, and improved reproducibility.

The FEV₁ response to inhaled bronchodilators can help assess the reversibility of airway obstruction. However, clinicians should be aware that a lack of significant improvement in FEV₁ does not necessarily indicate that the patient will not benefit from bronchodilator therapy. Clinicians should consider changes in other values, such as IC and VC. Understanding and utilizing FEV measurements are fundamental in delivering effective respiratory care and improving patient outcomes.

Enhancing patient-centered care, outcomes, safety, and team performance related to FEV measurement requires a multidisciplinary approach involving physicians, advanced practitioners, nurses, pharmacists, and other healthcare professionals. Physicians and advanced practitioners must be proficient in conducting and interpreting spirometry tests, especially FEV₁ and FVC, to effectively diagnose and monitor respiratory conditions such as asthma and COPD.

Healthcare team members must collaborate to prepare patients for spirometry, ensure accurate technique, and educate them on the importance of these tests and proper inhaler use. Adhering to standardized spirometry protocols and participating in quality improvement initiatives are essential for enhancing accuracy and effectiveness.

Effective interprofessional communication is crucial and can be improved through meticulous documentation and timely sharing of specialist input and test results. Collaborative care planning and patient education are essential strategies, enabling all healthcare team members to work together in creating and adjusting treatment plans based on spirometry results and patient responses. By integrating these skills, strategies, and communication practices, healthcare teams can significantly enhance patient-centered care, safety, and outcomes in managing respiratory conditions through FEV measurements.