What is Forced Vital Capacity (FVC) in a patient with a history of respiratory disease, such as Chronic Obstructive Pulmonary Disease (COPD) or asthma?

What is Forced Vital Capacity (FVC)

FVC is the maximum volume of air that can be forcefully exhaled after a maximal inspiration, measured during spirometry, and serves as a critical parameter for diagnosing and assessing airflow obstruction when combined with FEV1 in the FEV1/FVC ratio. 1

Definition and Measurement

FVC represents the total amount of air expelled during a forced expiratory maneuver after taking the deepest possible breath. 1 This measurement is obtained through spirometry and is fundamental to evaluating lung function in patients with respiratory diseases, particularly COPD and asthma.

Clinical Significance in COPD

Diagnostic Role

• The FEV1/FVC ratio is the primary diagnostic criterion for COPD, with both GOLD and ATS/ERS guidelines defining airflow obstruction by relating FEV1 to FVC. 1
• Post-bronchodilator FEV1/FVC <0.7 confirms COPD diagnosis, ensuring that only persistent airflow obstruction is identified. 1
• The FEV1/FVC ratio is a relatively sensitive index of mild COPD, while in moderate to severe disease, FEV1 severity is best assessed in relation to reference values. 1

Important Measurement Considerations

FVC may underestimate true vital capacity in COPD patients with increased small airway collapsibility, potentially causing the FEV1/FVC ratio to underestimate or fail to detect airflow obstruction. 1 This occurs because:

• Gas trapping increases residual volume (RV), which decreases inspiratory capacity (IC) and FVC. 1
• In patients with significant gas trapping, pre-bronchodilator FEV1/FVC may appear ≥0.7 (falsely normal). 1
• Bronchodilators can reduce gas trapping and increase FVC (volume response), sometimes more than FEV1, thereby decreasing the FEV1/FVC ratio to <0.7 and revealing true obstruction. 1

Volume vs. Flow Responses

Volume Responders

• Volume responders are characterized by lower baseline FEV1 and FVC with higher RV, showing greater improvements in FVC relative to FEV1 after bronchodilator administration. 1
• These patients demonstrate greater dynamic airway collapse and gas trapping. 1
• Volume responses may occur in the absence of flow responses, particularly in more severe COPD. 1

Clinical Implications

• Flow responses decrease in more severe COPD patients, while volume responses become more prominent. 1
• In the ECLIPSE study, GOLD grade 2 patients showed post-bronchodilator increases in FEV1/FVC ratio (due to greater flow responses), while grade 4 patients showed decreases (due to greater volume responses). 1

GOLD 2025 Recommendations

GOLD 2025 recommends using pre-bronchodilator spirometry to rule out COPD and post-bronchodilator measurements to confirm the diagnosis. 1 This approach:

• Reduces clinical workload by avoiding unnecessary post-bronchodilator testing in clearly normal cases. 1
• Ensures volume responders are not overlooked. 1
• Limits COPD overdiagnosis by confirming persistent obstruction. 1
• Post-bronchodilator results close to the threshold should be repeated to ensure correct diagnosis. 1

FVC vs. Slow Vital Capacity (SVC)

The 2005 ATS/ERS Task Force recommended using the largest available vital capacity (whether IVC, SVC, or FVC) rather than FVC alone. 1 However:

• GOLD 2025 maintains that airflow obstruction should be identified using the FEV1/FVC ratio. 1
• If there is strong clinical suspicion of COPD with normal FEV1/FVC ratio, further investigations including FEV1/SVC ratio assessment should be considered. 1
• This is particularly relevant for symptomatic patients <60 years old and obese individuals, where FEV1/SVC may detect mild peripheral airflow obstruction missed by FEV1/FVC. 1

Severity Classification

With moderate COPD (FEV1 56% predicted and FEV1/FVC 64%), the reduced FEV1/FVC ratio confirms obstruction while FEV1 percentage predicted determines severity. 2 The European Respiratory Society defines moderate COPD as FEV1 50-69% predicted in the presence of obstruction. 2