What does a low forced expiratory volume (FEV1) indicate?

A low forced expiratory volume in one second (FEV1) is indicative of possible obstructive lung disease. FEV1 measures how much air a person can forcefully exhale in the first second of a breath. In obstructive lung diseases, such as asthma, chronic obstructive pulmonary disease (COPD), and emphysema, the airflow is limited due to obstruction or narrowing of the airways, which significantly reduces the FEV1.

In contrast, a normal FEV1 suggests that airflow is not significantly restricted, ruling out obstructive conditions. When FEV1 is low relative to the total forced vital capacity (FVC), it highlights that there is difficulty in expelling air quickly, a hallmark of obstructive pathology.

Other pathologies, such as restrictive lung disease, would typically show a reduced FEV1 but in conjunction with a reduced FVC, leading to a normal or increased FEV1/FVC ratio. High lung capacity does not directly correlate with low FEV1, as it does not indicate the efficiency or effectiveness of airflow. Thus, recognizing low FEV1 as a potential indicator of obstructive disease is crucial for respiratory assessment and management.