What does a forced expiratory volume (FEV1) less than 80% of predicted values typically indicate?

A forced expiratory volume (FEV1) that is less than 80% of predicted values is typically indicative of possible obstructive lung disease. FEV1 measures the volume of air that can be forcibly exhaled in the first second of expiration, and a reduction in this value suggests that there is a limitation in airflow, which is characteristic of obstructive conditions such as chronic obstructive pulmonary disease (COPD) and asthma.

In obstructive lung diseases, the airways are narrow or blocked, making it more difficult for air to flow out of the lungs quickly. When FEV1 is less than 80% of the predicted value, it reflects this reduced airflow and thus raises suspicion for obstructive pathology.

On the other hand, restrictive lung disease would typically lead to a reduced total lung capacity and could affect FEV1, but the FEV1/FVC ratio (forced vital capacity) would often remain normal or can be increased. Normal lung function would indicate that FEV1 is within the predicted range, and a severe asthma attack would likely present with even more pronounced reductions in FEV1, but the key takeaway for this question is that the value of less than 80% specifically points towards potential obstructive lung disease